Custom:(adjective) "Made or done to order for a particular
customer" We make these parts to order since every pair of
shims if likely a unique combination of length, width, angle, and
If you've found this web page it's likely because some change has been
made to your vehicle's suspension and now you're experiencing some
issues with drive shaft vibration and/or steering. As such, realize you
no longer have a stock vehicle, as a stock vehicle is usually set up
properly from the factory. We don't know what has been done to modify
your vehicle. As such, we don't go by "X model, Y year"
vehicle, instead our parts are made to the dimensions you provide us as
to the angle, length, width, etc. shims or blocks that you feel would
fit on your vehicle. Also, realize that this isn't a simple matter of
looking up a number in a table. For example, we once ran into an
on-line shop that listed a 3" lift needed a 3° shim and a
6" lift neded a 6° shim. That seemed simple enough, the
3° shim was installed with a 3" lift and vibrations ensued.
It turns out, removing that shim was the fix, so no shims were needed
for that lift. And you'll also run across "experts" who'll
tell you to "point the pinion at the transfer case" or
similar "rule"without so much as looking at your vehicle. If
it were that easy, this web site wouldn't exist, nor would it be so
long and detailed. Our goal is for you to understand what the cause of
your particular problem is and then understand how to go about fixing
On leaf-sprung vehicles, shims (or wedges) are often used to modify the
angle between the spring perch on the axle and the leaf spring itself.
The correction may be needed because of longer spring shackles tilting
the pinion out of alignment, or to change from a single-cardan to a
double-cardan drive shaft (for increased drive line angle capability),
or to correct steering geometry (so your trucks handles better). An
alternative to shims is to cut off the spring perches and re-weld new
ones on at the corrected angle, but this is a lot of work and requires
careful measurement to get things lined up properly.
Anyway, for whatever reason you need a shim, you do need one. And if
you need one you probably need an exact angled one, not just the angle
or two the shop has. When I needed shims, I found one shop that had
3° and 6°, and another that had 4° and 8°. All of
these shims were aluminum, and not the nice strong billet aluminum, no
they were cheap cast aluminum. Cast aluminum can be brittle, and it
tends to fatigue or deform over time, and ultimately break. On the rear
axle, this can be a pain if it happens on the trail, if it happens on
the front axle, this can be downright dangerous.
Since I had only been able to find low quality cast alloy shims
available and only in limited angles, I decided to make my own shims
from a solid piece of mild steel, cut to the desired angle. Then a flat
seat for the center bolt head is cut into the base to eliminate stress
at that critical point. These shims are much more resistant to breakage
than cast alloy shims. After locating a material source, developing the
mfg. process, and forming a company to produce them, 4Crawler Offroad
can now make these made-to-order shims available to others. If you want
to "roll your own", click here
for a VRML model of my shim design (5°). These shims are used
to correct drive line and steering angles on leaf-sprung vehicles. Feel
free to read my article on measuring
drive line angles here before ordering. Finally, for permanent
mounting, steel shims can easily be welded to the spring perch. No
worries about shims breaking, twisting or falling out on the trail.
Lift blocks are similar to shims, except they are designed to add lift
(to a spring over axle) or drop (to a spring under axle) and optionally
may have a bevel cut in the top for pinion angle correction. Common
aftermarket blocks use extruded aluminum sections. The thin wall
material is prone to fatigue and cracking. 4Crawler Offroad can also
make solid billet aluminum lift blocks with built-in angles. With the
solid material, the blocks will hold up to the heaviest vehicles and
Below, you can see a few versions that 4Crawler Offroad has produced
over the years:
Photo A: Is a bolt-on shim, it is drilled for the center bolt to go
through, there is a bolt head relief flat ground or milled to allow the
bolt head of the center bolt to rest flat, then the shim is bolted to
the rest of the spring pack. With aluminum shims, this is your only
option. This shim has also been precision machined in the "high accuracy shim" option.
Photo B: In the center is a picture of an 8° weld-on shim. Since
the shim is steel and the spring perch is steel, one way to ensure the
shim stays put is to weld it to the spring perch. Then, the head of the
center bolt goes into the hole in the shim, so you don't need to remove
or replace your old center bolt.
Photo C: On the lower right is a custom width 2° bolt-on shim,
3" (76,,) wide, 5-3/8" (136mm) long cut from 3/8" (10mm)
stock for minimum thickness
Below is a closeup of some of the design details 4Crawler Offroad
incorporates in the shims. First is the above mentioned center bolt
head relief pocket. By creating a flat pocket for the head of the
center bolt (on bolt-on shims) you prevent stress on the center bolt
which could otherwise cause the head of the bolt to bend, as pictured in this photo. Also, each
shim is stamped in 1 or 2 places with the angle it was cut to. This
will come in handy down the road when you need to change angles for
whatever reason. On several occasions, customers have run into trucks
with existing shims (of unknown angle) where it is needed to add or
subtract a few degrees. Without pulling the shim out, its very
difficult to get an accurate angle off it. With the angle stamped into
the end and the face, it should be visible in most situations.
Closeup of shim details
Weld-on vs. Bolt-on shim
In the image above-right, is pictured a weld-on and bolt-on shim with a
spring center bolt in the middle. The weld-on shim has a center bolt
hole large enough for the head of the center bolt to fit. The shim
itself is designed to be welded to the spring perch, in effect becoming
a permanent part of the perch. The bolt-on shim has a center bolt hole
only large enough for the shaft of the center bolt to fix. The head of
the center bolt then fits into the machined pocket in the shim and then
engages the hole in the spring perch as normal. In this case, the shim
becomes part of the spring pack.
Note the difference between the thin shims and the thick tapered
blocks. In the shims, there is only a hole in the middle. In the
blocks, there is a hole on one side and a pin on the other side. So,
can shims be made with a hole/pin combination? Unless the center of the
shim is thicker than 3/4" (19 mm) - 1" (25 mm), there is
simply not enough room for a hole deep enough for the head of the
center bolt (they can be up to 1/2" (12,5 mm) tall) and the
pressed in pin, which needs to be 3/8" (10 mm) or so deep. Since
all the "shims" are made under 1/2" (12.5 mm) thick,
they can only be had in the through-hole design. If the hole/pin design
is desired, then a tapered block will be required.
Order both the shim and the desired thickness spacer and the shim will
be supplied welded to the spacer.
These shims will be made from laminated/welded steel to increase the
thickness/length as needed. As such, the finish will not be as clean as
the shim cut from a single piece of steel. If this is an issue for you,
you might consider ordering shims from another supplier.
