Marlin Crawler for Automatic Transmissions

Http:// Short Cuts
Author: Phil Johnson March 2000 Editor: Scott Wilson

Click HERE to go to the first half of this article, A340H to A340F Automatic Transmission Swap.

Installing a Marlin Crawler on an A340F Automatic Transmission

Marlin's new AUTO kit

Marlin Crawler has developed a kit that allows the 4cyl gear driven transfer case, or dual case, to be mated to the tail housing of the A340F automatic transmission. This kit includes his brand new AUTO adapter plate, as well as coupler, bearing, and all seals you will need to mate the two cases.

The Dual Case Ultimate Crawler is two pre-1996, 4-cylinder transfer cases, with stock 2.28 gears in the front case and Marlin's 4.70 gears in the rear case. An 'Ultimate' mated with a A340F, with 4.88 ring & pinion will provide a crawl ratio of 146:1 and a total of 16 forward speeds. In addition, the dual case gives me a 2-Lo option by simply putting the front case in Low. See table below.

Xfer #1
Xfer #2
H H 1.00 X 4.88 13.66 7.47 4.88 3.46
L H 2.28 X 4.88 31.15 17.02 11.13 7.90
H L 4.70 X 4.88 64.22 35.09 22.94 16.28
L L 10.72 X 4.88 146.42 80.01 52.29 37.13

Inside the transmission tail housing, we replaced the existing bearing with one that snugly fits on the coupler between the transmission and transfer case. The coupler is drilled for an oiling hole just in front of the bearing. The oil comes from the end of the transmission mainshaft and flows inside the coupler to the hole. It is then slung out the hole into an oil slinger that brings it down to the bearing. From the bearing it flows back down into the back of the transmission oil pan. Inside the coupler is a plug to prevent the oil from flowing to the other side. On the transfer case side of the bearing there is a seal to keep the ATF out of the transfer case, and gear oil out of the transmission.

The original coupler was about 1/8 inch too long and would interfere with the adapter plate when we test fit it all together. A die grinder was used to clearance the fit. Marlin's AUTO kit will include a propperly-clearanced coupler. The dual cases were assembled first. The adapter plate was then mounted to the transfer cases, and finally, the dual cases were mounted to the A340F transmission.

Floor Modifications

The dual case required a new hole for the rear transfer case shifter, about 6" behind the normal location. I wanted a stock look and decided to have the shift lever come up in the small cup at the front of my center console. I drilled a small hole down through the center of the cup to locate the larger hole in the floor. Then I cut out the bottom of the cup, leaving about a 3/8 inch lip to attach a boot. A 3" hole saw was used to cut out the hole in the floor for the shift lever.

After all the drilling and cutting of the floor was complete, we moved the transmission and dual case assembly under the truck for final installation. The units fit as they should, without any problem. My original transfer case crossmember didn't line up well at all with where the transfer case mounts now were located. We found that an 85 4cyl crossmember fit with only a 0.5" offset from the factory frame mounting holes. I used a hacksaw and die grinder to slot the holes in the crossmember and now it bolts up like the original crossmember did.

Now all electrical, shifter, and oil connections were reconnected. There was no need to modify oil lines or wiring for the A340F transmission. Everything matched up as if the A340F transmission had been original equipment for this vehicle. I used cable ties on the wiring and kick- down cable where they go up the passenger side of the engine to keep them away from the exhaust. I also put a cable tie on the wiring where it crosses over the transfer case crossmember to keep it up and out of harm's way.

New console

The dual case shift levers had to be custom fit. My 4Runner has a 2 inch body lift and the rear shifter had very little room for shifter throw. The front shifter is offset from center to come up in the left side of the factory console. Marlin is an artist when it comes to custom shifters, he put a short throw kit on the rear shifter and fabricated extensions for both shifters. After about 2- 1/2 hours he was finally happy with the result. It had to be perfect, and judging by the results, it is!

Dual Cases Installed

The rear driveshaft was shortened and the front was lengthened to accommodate the new location of the 2nd transfer case. Since my 4Runner is still IFS (Independent Front Suspension), crossmember clearance was not an issue for the front drive shaft. In the future, I plan to put in a low profile crossmember with a skid plate. We added the proper fluids and started the engine. After a couple minutes, we shut it off and added more ATF. The transmission requires a lot of fluid when the torque converter is dry. Once everything was checked and re-checked, we pulled the 4Runner out of the shop for a test drive!

I am very happy with the results. The transmission and Marlin Dual Case Ultimate Crawler work great together. It has been the best modification I have done to my truck so far. While the job took considerable effort, we proved it is not impossible. It seems fitting that the first trail test of the dual case automatic will be the 2000 4Runner Jamboree this April.




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