Marlin Crawler Cheap Tricks


Marlin Crawler: Cheap Tricks

Visitor # 66950 since 28.AUG.2001


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


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


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:


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[Last updated: 22.March.2021]