If this is an issue for you, you might consider ordering shims from
Or order 2 shims and the material will be laminated/welded to increase
the thickness for a single shim.
The shim design minimizes the length of the center bolt, but if your's
is near the end of its length, you may need to use a longer center
bolt. It needs to be long enough to pass through all the leaves of your
spring pack, the shim and any blocks you may have as well leaving
sufficient threads exposed for the retaining nut. The shim thickness
will vary with the angle, a 3° shim adds about 3/16" to the
bolt length, 5° about 1/4", 8° about 3/8", etc.
Note, this shim option applies to only a single specification exceeding
the above limits, if you need a high angle and an extra wide shim, or
your shim is more than 1" longer than the length/angle
limits, order the shim option below.
Cost: US$55.00/pair (i.e. 2 shims) plus shipping and applicable sales
And now available, low offset relocation places for those needing to
relocate the axle less than 3/4". These plates will be 3/4"
thick and allow center hole/pin offsets of 0" - 3/4". This is
due to needing to have plate depth to drill a 5/8" center bolt
hole 3/8" deep in one side of the plate (to accommodate the head
of the existing center pin) and to seat the 5/8" center pin
~3/8" deep in the other side of the plate. Specify the offset of
the single offset hole in the "Note to Seller" field of the
Lengthens the e-brake arms to clear taller spring packs, or when
running blocks and/or thick shims
Can be drilled to raise the e-brake lever attachment point between
1" and 2"
With the spring over axle configuration, it is possible that adding a
thick shim or spacer between the axle and springs can lift the top of
the spring pack high enough that the e-brake cable rubs on the springs.
This can reduce e-brake effectiveness and can cause damage to the cable.
The extensions include a hardware to attach them to the e-brake arm and
are shipped without a top hole drilled.
This allows you to raise the e-brake cable just enough for your needs.
NEW: Also available with pre-drilled top holes for ease of installation.
Also suitable for use in a horizontal orientation to lengthen the
e-brake cables for use on a wider rear axle
For example when upgrading from an '85 or earlier to an '86 or later
rear axle that is 3" wider, the existing e-brake cables will be
1.5" short on each side.
P/n: E-BrakeExts, Cost: US$15.00/pair (i.e. 2 extensions) for the blank extensions or
US$20.00 for extensions with pre-drilled holes 1", 1.5" or 2"
offset from the bottom hole plus shipping and applicable sales tax:
Unless otherwise specified, center bolt holes will be drilled
for 3/8" hardware (bolt -on shims) and 5/8" bolt head (for
weld on shims) and the hole will be centered in the shim.
For center bolt holes larger than 5/8" (up to 1" maximum
dia.), add US$5.00 for the extra machining time involved.
Note 5/16", 10mm and 7/16" center bolts are also used,
likewise, head sizes can range from 1/2" up to 3/4"
Jeeps often use 5/16
Toyota commonly uses 3/8" or 10mm
Ford uses 1/2"
If you are unsure of what size hole to specify, you can order shims w/o
center holes or 5/16" and drill to match your vehicle.
This applies to blocks with pressed in centering pins, the default pin
size is just under 5/8", and the opposite hole is 5/8"
diameter by default
You can also specify off-center (e.g. 3/8" hole offset 1"
toward the thick or thin edge of the shim) or multiple holes.
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For oversize shim orders shipped outside the US, additional shipping
charges may apply:
Regular international shipping covers shipments up to 4 lbs., this is
sufficient to cover most shim/block orders
However, for extra thick/large shims, weighing over 4 lbs., additional
shipping charges may apply:
You will be notified once the items are ready to ship if this applies
to your order.
For an estimate on whether this applies to your order, a shim/block
volume larger than 12 cu.in. will tend to exceed the 4 lb. limit;
e.g. a 2.5" wide, 5" long, 8 degree shim would probably
exceed 4 lbs. and incur additional shipping charge.
Note: For shims wider than 2", most shims of 5 degrees and higher
will be cut from 1" thick stock, so volume will be width * length
* 1" cu. in.
For shipments to California, add applicable state sales tax
(automatically added by PayPal).
The best answer is that you would have measured all your drive line
angles before and after modifying the suspension. That way you would
have some baseline measurements to use to restore smooth operation
after the modifications. Unfortunately, nobody seems to remember to
measure before slapping on the new suspension, so you'll need to resort
to one or more of the techniques below...
- You might contact the lift supplier and ask them what angle shim they
recommend for your type of vehicle with their lift installed.
Spring manufacturers should be able to supply this information to you.
You may find someone else (on a web forum, Facebook group or mailing
list) who has done a similar modification to their vehicle (that is
similar to yours) and find out what angle shim they used for their
Luckily, the Internet offers a great resource in finding this sort of
information. For example if you have an early Ford Bronco,
here is a great link. That link was found with a simple web
Short of finding out from someone else what angle shim is needed, the
only real way to know is to measure the angles. Since you are even
considering adding shims means you have somehow modified your vehicle.
Either you have added lift, changed springs, installed longer shackles,
moved spring hangers, etc. You need to get some simple measurements to
determine if shims are needed and if so, what angle shim is required.
For rear axles, you only have the worry about the angle of the pinion
in relation to the driveshaft.
Not able to measure the angle shim you need? No problem. If you can set
up your axle at the proper angle and measure the height difference
front-rear on the spring perch as well as the length of the spring
perch, we can work out that angle from those measurements. For example,
if there is a 1.5" difference over a 6" long perch, that
works out to a 14° angle.
Axle Wrap considerations:
Allow for 1° - 2° rotation at the pinion end of the shaft to
account for this. Rear axle will tilt up and front axle will tilt down
under load. This can be influenced by the stiffness of the springs, the
weight and aero drag of the vehicle, height of any suspension lift
blocks (taller = more wrap) and the size of the tires and even axle
gearing. Anything that puts more torque through the axle and causes it
to "wrap" or twist under the springs will increase the angle
change under load. It's all fine to have your pinion angle dialed in to
a fraction of a degree in the driveway, but what matters is where it
sits when you're driving down the highway at speed.
Single-cardan or u-joint drive shaft considerations:
Ideally, you would point the two u-joints would be at equal and
opposite angles of each other. Real world, you have axle wrap. That is,
the leaf springs are going to deform under the torque of accelerating
or driving down the road at speed, see above. Another consideration is
that the vibration cancellation in u-joints diminishes the higher the
operating angle is. In our experience, once you get much over 10°
operating angle, your shaft may vibrate, depending in it's length,
tubing dimensions and RPM. It may be worth looking into getting a
double-cardan or CV style shaft made.
