RUST BULLET AUTOMOTIVE



Tech:
Marlin Crawler for Automatic Transmissions

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Author: Phil Johnson March 2000 Editor: Scott Wilson

7th Annual 4Runner Jamboree

'Slow is better, Marlin Crawler is best,' is what I heard when talking with other 4Runner owners at my first trail run, the 1999 4Runner Jamboree. I knew very little about wheeling when I started the weekend, but by the time I left, I had made some new friends and was planning the first of many modifications! After hearing testimonies of Marlin's customers, and seeing their crawlers in action, I knew I wanted a Marlin Crawler in my truck, a 1995 4Runner with an automatic transmission. I quickly learned that I could not have a crawler because they would not mate up to my automatic transmission. Everyone I asked told me "you can't put Crawler gears in an automatic." Marlin himself was even skeptical.



At Marlin Crawler's shop

When someone tells me I can't do something, I get more determined to do it, or at least fully understand why I can't do it. This "can't do" caused me to spend many hours researching Toyota automatic transmissions and transfer cases, and before I was done this "can't do" would be a "can do, and it's done." This research ended with me swapping my automatic transmission for a newer model, and installing a Marlin Crawler Ultimate dual transfer case. I took my research to Marlin who was also working on this idea. Together we solved the remaining engineering problems of swapping the newer automatic transmission into my truck, and with Marlin's new adapter plate, installed an 'Ultimate' transfer case into my truck. Many thanks go to Marlin, David and Aaron at Marlin Crawler who helped make this happen.

This article is divided into two parts. The first part details the automatic transmission swap. The second part covers the Ultimate Crawler Dual Transfer Case installation.

A340H to A340F Automatic Transmission Swap

The only way to have lower gears in a Toyota transfer case is to use the old gear-driven 4 cylinder transfer case. I had to find a way to mate one of these transfer cases to the automatic transmission in my truck. My 95 4Runner started life with a model A340H transmission, which has an integrated hydraulic-actuated transfer case. The transmission and transfer case are designed to act as one complete system, and even share the same automatic transmission fluid. For all practical purposes the two cannot be separated. Research uncovered that Toyota makes one other 4WD automatic transmission, the model A340F. This transmission uses a manually-actuated transfer case that can be separated from the transmission. The transfer case used with this transmission is not a type that lower gears can be put into, instead it is chain driven. Some way had to be found to mate a 4 cylinder transfer case to the A340F transmission, and Marlin Crawler had the answer. Marlin Crawler created the solution, and he now offers an adapter plate to mount his transfer cases to the A340F transmission.

The A340H & A340F transmissions have nearly identical dimensions and share the same main case and bolt patterns. Both are electronically controlled 4-speed overdrive units. The fundamental operation of the two models is the same. The donor vehicle for my A340F transmission was a 1998 4Runner. I received the transmission, transfer case and torque converter from this vehicle. The transmission swap shown here should be the same for any 1996 or newer A340F transmission replacing an A340H in a 1995 or older V6 vehicle, 4 cylinder vehicles may differ.

Follow these steps to begin removing the A340H transmission: Disconnect the kick-down cable from the throttle body on top of the engine. Cut any cable ties bundling the wiring harness that runs across the top of the transmission and the kick-down cable running down the passenger side of the engine. Disconnect the wiring to the transmission & transfer case at three plugs near the bell housing on the passenger side. Take care not to damage the bell housing, wiring, temperature sensor, kick-down cable, oil pan or filler tube, as these will be transferred to the A340F transmission.

A340H & A340F Transmissions

Next, remove the bell housing and transfer case from the new transmission. Place the two transmissions side by side. Disconnect the wiring plugs from the old transmission. Cut ONLY the two wires that go to the solenoid on the transfer case of the A340H transmission (these have NO individual connector). On both transmissions, remove the temp sensors located near the bell housing on the passenger side. Install the old temp sensor on the new transmission using a small amount of Toyota FIPG (sealant).

Now remove both oil pans. On each transmission, disconnect the wiring from the solenoids and remove them. Install the solenoid wiring (connected to the entire harness) from the old transmission into the new transmission. Use a small amount of Toyota FIPG on the plug into the transmission case to prevent ATF leakage. Remove both kick-down cables and install the A340H kick-down cable on the A340F transmission. Install the A340H oil pan on the A340F transmission using Toyota FIPG.


A340H & A340F bell housings

Next, install the A340H bell housing on the A340F transmission. Connect the wiring plug to the neutral safety switch. Use cable ties to bundle the excess wiring up on top of the new transmission. Leave the two-wire plug for the speed sensor accessible. If necessary, install the shift lever from the old transmission to the new transmission. Remove the speed sensor from the tail housing on the new transmission, as well as the speed sensor rotor from the end of the mainshaft of the A340F transmission.

