Marlin Crawler: Cheap Tricks

Visitor # 67767 since 28.AUG.2001

Here are some cheap tricks and tips I've found with my Marlin Crawler transfer case:

• The facts
• Driving Experiences
• Caveats
• Gear oil change for a Marlin Dual transfer case
• Short Throw Shifter installation
  
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The Facts:

My Marlin Ultimate Crawler (s/n #263) consists of a dual transfer case in which a 4.70:1 gear is installed in the rear transfer case. The front transfer case reduction unit (or crawl box) retains the stock 2.28:1 low ratio. The front crawl box is sandwiched between the transmission and the actual transfer case and it is 6.5" long. Only the high-low gear range is retained in the crawl box, the front drive part is removed. With the dual case, the front drive shaft is lengthened 6.5", which allows for longer wheel travel. In the rear, the shaft is shortened by the same amount. With a dual transfer case, you effectively have a 4-speed transfer case (see table below) and you gain a 2-Lo range (without having to unlock the front hubs) by putting the crawler box into low and shifting the transfer case between 4H and 2H.

With a Marlin Ultimate Crawler (dual transfer case), 5.29:1 R&P gears, overall crawl ratios work out to:

Final Drive Ratios (lower-than-stock)

Front	Rear	1st	2nd	3rd	4th	5th
1.00:1	1.00:1	20.9	11.3	7.3	5.3	4.5
2.28:1	1.00:1	47.7	25.8	16.7	12.1	10.2
1.00:1	4.70:1	98.3	53.2	34.4	24.9	21.1
2.28:1	4.70:1	224.1	121.4	78.5	56.7	48.1

To put this in perspective, take a typical engine idle speed of 800 RPM and using 33" tires with the above gearing, your speed is about 29 feet/minute, or less than 1/3 MPH!

If you are contemplating adding a dual transfer case to a 4Runner with the factory center console/rear heater (as I have), you'll have a few extra considerations.

1. First, the rear transfer case shift lever will come up through the front fo the console, where the rear window and wiper switches are located. You will need to move them someplace. Mine were initially moved up a few inches, but later I relocated them onto the dash.
2. The rear shift lever will probably need to be modified for short-throw operation. This is because there is limited room in the center console cutout. Marlin has a kit to do this.
3. The insertion of the crawl box pushes the output flange of the transfer case back 6.5", causing it to sit right under the rubber hose connections to the rear heater core. If you don't have at least a 1" body lift, you may need to re-route the hoses. With a 1" body lift (like I have) it is still pretty close, especially after I replaced the factory molded hoses with a straight section. So close in fact, that when my front engine mounts broke, the companion flange lifted just enough to abrade the rubber on the hose. Also, after converting my rear driveshaft to a CV-style top joint, the CV flange projects a bit beyond the companion flange.
   1. I decided it was time to fix this problem once and for all. So I did a "heater lift". I cut two blocks of wood, 2" tall, to fit under the heater core supports, and installed some M6x60 bolts in place of the stock bolts, to lift the heater and center console 2".
   2. This has a number of side benefits;
      1. Firstly, the upper hose connections are now much easier to make up from inside the cab instead of underneath the floor.
      2. Secondly, coupled with my 1" "seat lift" it raises the padded arm of the console to the right height to rest my right arm on. Before, it was about 2" too low and now it is just right.
      3. There is now a nice 2" clear space under the console that I'm sure I can put to good use!

Driving Experiences:

A few things I've noticed about driving with a Marlin Crawler:

• With the 4.70 gears engaged, there is much more play in the drive line. I find it most noticeable in rocky, flat trails where the engine alternately switches from driving to braking the wheels. I imagine some of this comes from the Detroit lockers I have, a 200K+ driveshaft, but it is *worse* in 4.70 than in 2.28 range.
  • In any situation where you are going down drop-offs, I find riding the brake as the wheels go over drop off is crucial. Otherwise, there seems to be a moment of free fall as the driveline unloads then re-tensions on a new tire. This too, is partly due to free-play in my lockers, but it is worse in 4.70 than in 2.28 gear.
    • Nice thing now is that in low-low-1st, no amount of braking can kill the engine!
  • A stock dual transfer case would be an alternative to this problem as you would get a low-low range of 5.19:1 and a 108 crawl ratio (w/ 5.29s).
  • I imagine my engine and transmission mounts are a bit sloppy (200K+ on the originals), so I'll be replacing those shortly and probably will use mounts on both the crawl box and transfer case like Jay Kopycinski did.
• The 4.70 gears are noisier than the 2.28 gears. There is a distinct whine that sounds kind of like a turbo.
• With my 22RE engine, I find it will stall in low-low-2nd gear at idle (121:1) but will not stall in low-low-1st, even up a steep hill w/ brakes applied (why is this important? - see below).
• I can now get the front TrueTrac differential to lock up using brake biasing.
  • The TrueTrac is a gear driven limited slip differential, not a true locker. It functions by the internal worm gears binding up and transferring torque between the wheels before spinning begins. The TT has a transfer ratio of ~3:1, meaning up to 3x the torque on the slipping wheel can be transferred to the gripping wheel. This is fine until a wheel is in the air (when 3x nothing is still nothing!). To compensate for this, brake drag can be applied to mimic grip, thereby transferring torque to the wheel with grip. In practice with my 22RE and stock gears, I found adding brake drag while crawling up a steep hill would simply kill the engine.
  • Now its all different. On the Toy4x4 Rubicon '98 trip at the top of Cadillac Hill, I was crossed up with the rear diff. hung up on a rock. I had three wheels spinning (including the front wheel in the air). Letting the engine idle in low-low-1st gear, I began applying brake pressure and the vehicle slowly started inching forward, pulled along by the front wheel that was on the ground. It is a weird sensation to start moving by hitting the brakes! Granted, if I had a true front locker, I wouldn't have been hung up in that situation, but the TrueTrac is *so* nice in the snow, that this quirk is worth living with.
  • I find that I can only get this technique to work if I'm below about 75:1 crawl ratio, at least when climbing steep hills. What I find is that I end up killing the engine with the extra brake drag, when it is nearly bogged down due to the steepness of the hill. As I begin applying brake drag, once the front wheel with traction begins taking torque, that will stall the engine. At 75:1, I've got barely enough torque to handle the vehicle load plus the brake drag.
• I find that the Marlin gears have helped my driving in stock low range as well. I find I have a much better feel of the throttle and engine response and can now idle/crawl through stuff I once would have had trouble with. In fact on a recent trail run, I used 4.70 gears going in and 2.28 coming out. Granted I did stall a few times coming out, but it otherwise felt comfortable and in control.
• I've learned that the 22RE engine speed is fairly stable below about 1200 and above 2500 RPM. In between those speeds, I find it tends to surge when the load is decreased, such as when you drive up and over a rock (high load up, low load down). Therefore, try to pick a gear to stay in one of those RPM ranges. With 20 forward gears, there is always one or two to choose from.