Front axle pinion and caster angle considerations:
For a leaf-sprung front axle, you can use the above measurements, but
they only consider the pinion/driveshaft angles. You want to first
address steering angles up front (unless you have a trail-only rig)
first then worry about pinion angles. After all, if you have to choose
between having proper steering geometry or a proper pinion angle (so
that you can use 4WD at speed), I would choose proper steering angle
any day? Why? Well if you can't drive the truck in a straight line on
the road, having 4WD available at high speed becomes a moot point. I
have had bad caster angle on my truck and I can tell you that the term "death
wobble" is aptly named! When that front end starts
hopping all over the road and seems to get progressively worse as you
drive is not fun. Give me good solid steering anyway and I can live
with a little front driveshaft vibration if I need to use 4WD at higher
speeds every once in a while.
So how do you measure the steering caster angle? Best is to go to
an alignment shop and have them put your truck on the alignment machine
and give you a printout of the angles. You'll get a list of toe-in,
camber and caster as-measured and they may tell you what the angles
should be. If not, consult your owners manual or a good repair manual
for your vehicle. As far as what angle to use, its a direct
relationship between the number of degrees your caster angle is off and
the angle of the shim. For example if your vehicle specs +2° of
caster and you are at +5° or -1°, you'll need a 3° shim
(that is 5° - 3° = 2° or -1° + 3° = 2°),
and just install it in the proper orientation to correct the angle.
If running taller than stock tires, you may want to reduce the caster angle
a bit. The reason being that the effect of caster angle is to give a horizontal
separation between center of the tire's contact patch and the point where the ball
joint or king pin axis would intersect the ground. The taller the tire, the
less angle is needed to create that same separation.
Here is a link to
Toyota solid front axle steering alignment specifications.
On the Toyota front axle, an angle of approx. 6° up (front of
perch higher than the back) on the spring perch provides a decent
caster angle (Note: this measurement is related to but not the actual
caster angle). At this caster angle, the stock front pinion angle will
be tipped up ~5° from horizontal (or 85° from vertical). So
every degree you tip the pinion up/down will result in the same caster
angle change. Too little caster will give poor return to center and wandering at speed.
Too much caster will give a heavier feel to the steering. Best to shoot for a caster angle in the
middle of the range. Realize that the caster angle will change as you change the rear ride height,
either due to changing the suspension or adding load.
This can be in the range of 2/3 - 1#176; per inch of ride height change.
It is not uncommon for the caster angle to be off different amounts on
each side of the axle. If so, this means that the front axle housing
itself is not quite aligned side to side or that it is slightly bent.
Best bet is to get a shim to correct the average of the two angle
errors. Short of cutting off one steering knuckle and turning it to
align with the opposite side, its unlikely that you'll be able to
"twist" the front axle housing by using two different angle
shims. If you think about it, you have a rigid steel housing attached
to two flexible leaf springs with some shims in between.
And if you want to correct BOTH the caster and pinion angles at the
same time, the only way to do that properly is to cut and rotate the
steering knuckles on the axle to set the proper caster angle and if
needed cut and relocate the spring perches (or add shims) to set the
proper pinion angle. Here is
a write-up on doing this modification on a Toyota solid front axle. On
some axles, like the Dana 44, you may find that one of the spring
perches is cast into the side of the differential housing and is
therefore difficult to modify. In that case, you can either use two
shims to change the pinion angle, or cut/relocate the separate perch
and then add a single shim to the cast perch to
set the pinion angle.
If you are unable to modify the front axle housing, another option is
to have a custom front drive shaft made. Replace the lower u-joint with
a CV joint and this will eliminate any issues with the pinion angle
being out of alignment with the shaft angle.
Realize that the front axle and pinion will tip down under load (when
driving forward), so it's the opposite of the rear shaft. If you have a
front CV shaft, you'll want the pinion angle to be 1° - 2°
above the angle of the driveshaft to allow for this down tilt. However,
if you have a front drive shaft that spins all the time, like with the
"shift on the fly" type 4WD systems (like Toyota's Automatic
Differential DIsconnect or ADD system), then you'll likely want the
front u-joint angle in-line with the shaft angle. Why? Because you'll
mainly be concerned with the shaft running smooth, while spinning
freely, rather than under load which you may only do off-road in 4WD.
Also, don't worry about a 0° u-joint angle "burning up"
the u-joint. Why? Because it's running at no load, so no chance of
"brinelling" which is where the needle bearings pound dents
in the races over time. And also, unless you are driving on a glass
smooth road for hundered of hours on end, any bumps int he road will
cycle the suspenion enough to move the u-joint. Rough rule of thumb is
an inch of ride height change is about 1° of u-jount angle change.
Finally, with regards to shimming the front axle. If you have a
steering setup with the tie rod and/or drag link above the springs, you
need to be sure there is enough clearance over the springs for the
steering linkage to pass when adding a shim. Since the shim will add
thickness and raise the spring pack off the axle/perch, you'll need to
ensure adequate clearance for the thickness of the shim.
CV or double cardan drive shafts:
Ideally, you would point the pinion directly at the CV joint, that is
the pinion u-joint wou,ld be at a 0° operating angle. Real world,
you have axle wrap. The leaf springs are going to deform under the
torque of accelerating or driving down the road at speed. Allow for
1° - 2° rotation at the pinion end of the shaft to account
for this. Rear axle will tilt up and front axle will tilt down under
Shaft angle changes with pinion angle change:
One complication arises when changing the pinion angle on a driveshaft.
As you change the pinion angle, the driveshaft angle is also changing.
Tipping the pinion up reduces the angle of the shaft. Tipping the
pinion down, increases the angle of the shaft.
It's relatively easy to determine the relationship of the relative
change in the two angles. The angles change by the ratio of the
respective lengths of the driveshaft and the pinion extension from the
axle center line. Lets say that you measure the distance from the
center of the axle to the pinion flange / u-joint yoke and find it is
12" (as measured on a Toyota 8" axle). And lets say the
driveshaft measures 60" long from the transfer-case output flange
to the pinion flange. This results in a 1 in 5 ratio, meaning that for
every 5° of pinion angle change, the driveshaft angle will change
1/5 of that or 1°. This is easy to see if you sketch out the
driveshaft and pinions to scale. Since the shim is tilting the axle at
it's center line and the pinion sticks out away from that center line,
it moves up and down as the angle changes. This means the bottom end of
the driveshaft moves up and down by the same amount. But since it is
much longer than the pinion length, the angle change is reduced by the
ratio of the two lengths.