Remove and save the speed sensor from the tail housing on the A340H transmission. Remove the transfer case from the old transmission, so that the speed sensor magnetic rotor from the mainshaft of the old transmission (located just past the end of the main case) can be removed. This may require removing gears from end of the mainshaft. We obtained a used magnetic rotor from a core A340H that was already torn apart in Marlin's shop.

The speed sensor and magnetic rotor from the A340H must be installed in the new transmission. This requires some very precise machine work. It is not something that can be done with hand tools. Before the magnetic rotor can be placed in the A340F, it also must be machined. Marlin is creating a kit that will include a machined tail housing for the speed sensor and a machined magnetic sensor that will fit properly on the mainshaft. Look for this information on Marlin Crawler's web site in April, 2000.

The magnetic rotor must be placed on the mainshaft with the backside towards the main case and the magnet facing towards the rear. The magnetic rotor will fit on the mainshaft, but the backside must be machined just deep and wide enough to clearance the main case first. We used a small milling machine and an adjustable center bore to do the machine work.

Modified Tail Housing

Now the A340H speed sensor must be installed in the tail housing of the A340F transmission, such that the end of the sensor is pointed at the center of the mainshaft, 0.12" from the magnetic rotor. This is a critical dimension for the proper signal to be generated for the ECU. It is possible it would still function if the clearance was less, but certainly it should not be more than 0.12". The hole is drilled into the tail housing near the location of the existing speed sensor hole. This area of the tail housing is thick enough to hold the sensor. Once again, we used a small milling machine to drill the new hole and mill the face of the area at the hole so the sensor would sit flush to the tail housing. The existing hole was plugged with a slightly swaged 19/32 aluminum freeze plug and Toyota FIPG.


Speed sensor mounted in the machined tail housing

We installed the speed sensor in the new hole after the new transmission was mated to the dual case. This was to ensure that the sensor did not get damaged during the installation of the dual case.

The original shifter assembly inside the cab would not work with the new transmission. The shift linkage is on the other side and there is no way to accommodate the new manual transfer case shifter, or in my case, the Crawler reduction box shifter.

Old shift assembly

I chose a 1997 4Runner Limited shifter assembly to replace mine. It is designed for the new transmission and has a 4WD switch in the transfer case shift handle. The switch activates the 4WD solenoid on the transfer case. Right now this switch has no function on my truck, though later it will become my ARB switch.

Next remove the A340H shifter assembly. The wiring for the park lock solenoid, lamp and OD switch were all the same as in the old shifter assembly. I simply cut and spliced the connectors from my old shifter onto the new one. The wire colors were identical which made it an easy operation.


Floor Modifications

Place the new shifter over the existing hole and mark the floor where the hole has to be opened. Carefully cut the floor and re-fit the shifter until it sits flush to the floor. Check the alignment with the console in place to get the right placement. Mark the holes and drill. I used the existing bolts with nuts on the underside. This meant it was a two person operation to tighten them. Smaller holes with sheet metal screws would probably work and be a lot easier.

The new shifter does not seal the floor due to the different hole cutouts. I glued some 1/16 rubber to the underside of the new shifter and sealed the edges with silicone sealant before bolting it down. Then I went underneath and applied more sealant to ensure I had a watertight seal.


New console

I had originally planned to use the 1997 console piece that came with the shifter. Although it looked good, it didn't match well with my 1995 interior. I went to my local Toyota dealer and found that the original console for 1989-1995 4cyl 4WD AT Trucks was a perfect match and still available in the same color as my blue 1995 interior! This console is designed to fit together with my rear console and matches the color perfectly.

The 1997 shifter assembly is a little taller than the original. The console sits about inch high on each side. I used 1/16" black acrylic plastic to fabricate raised console mounts and cover the gaps.


Old shift linkage

The shift linkage for the A340H transmission was a lot longer than necessary for the A340F transmission. I shortened it to 10 3/8 inches eye-to-eye by cutting and welding. Be sure to keep the proper eye alignment and the adjustment section of the rod.

Mounting the new transmission to the engine was typical of re-installing an automatic transmission. Be sure to use the torque converter that comes with the new transmission. There are some differences in torque converters depending on engine, year and model of transmission.

The new A340F transmission is far superior to my A340H. It's shifts are stronger and more positive. I no longer guess if the transmission has shifted or not. With the rest of the drivetrain being direct gearing, I am getting more power to the rear wheels. After more than a week of daily driving, I also found that gas mileage increased 1.5 MPG with the new transmission and transfer cases.

Click HERE to go to the second half of this article, Installing a Marlin Crawler on an A340F Automatic Transmission.






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