Caveats:

With such extreme low gearing, a few cautions must be exercised:

• Engine torque can be multiplied nearly 5 times over stock. Combined with traction-aiding differentials, this can result in all this torque ending up on one axle. In low range I try to stay off the gas and let the engine idle whenever possible. After all, the reason you are in the low gear is to go slow, SO GO SLOW!
• Combine a lower than stock differential ratio with much lower than stock transfer case gearing and you have a potential problem when out of gear. If you try to coast with the clutch disengaged, it can be exposed to extremely high RPMs at even slow speeds. Even at just 3 MPH in low range, the clutch will be spinning at around 8000 RPM, which is enough to cause it to disintegrate.
• I found my crawler gears to be much tougher to shift than my old gears.
  • After a few thousand mile breakin and changing to some nice synthetic gear oil, made them shift much smoother.
  • Note, that shifting in and out of the 4.70 : 1 gear requires a full stop in most cases.
  • The 2.28 : 1 gear can actually be used with judicious double-clutching.
  • Also, the 4WD shift-on-the-fly feature only works if you have the front hubs engaged. I thought I had lost that capability after the Marlin gears went in, but I had the front hubs unlocked.
• I notice the 4.70 : 1 gears have a lot of slop. This is most apparent when you are on undulating terrain and alternating between driving and braking. For level and downhills, I try to stay out of the lowest ranges for better control.
• I found another Marlin low use, that is crawling in deep snow. It seems that if you turn the wheels slow enough to allow the snow to compact, you can go in deeper, softer snow than you can by churning through with faster wheel speeds. At 98:1 I was getting farther than I could at 48:1, but at 224:1, I just floated over the powder.
• Beware that the shortened rear driveshaft may lead to vibration problems. Ever since getting my dual case, the rear driveshaft has vibrated. I had it straightened and balanced, I aligned it and what not, but I still got vibration. The angle, even with my modest lift, was too much for a single-cardan shaft. So I ultimately converted to a double-cardan (CV) driveshaft. According to Marlin, most folks with the double case, ultimately end up with a rear CV driveshaft.
• Also, be advise that the added torque of the double case and crawler gears must come from someplace. That someplace is your motor and tranny mounts. With the stock tranny mount placement, the rear transfer case is hanging out 6.5" from the mount. I plan on fabricating a plate to allow me to use two tranny mounts for added support. Also, if your front engine mounts are worn, replace them with new one and carry the old ones for spares.

Gear Oil Change:

After about a 5000 mile break-in period, I decided it was time to change the lube to the Marlin cases. I opted to use 75-90W Mobil-1 synthetic gear oil. Those dual cases seems to really heat up with the mineral oil, the slicker oil seems to help out some. Also, with the added friction of the second case, I found that I picked up 1 MPG or so after changing to the synthetic oil.

So, upon close examination of a Marlin Crawler dual transfer case, I noticed there are two drain plugs but only one fill plug, (on the stock transfer case). It turns out the crawl box shares the same gear oil with the transfer case. To change the gear oil in this setup involves the following steps:

• Warm up the transfer cases;
  • A 10-20 mile drive should do it.
• Remove the fill plug and both drain plugs (one at a time unless you have a large drain pan).
  • If the plug on the crawl box is not drained, about a cup of old gear oil will remain there.
• Replace both drain plugs and fill both gear boxes through the rear fill plug (GL/5 grade oil).
  • Total gear oil required is approx. 1.7 qts. for the transfer case and 0.7 qts. for the crawl box.
  • Wait 5-10 minutes after the initial fill and top off the oil as needed.
  • For a proper fill, this should be done on level ground.

Rating:

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[Last updated: 22.March.2021]