Another way to look at it it that the pinion will tip up (or down) by
exactly the angle of shim you insert between the spring perch and
spring. That angle change will raise (or lower) the u-joint attached to
the pinion. Since the bottom end of the drive shaft is attached to that
same u-joint, it will rise (or fall) by the same amount. But since the
shaft is typically longer than the axle-pinion joint length, it will
move fewer degrees than the pinion was rotated. It will move at the
inverse ratio of the shaft to pinion length.
For a practical example, assume a 20° driveshaft angle and a
10° pinion angle, with a pinion length of 12" and a
driveshaft length of 60". Tthis gives a 1:5 ratio (12 / 60) of
angle changes. So, starting with the 10° difference, we want to
end up with the pinion angle 1° - 2° below the driveshaft
angle. Installing a 7° shim, we would find that the pinion angle
would increase from 10° to 17°. But at the same time, the
driveshaft angle would decrease by 7° x 1/5 or 1.4°, so it
would end up at 18.6° (20° - 1.4°). This leaves an angle
difference of 1.6°, which is within the 1° - 2° below
target we were shooting for.
For another example, assume a short wheelbase Jeep with 20°
driveshaft angle and a 5° pinion angle, with a pinion length of
12" and a driveshaft length of 18". This gives a 2:3 ratio
(12 / 18) of angle changes. So, starting with the 15° (20 - 5 =
15) difference, we want to end up with the pinion angle 1° -
2° below the driveshaft angle. Installing an 8° shim, we
would find that the pinion angle would increase from 5° to
13° (5 + 8 = 13). But at the same time, the driveshaft angle would
decrease by 8° x 2/3 or 5.3°, so it would end up at
14.7° (20° - 5.3°). This leaves an angle difference of
1.7°, which is within the 1° - 2° below target we were
Your measurements will likely be different than the above examples, use
your measurements to work out your ratios and then follow the same
steps. Also, don't get too hung up on the exact numbers and carrying
out the ratios to a high degree of accuracy. If your shaft measures
17.5" instead of 18" in the above example, using 18 instead
of 17.5 results in about a 2% ratio difference which would in turn work
out to about 1/4° angle difference. You are just trying to get
within a degree or two of the ideal alignment, +/- 1/4° is in the
noise. And realize, this happens for both u-joint/single-cardan and
CV/double-cardan shafts. Although on a u-joint shaft, both the upper
and lower u-joint operating angles will change by the same amount. On a
CV shaft, the same is true, but, while the CV joint could care less
about the angle, the bottom u-joint will no longer be near 0° and
may start to vibrate. This same issue will also affect 2-piece shafts,
see below for more information on that setup...
2-piece drive shafts (i.e. center support bearing):
For applications with 2-piece drive shafts (i.e ones with a Center
Support Bearing or CSB), there is often confusion about what to do
about the CSB. Some folks think it is necessary to shim the CSB to
correct the driveshaft angle. This is not something you want to do in
all cases. Why? We have an in-depth discussion of how to
set up 2-piece drive shafts here, but in short it comes
down to understanding how the 2-piece shaft was designed to operate by
the vehicle mfg.
One option is to set the upper u-joint and shaft to 0° and then
look at the bottom half of the shaft only, it is either a single-cardan
(u-joint) or double-cardan (CV joint) shaft and you just measure and
correct the angles on that part of the shaft. So just treat the bottom
half of the 2-piece shaft like any other driveshaft and forget the
upper half. In other words, treat the two halves of the driveshaft as
independent parts, separated by that CSB. So, if you made no changes
that affected the transmission/transfer case to CSB (which is attached
to the frame) part of the shaft, you should also not make any changes
to that part of the drive shaft. If instead, you made changes that
affected the CSB to axle portion of the shaft, then that is the part
you need to correct.
Another option on a 2-piece drive shaft that has 3 u-joints is to treat
the upper shaft section as sort of an extended CV joint. That is the
two u-joints on that section of shaft should be equal to each other and
they should also align (i.e. they are in phase). Then the bottom
u-joint, at the axle, is set to 0° operating angle relative to the
drive shaft (i.e. the pinion u-joint "points at" the carrier
bearing u-joint). But if you have a 2-piece drive shaft with 3
u-joints, one of those u-joints should be at 0° and the remaining
two should be at equal and opposite angles. So pick the u-joint that is
closest to 0° and then set the other two u-joints to equal and
opposite angles. It all depends on how the drive shaft was designed and
set up at the manufacturer and how you have modified the vehicle (if
applicable). But in any event, if you have 3 u-joints on the shaft,
eliminate one of them by running it at 0° and then just worry
about the remaining 2 u-joints.
Traction Bar considerations:
If running a traction bar, of some sort, that limits axle wrap, then
the only real consideration to make is that you would want to set the
lower u-joint angle to the ideal angle for your type of drive shaft.
That is you don't leave the pinion 1° - 2 ° below the ideal
angle. So for a single cardan shaft, you would have both u-joint angles
the same and for a double cardan shaft, you would have the lower
u-joint angle at 0°.
4Crawler Offroad does not have a master database of all possible
vehicle and axle combinations (we tried to do this but it became such a
mess trying to keep track of every possible combination, that the data
was not reliable). And by the very fact that you need to add a shim,
you have a modified vehicle, the axle may or may not be stock, the
perches may or may not be original, and the axle itself may be a hybrid
of several different axle components.
You'll want the shims to be about the same length as the spring perch
on your vehicle's axle, which is very easy to do. One way to measure
that is to get the distance between the u-bolts (length and width). If
the axle is separated from the springs, just measure the spring perch
directly. And no need to get the length measurement to the nearest
0.001", usually to the nearest 1/4" is fine (6 mm). On some
vehicles, spring perches can be difference lengths (especially on front
axles). If this is the case, you would want to use the longest perch
length measurement, and let the other shim hang over the ends of the
perch. Shims can be made different lengths if requested, at an
additional cost of $10.00, if desired.
So why does the length of the shim matter? It should match the length
of the spring perch. If it is too short, the spring may not make
contact with the shim along it's full length, since it may hit the end
of the perch sticking out past the end of the shim. If the shim is much
longer than the perch, the thin end of the shim will likely just bend
down around the end of the spring perch and be ineffective. Likewise,
for any given angle, the longer the shim, the thicker the material it
must be cut from is. Since most applications desire as thin a shim as
possible (especially in a spring-under-axle situation), specifying a
6" long shims, for example, where a 4" shim would be
sufficient may in fact double the thickness of the shim.
