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 loads.
Below, you can see a few versions that 4Crawler Offroad has produced over the years:
Below are some examples of various shim styles, tapered blocks, relocation plates:
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.
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.
All our shims and lift blocks are proudly designed and manufactured in the USA.
4Crawler Offroad can machine solid steel axle shims, custom angles, 1°-12°, made to your specifications:
Style : Select style Bolt-on Weld-on
Hole : Hole location Centered Custom, use: note to seller/e-mailor via e-mail No hole
Hole Size: HoleSize Default hole size 5/16 in. 3/8 in. 7/16 in. 1/2 in. 9/16 in. 5/8 in. 3/4 in. Custom, use: note to seller/e-mailor via e-mail
Angle: Angle 1° 2° 3° 4° 5° 6° 7° 8° 9° 10° 11° 12° Custom, use: note to seller/e-mailor via e-mail
Length: Length 3.75 in. 4.00 in. 4.25 in. 4.50 in. 4.75 in. 5.00 in. 5.25 in. 5.50 in. 5.75 in. 6.00 in. Custom, use: note to seller/e-mailor via e-mail
Hole Size: HoleSize Default hole 5/16 in. 3/8 in. 7/16 in. 1/2 in. 9/16 in. 5/8 in. 3/4 in. Custom, use: note to seller/e-mailor via e-mail
Style: Select style: Bolt-on Weld-on
Angle: Angle 1° 2° 3° 4° 5° 6° 7° 8° 9° 10° 11° 12° 13° 14° 15° Custom, use: note to seller/e-mailor via e-mail
Length: Length 3.75 in. 4.00 in. 4.25 in. 4.50 in. 4.75 in. 5.00 in. 5.25 in. 5.50 in. 5.75 in. 6.00 in. 6.50 in. 7.00 in. 7.50 in. 8.00 in. Custom, use: note to seller/e-mailor via e-mail
Width: Width 1.75 in. 2.0 in. 2.125 in. 2.25 in. 2.375 in. 2.5 in. 2.75 in. 3.0 in. Custom, use: note to seller/e-mailor via e-mail
Hole Size: HoleSize Default hole size 5/16 in. 3/8 in. 7/16 in. 1/2 in. 9/16 in. 5/8 in. 3/4 in. Custom, use: note to seller/e-mail
Hole : Hole location Centered Custom, use: note to seller/e-mail No hole
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 order form.
Style: Select style: Bolt-on Weld-on No center hole
Typical center pin dimensions, may vary:
The unthreaded shank length will be the difference of the bolt length and the thread length.
Center Pin Ordering: sold in pairs (i.e. 2 bolts/nuts)
Size: Select size: 5/16 x 2.25in. 5/16 x 3.0 in. 3/8 x 3.0 in. 3/8 x 3.5 in. 3/8 x 5.0 in. 7/16 x 4.0 in. 1/2 x 4.0 in.
Below are some commonly asked questions along with answers. Please take a minute to browse this list and see if it answers your questions. If not, feel free to contact me...
If this is all too confusing to figure out, 4Crawler Offroad will be more than happy to consult with you on your specific application.
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.
In the above image, you can see how u-bolts are specified.
If needed, 4Crawler Offroad can special order a selection of replacement Grade 8 u-bolts. They include lock nuts and washers and run approx. US$25-30/ea. depending on size. Contact 4Crawler Offroad for more information.
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 tires, and 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.
For a bolt-on shim, you can put a C-clamp 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.
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.
Toyota e-brake extension installation.
(Contact 4Crawler Offroad if interested in more information on any of these items)
Visitor # 257313 since 13.AUG.2001
[Last updated: 11.February.2021]