For example on the Toyota mini-truck axles, the rear spring perch is
approx. 4-3/4" long, so the shims would be cut 4-3/4" long
for the rear axle. Jeep Wranglers have 4-1/2" long perches and the
early Jeep CJ models might be closer to 4" - 4-1/8" long.
However, some folks replace the stock spring perch with a u-bolt
eliminator kit, such as the one All-Pro Offroad makes. That kit uses a
6" long spring perch, so that is how long the shims should be.. A
polpular trend on Jeeps with spring over axle conversions is to use
7" or 8" long spring perches. The front Toyota mini-truck
axle spring perches are approx. 5-1/4" long, so that would be the
proper length for the front mini-truck axle. Other vehicles probably
have varying length spring perches, so don't use the above numbers,
grab a tape measure and find out for yourself.
There is no "standard length" for a spring
shim or rather there are many standard lengths! 4Crawler Offroad has
shims have been made in lengths from 3-1/2" to well over 6"
long. So bottom line, how long is the spring perch (front-back) on your
vehicle's axle (rear or front) to the nearest 1/4" or so. See
below for the measurement in question (note this is a modified Toyota
rear axle spring perch, stock length is 4-3/4", this one has had
3/8" extensions welded to each end to make it longer). In this
case the shim length would be about 5-1/2" long:
You really have 2 options, one is to run the standard 2" wide
shim, the springs really won't "know" the difference. If you
look at the spring perch itself, it probably has rounded edges
resulting in a flat area that is only about 2" wide. However,
4Crawler Offroad can make shims to the match the width of the springs
and/or perch if desired. There is an additional cost for shims over
2" wide due to the additional material and labor required to
For example, my Toyota 4Runner has springs that are 2-3/8" wide. I
run 2" wide shims and they work just fine. A full width shim might
resist twisting a bit better since it would be trapped in between the
u-bolts, or I can even fit a 2-1/2" wide shim in between the
u-bolts as the perch itself is 2-1/2" wide.
On a vehicle like the Toyota Landcruiser that uses 2-3/4" springs
or a full size rig with 3" wide springs, a full width shim
probably makes sense. Jeep Wrangler springs are 2-1/2", early Jeep
CJ springs may be 1-3/4" wide. So what is the "correct"
width to use? That's why this is an option, you order what you want. To
put it another way, if its worth the additional cost (to you), get the
custom width shim, if not, get the standard width.
Also, some vehicles have spring perches much wider than the spring. For
example, some early 1990s model Toyota pickups use a rubber lined metal
clamp around the springs (the purpose of which is not known) and thus
have a perch that is perhaps 1" wider than the actual springs. To
add shims to this vehicle, you generally need to remove the clamp and
then use a regular width shim. It would not really make sense to use a
3-1/2" wide shim on a 2-3/8" wide spring. Same story with
some of the u-bolt eliminator kits, they have a perch that is much
wider than the spring to allow room for the clamping bolt nuts to ride
below the perch.
On a related note, why do the custom width shims cost more than the
standard width shims? There is more material (and waste) involved in
the production of the custom width shims and also more labor. The
standard width shims are cut from lengths of 2" wide flat bar to
the exact length needed. On the custom width shims, they are cut to
width out of 6" wide flat bar then cut to length. Any excess is
scrap. The extra time and labor to make a 6" x 1" cut in
steel is significant as well. Finally, with the standard width shims,
4Crawler Offroad often will make several copies of the shim if the
length and angle are common. With the custom widths, the extra variable
means its unlikely that exact combination will come up again, so each
pair of shims is made to order.
See pictures below for examples of measuring the width of the spring
perch and the width of the spring. In this case the spring perch
measures about 2-1/4" wide, the spring is about 2-3/8" wide,
so you could use a 2", 2-1/4" or 2-3/8" wide shim for
this application, your choice:
In short, for the shim to do it's job, it must sit between the leaf
spring pack and the axle/spring perch. However, the shim will not sit
there all by itself, so you either need to attach it to the spring pack
or to the spring perch. With the bolt-on shim, you use the center
pin/bolt in the middle of the spring pack to also hold the shim in
place. Essentially the shim becomes just like another leaf on the
spring pack. In a spring-over-axle setup, the shims go on the bottom of
the spring pack, in a spring-under-axle setup, the shims go on top of
the spring pack. With the weld-on shim, you weld the shim to the spring
perch on the axle, thus the shim becomes part of the axle. With
spring-over-axle, the shim is welded o the top of the spring perch,
with spring-under-axle, the shim is welded to the bottom of the spring
perch. WIth both bolt-on and weld-on shims, the shims still end up
located between the spring pack and the spring perch.
Both types of shims are made of mild steel. Below are some of the main
1. Bolt-on shim has a small center bolt hole (typically 3/8" or
10mm) for the shaft of the center bolt, the weld-on shim has a larger
hole (typically 5/8"or 17mm) for the head of the center bolt.
2. Bolt-on shim will have a pocket
machined into the angled side to eliminate the angle for the
center bolt head, allowing it to sit flat. This eliminates the stress
riser in the center bolt that would otherwise be caused by the head of
the center bolt being tightened against the angle of the shim. The
weld-on does not have this.
3. Bolt-on shim is typically shipped painted to prevent rust, the
weld-on shim is shipped unpainted to allow welding it to the spring
4. A bolt-on shim may require a longer center bolt to hold it to the
spring pack. If the extra length of your center bolt is less than the
thickness of the shim, this would be the case. Longer center bolts are
available above. To determine the length, measure the height or thickness
of the spring pack that the center bolt passes through.
Allow extra length for the nut and the new shim (usually arounf 1/2") and that'll
be the length of center pin you need. We ha e various lengths available, be sure the
untreaded length is less than the thickness of spring pack.
A weld-on shim of course will not require any changes
to the center bolt (or even removing it from the spring pack for
installation), since the head of the center bolt simply fits into the
hole in the shim to locate the axle and springs properly.
A bolt-on shim can always be converted to weld-on at a later time:
Simply drill out the center bolt hole to accommodate the head of the
center bolt and weld it to the perch.
Which type of shim would be best for your application? Well, that is
all up to you. Both types will work equally well. Some considerations:
1. If you do not have access to a welder, then the bolt-on shim is the
best style for you.
2. If are unsure of the exact angle shim you need or have plans to
change your suspension at some time in the future, a bolt-on shim is
easier to change out down the road.
3. If you are sure of the angle shim you need and plan no future
changes and want a more permanent installation, a weld-on shim, once
welded to the spring perch, essentially becomes part of the axle.
4Crawler Offroad can typically machine the shims to +/` 0.5°
tolerance. Shims are checked after machining with a digital angle gauge
to ensure they are within this tolerance. Both shims are typically cut
from one block of material so the angles are identical between the
pair. This is typically more important than the exact angle. On
thickness, 4Crawler Offroad tries to get the two shims within
1/16" of each other, and within 1/16" variation in thickness
across the face of the shim
4Crawler Offroad can also make shims for Toyota front axles where the
10mm offset in spring perch heights can be built into the shim, making
the driver's side shim 10mm thicker than the passenger side shim. We
can do other thickness differences as well, within the material
If concerned about the slight difference in thickness, measure the ride
height of both sides of the vehicle and place the slightly thicker shim
on the low side for a spring-over-axle or on the high side for a
While this tolerance is typically fine for 99% of the customers, some
folks need higher accuracy. If your application depends a high accuracy
shim, you can order the item below along with your shims to get shims custom machined to
be typically within 0.010"-0.020" in thickness of each other,
and the angle within +/- 0.2 degrees (whole angles only and
shims of 6" length or less - see note below).
If you are the type of person looking for shims with a mirror finish
and tolerances of +/-0.001", you might want to look elsewhere for
shims, as you'll likely not be satisfied with these. We make these
shims to fit a practical application and once installed, they are
nearly invisible, so surface finish is not a design factor. And since
there is generally a bit of leeway in angle/length/width of the actual
shim installed. raising the machining cost by performing extreme high
precision operations does not really make sense. We try to offer a
custom made and serviceable part for a reasonable price.
Cost is $15.00 to cover the additional machining and setup time (note
this option is only applies to one set of shims (per option) and you
must specify it at the same time the shim order is placed):
If you already have a set of shims and want them machined to a tighter
tolerance, you may return the shims (US orders only) for re-work as
noted below (cost $15.00/shim + return shipping), or you may have a
pair of shims machined down to a thinner angle (for example from
4° to 3°): This option applies to angle changes of a few
degrees. For angle changes of more than a few degrees, the better
option is to order a new pair of shims as there may not be enough metal
in the shims for the new angle:
Shim re-work, US shipping
Shim re-work, International shipping
Note: The high accuracy option does not apply to any of
the high angle or extra long shims with the laminated construction.
This is because the laminated joints don't machine well with the milling
cutter. We can do this operation on the billet aluminum shims and
blocks because they are constructed of a single piece of material.
It all depends on which way you want the axle to rotate and how your
axle sits on the springs. Its easiest to think of the springs as being
rigid and fixed. Then visualize the axle being separate from the
springs and one solid part, that pivots about the springs. Then,
depending on which way you need to rotate the pinion to correct the
drive line angle, think of grabbing the axle and turning it (and the
pinion) to the correct the pinion angle. You should now be able to
"see" a gap between the spring perch and axle on one end or
the other, that's the side that the thick end of the shim goes in (i.e.
the shim fills this "gap). One other trick I've found to help
visualize this is to exaggerate the angles involved. Its hard to
"see" 3° but if you imagine 30° its a lot easier.
Placing the thick end of the shim on the pinion side of the axle will
tip the pinion up. Likewise, thick end away from the pinion will tip
the pinion angle down.
This reverses. If the thick end of the shim is on the pinion side of
the axle, the pinion will tip down. If the thick end of the shim is
away from the pinion, the pinion angle will tip up.
These shims are custom made to order to *your* specifications. As such,
they are generally not "in stock", since there would need to
be thousands of different combinations of angle, length, width, bolt
hole size and mounting style shims stocked to meet each and every
Shims can usually be custom machined and shipped in 1-2 weeks depending on backlog,
see backlog note below. Normal shipping is via Priority
Mail shipping from zip code 94088 which has 2-3 day delivery time in
most of the US and Priority Mail International (to many countries,
check the USPS.COM web site for
service info.) which takes 6-10 days internationally. In the US, shims
and blocks up to 1" thick are shipped in a Priority Mail envelope
and insured via USPS insurance. In the event of loss or damage to the
items, 4Crawler Offroad is happy to file an insurance claim on your
behalf for the item. When the claim is paid by USPS, the shims or
blocks will be re-made and replacements sent out. If you wish to have
replacement parts sooner, you can order a replacement set and when the
insurance claim is paid, those funds will be refunded to you for the
original purchase. If you wish to have the items sent with signature
guarantee in place of insurance, please indicate in the special instructions
on the order form. If you wish more accurate tracking of the items,
use the expedited Express Mail option below. If you wish to use a
different carrier or shipping method, inquire below.
Express handling and delivery (in the US, 1-2 day typical shipping
time) is also available starting at US$25.00 additional for the shims
and other parts, except for the larger custom tapered blocks. Please
inquire on exact shipping costs for the larger items like that.
Also, note that the standard shipping method (Priority Mail) only
offers a delivery confirmation number, while Express Mail offers full
package tracking information. So if you want detailed tracking
information, select this shipping option.
Order this item to upgrade the shipping on an previously
ordered set of shims or center bolts.
NOTE: Due to high order volume and supply chain issues, it may take some time for deliveries, production and shipments to catch up. Order backlog could be up to 12 weeks.
No problem, you can return the shims for credit against a new set. For
custom and standard width shims (excluding the high angle and extra
long variety) the credit against a new set of shims is $10.00. For the
new set, pay the cost of the new shims, less the $10.00 credit and add
return shipping and send back
the old shims to 4Crawler Offroad. For shims/blocks with
non-centered holes, or weld-on shims that have been welded on or other
modifications such as high angle or extra long, contact 4Crawler
Offroad for return/credit information. Generally for those types of
shims, can only offer to re-machine the shims if
For the custom aluminum tapered and lift blocks and the fabricated
steel blocks and shims, they are generally not refundable. We cut these
blocks from a large block of billet aluminum or weld up separate pieces
of steel to fabricate these parts to your specifications. Since these
parts are so specialized, the chances of us being able to resell them
in a timely manner is almost non-existent. We have an ever growing
stack of shims that we have accumulated over the years in doing single
shim orders or for exchanges and it is a very rare occasion where we
can pull something out of that stack to fill a new order. And since we
do at least 100 pair of shims to each pair of lift/tapered blocks, the
odds of getting a match are at least 100 times less. We'll be more than
happy to modify a block that you have ordered to a shorter lift height
or different angle, etc., but if you tell us you want X, Y, and Z and
we make you X, Y, and Z, then we have done our job. If you decide you
no longer want the part, you might see if you can put it up on eBay or
Craigslist or some venue like that. If you can find someone else who is
looking for that very part, they are likely to offer you more for it
than we can.
For 2 (or more) pair of shims made to the same specification, there is
a US$5.00 discount on the 2nd (and subsequent) pairs of shims, since
there is a savings on setup time for the machining. This discount will
be refunded upon shipment for on-line orders upon request, simply set
the order quantity to 2 (or more) pair of the desired shims, specify
the length, width and angle for the combined order. On multiple pairs
of shims (of differing specifications) shipped to the same address,
there is often a savings on shipping, over shipping them separately.
You can also use the multiple
item order link at the top level web page.
You can click on the "Buy Now" buttons above to order on-line
using the PayPal service. If you have an account already set up on
PayPal, you can just use it as-is, if you don't have an account set-up,
you can do so on-line while ordering. You can use credit cards,
electronic funds transfers and other sources for the funds as desired.
Sure, 4Crawler Offroad can make single shims, cost depends on width, a
2" wide standard width single shim costs $18.00, a custom width
single shim costs $30.00. Common use is on Dana 44 front axles with
relocated long side spring perch, short side perch is cast into the
axle/differential housing. Contact
4Crawler Offroad for details.
In a spring-over-axle configuration, adding lift blocks does move the
center of the axle farther away from the leaf springs. Since one of the
leaf springs jobs is to resist the torque reaction of the axle to the
tires in contact with the ground, moving the axle farther from the
springs will increase the leverage of the axle on the springs. This can
increase the likelihood of axle wrap, which is a condition where the
axle causes the springs to twist into an "S" shape, arching
up in front and down in back, due to the axle torque. Whether this is a
problem or not depends on the weight and engine power of the vehicle,
the stiffness of the springs and the presence or absence of some sort
of torque-countering device like a traction bar, kicker shocks or
anti-wrap leaves. The taller the block the more likely wrap will occur.
Sure, if you need a tapered shim for another application, feel free to
contact 4Crawler Offroad for a quote. For example, tapered blocks/shims
have been designed and machined for bumper and radiator mounting
applications. Cost will depend on complexity and size of the part
Sure, no problem. Simply order the combination of a shim and lift
blocks as needed to make up the height of block you want. The shim will
typically be 1/2" center thickness, so account for that in the
overall block thickness. For example if you wanted a 1" tall,
6° tapered block, order a 6°
shim and a 1/2" tall
block. Or if you wanted a 2" tall block with an 8°
taper, order an 8° shim and a 1/2" tall block and a 1" tall block. Steel
blocks are available in any width, lengths to 6" long and height
increments of 1/2".
Or if you want an axle relocation plate combined with a shim or a
block, order the relocation plate and the shim or the block that you
want and we'll combine them into one, or you can keep the relocation
plate separate from the shim or block for ease of future changes. Just
let us know which way you would like them to be set up when you order.
The shim and block(s) will be machined and then welded together (for a
cost of $8.00 per welded lamination) and shipped to you ready to
install. If you want the block with a locating center pin, be sure to
order one pair of lift blocks with the center pin installed. Note that
a thickness of at least 1" (25mm) is required for a center pin to
be installed. This is because there needs to be a 1/2" deep hole
in one side for the head of your spring center pin to fit into and then
we need about 1/2" of material to secure the new center pin into.
Use the order button below to add the welding option to you block
and/or shim order:
Note that there are some considerations you might want to make before
opting for a welded block + shim. Keeping them separate gives you
flexibility in the future if you need to make further adjustments to
the drive line angles. Or if you make a change to the leaf springs and
need to eliminate or change the height of the lift block. Having the
block and shim separate lets you change either separately. While you
may think this is absolutely the only time you are going to change the
suspension on your truck, it may only be the first of many changes
you'll do over the years.
The classic answer is that it depends. It depends on how much extra
length your current center bolts have extending beyond the nut. And it
depends on how thick the shims you plan to install will be. How thick
the shims will be is a function of the angle of the shim and the length
of the shim. Shims up to about 4 degrees will typically be 1/4"
thick in the center, so if your center bolts have at least 1/4" of
exposed thread then you should be able to re-use them. Shims over that
angle can run up to 1/2" thick in the center. High angle shims can be thicker than
1/2" in the center, so factor in the thickness of the spring pack
plus the thickness of the shim into determining the length of the center pin/bolt.
As the name implies, the center bolt holes is typically drilled in the
center of the shim to allow either the shaft of the center bolt/pin (for a bolt-on shim) or the head of the center
bolt/pin (for a weld-on shim) to fit. However,
some applications require a hole that is not located in the center. If
this is the case, specify the center bolt hole location along with the
other shim specifications in the "Special
Instructions to Merchant" field of the order form. A
non-center hole is often required where the spring perches on an axle
have been redrilled to relocate the axle forward or backwards. And in
some cases, you may have an axle where the spring perches have multiple
holes in them to allow for several different axle locations. Often this
is done with something like a relocation
plate. If this is the case, the shims can be ordered with
additional center holes, as noted below:
And of course, you are more than welcome to order shims with no holes
at all and then you can drill hole(s) wherever you want.
When specifying an off-center hole(s), be sure to be clear about
referencing the hole location.
Examples of some imprecise descriptions are:
Hole offset 1" forward of the center (we don't know which end of
the shim you will be placing in front)
Hole 1" from center (which direction off of center?)
Hole 1" from the back (or front) of the shim (again, we don't know
which end of the shim will be in front)
So specify the hole is offset from or toward the thin or thick end some
examples would be center hole offset 1" towards the thin end or
hole 1" from the thick end
Also, hole locations are always given to the center of the hole, not
For example, some Ford pickup models use a non-standard leaf
spring/spring perch with two 1/2" center pins spaced 40 mm apart.
So instead of a single hole in the center of the perch, there are two
1/2" holes 20 mm forward and 20mm back from the center of the
spring perch. These spring perches are typically 3" wide x 5"
long. Note that some other F-150 customers (one with a 2007) have
reported needing 3/4" with a +/- 3/4" (19mm) offset from
center. This may be a case where the customer was wanting to slide the
heads of the center pins through the shim instead of removing those
bolts and sliding the shank of the center pins through the shims, as
discussed in the bolt-on vs. weld-on FAQ.
Another customer with a 2018 F-150 reported a pair of 1/2" holes,
one centered and the other 40mm offset to the thin end.
Also, if you get the hole spacing wrong and need an additional hole
drilled in a new location, this will be the same cost as drilling he
initial offset hole. You can return the shims to us with the new bolt
hole location marked with return postage and $10 for
redrilling/repainting and we'll modify it for you.
So be sure and confirm which size and spacing of holes that your truck
requires prior to ordering.
U-bolts need to be properly torqued. You should consult your vehicle
manufacturers recommendations, if that is not possible, then the
following can be used as a general guideline.
U-bolt Torque (from Rancho)
3/8" (10 mm)
1/2" (12 mm)
9/16" (14 mm)
In the above image, you can see how u-bolts are specified.
A is the inner diameter of the u-bolt itself (not measured at the
center of the bolt ends).
It corresponds to the maximum size axle tube it can fit over.
D is the diameter of the threaded bolt end.
Note that since most u-bolts use rolled threads, the un-threaded
portion is likely to be a bit smaller in diameter than the threaded
portion, due to the thread forming process pushing metal out to form
L is the length of the u-bolt, measured from the inside of the
"U" to the end of the bolts.
It usually needs to be longer than the total of the axle tube diameter,
the height of the spring perch, the thickness of the spring pack and
spring plate and still leave enough length for the washer and nut to
fit on top. U-bolts usually have an extra long threaded portion (which
is often specified) that allows them to fit a wide variety of heights
and then be cut to length.
If you find the nuts bottoming out on the u-bolt threads, you can stack
a few hardened Grade 8 washers under the nut to gain some height.
Finally, the shape of the end of the u-bolt can be specified, the two
common types are round and square.
Block the wheels and jack up the frame and put jack stands under it.
Remember safety first. This will take the weight of the truck off the
axles. You have to unbolt both sides before adding the shims. Unbolt
the u-bolts carefully. If you did not take enough weight off the axle,
the springs will ride down the u-bolts as you turn them. If that is
occurring, jack the frame up a bit higher. Once the nuts are off the
bolts, pull the bolts and plate. Now your springs are connected to the
frame at the rear perch and the front shackle. The springs are
disconnected from the axle.
For a spring-under axle setup, if you lower the frame, the axle will
stay put because it is resting on the jack stands. The springs will
pull away from the axle a few inches. For spring-over axle, you can
raise the frame a bit for added clearance.
See this FAQ section for details on how to orient
Clamping Leaf Springs
For a bolt-on shims:
Use C-clamps on your springs ahead and behind the spring perch (see
image above), clamping all the leaves securely. This will keep the
spring pack from fanning out when you take the center pin out. Next,
remove the nut on the bottom or top of the center pin. If the center
pins are damaged, you might have to replace yours, or if there is
insufficient excess length to accommodate the new shim. Put the shim in
between the springs and perch (make sure the head of the center bolt is
in the machined pocket in the shim) then install the old (or new) new
center pin in and put the nut on. Pull it tight, but make sure your
shim and spacer stay lined up. If you notice a slight height difference
in the 2 shims, you can check the ground to wheel well arch heights on
both sides of the vehicle and note which side is higher. For a
spring-over-axle setup, place the thinner shim on the higher side and
the thicker shim on the lower side of the axle. For spring-under-axle,
it's the opposite arrangement. This will help to level out that end of
the vehicle as leaf sprung vehicles are rarely perfectly level.
For single shims:
If installing a single shims, for example on a Dana 44 front axle w/
rotated knuckles, you should try to align the hole in the shim with the
hole in the other spring perch (that has been relocated on the axle
housing) to ensure the center holes remain lined up. If you just align
the center hole on the cast perch with the center hole on the shim, the
angle of the shim will "push" the hole forward or back,
depending on the shim orientation.
For a weld-on shims:
Place the shim on top of the perch, align the center bolt holes with a
spare center bolt head or something of similar diameter. Then place
weld beads on the thick end and sides as needed.
One option with weld-on shims is that you can make small adjustments to
the angle prior to welding them on using thin pieces of sheet metal
under one end or the other. On a 5" - 6" long shim, adding
0.010" thick stock (roughly 32 ga. or 0.25mm) with alter the angle
by about 0.1 degree (up or down depending on where the metal is
inserted. So if you are trying to dial in an exact angle, just tack
weld the shim in place, measure or test drive it and if you need to
make an adjustment, grind out enough of the tack welds to slip in some
shim stock, thin end will reduce the angle, thick end will increase the
angle. Then tack the shim in place and retest. Repeat until you get it
dialed in then weld it out, trapping the shim sheet metal in place.
For tapered blocks:
Slip the block in between the springs and perch, ensuring the pressed
in pin engages the hole in the spring perch and the head of the center
pin engages the hole in the block.
For axle relocation plates:
You may also need to drill new holes in your spring/u-bolt plate to
allow room for the end of the center bolt/nut to protrude from the
spring pack in the new location. The relocation plate will provide the
new hole in the spring perch for the head of the center pin, but if the
u-bolt plate also has a hole for the end of the center pin, it'll need
a new hole in it as well. You'll need to drill approx. a 5/8" (16
mm) dia. hole for the center pin nut to fit in. A stepped drill bit
(1/2" - 1" w/ 1/16" steps) works well for this is you
need to buy a bit larger than 1/2" for the job. That way you can
just keep enlarging the new hole until it is big enough to clear the
end of the center bolt. And, to be honest, you may be able accomplish
the same relocation by also drilling a new hole in the spring perch
without needing to purchase the relocation plates. One issue you may
run into with re-drilled perches is that there may be one or more
existing holes in one or both perches that may be close to where you
want to drill. Short of welding those holes closed, you'll have to
adjust your relocation holes to match any existing holes, if possible.
The relocation plates offer the advantage if being able to move the
center pin holes forward or backward wherever you want them. The
relocation plates are held in place by their pressed in center pins
fitting into the spring perch center hole and then the spring pack
center pin head fits into the hole in the relocation plate and finally
the u-bolts hold the spring to the plates to the perches. You can weld
the plates to the spring perch if desired, but that is not required.
Lower the frame back down (or up) until the center pin pops into the
hole in the perch. You may have to push and pull on the tires/axle a
bit to line the center pin up correctly with the hole in the spring
perch. Then, put the spring plate back on with the u-bolts back in. You
should inspect your u-bolts and if the threads are damaged or the bolt
appear stretched or fatigued, consider replacing them. You may also
need to replace them with longer bolts depending on the thickness of
the shim/block. New u-bolts are relatively inexpensive and reusing them
is often recommended against. After re-installing the u-bolts, torque
to the factory specifications (or use the table above). Check to make
sure everything is lined up. Push and pull on the axle to make sure it
is secure. Lower your frame back off the jack stands. Take it for a
test drive. Go slow and listen for odd noises and then re-check the
u-bolt torque after approx. 100 miles.