OUR TOYOTA FJ40’S TRANSMISSION & T-CASE TURMOIL

Transmission & T-case Turmoil

While piloting Tim Toyota (the 1976 Toyota FJ40 Landcruiser we saved from becoming a permanent backyard ornament), we have been described as Homer Simpson-esque, comically bamboozling our way along a trail inadvertently smashing everything in, or out, of sight. We looked out of control and were going WAY too fast. During our last instalment we got the old V8 under the hood running properly and ready to hit the dirt, our problem now was the speed at which it chose to do so.

4.10:1 axle gears, a lackluster 3.55:1 transmission 1st gear ratio, and a deplorable 1.959:1 transfer case low range gave us… ugh, 28.51:1 crawl ratio. We needed to slow things down and gain some control on the trail before we started snapping parts or flipping over. How do we do this, and what is a crawl ratio?

A crawl ratio is the number of engine revolutions per wheel revolution. It is calculated by multiplying the transmission 1st gear ratio, transfer case low range ratio, and your axle gear ratio. Tire size has little

bearing on this, and remember that there is no “perfect” number for slaying trails - it is all about compromise. Too low and it will take you days to go a kilometre, too high and you will not have the control you should, and you can start overheating transmissions or burning out clutches. We typically like a ratio in the 50:1 to 80:1 range for mild trail runners and up to about 120:1 for our hardcore rigs. Any deeper is borderline ridiculous and you’ll have a lineup of frustrated wheelers plotting your death while waiting for you to finish a trail… you know who you are.

We like to drive our rigs to and from the trail, so our first course of action with any new rig is to determine what size tire we plan to run. This is the only point at which we care about tire size. Knowing this, and where our particular engine likes to run when on the highway, gets us a ballpark axle gear ratio. In our FJ40, we have a 4-speed manual transmission with no overdrive and a torquey small block Chevy under the hood. The 1:1 4th gear ratio and 4.10 axle gears give us a cruising RPM of about 2600 with our 35” tires at 110 kph. This number can be calculated, but we find it is best to use one of the available online charts. Remember to use the ACTUAL tire diameter, not the number on the side! Modern automatic transmissions have lock up torque converters so you can use the top gear ratio, for old school autos, plan on some slippage in the 15% to 30% range.

We are happy with the 4.10:1 axle gears even though they are a little on the low RPM side. We’re not worried about over revving the engine of our off road rigs on the highway, and have a hard time justifying changing gears for only a few hundred RPM difference. So we’ll leave them for now, as swapping from 4.10 to a 4.56 will hardly be noticeable.

Our next stop in the drivetrain is the transmission. As we mentioned, automatic transmissions have some slippage when crawling in the woods, so we normally add 40% or more to the 1st gear ratio of an auto to get the manual transmission equivalent. An auto (TH400)

with 2.48:1 1st gear will behave like a 3.47:1 geared manual transmission (2.48 X 1.4) and we will use these numbers for crawl ratio calculations. Transmission swapping can be an expensive endeavor and seeing as we had recently rebuilt the H42 unit in our FJ40, we were reluctant to change it.

With our respectable axle ratio and our transmission happily in place, that only left our transfer case available to make changes. The aluminum unit is not known for longevity, or strength, and ours sounded like a badger in a blender. The lack of gearing was the last straw and we quickly called up Advance Adapters, but not for one of their famous and sought-after Atlas II T-cases, no, we called for their lesser known, but equally tough Orion units, with a 4:1 gear ratio designed specifically for the Land Cruisers and offset differentials like our FJ40.

Factory Toyota FJ’s of this era came with both differential center sections offset to the passenger side, unlike most 4x4 vehicles made in the last 30 years where the rear differential is centered and the front axle is offset. The cast steel Orion emulates this and is a direct replacement for many ‘63 to ‘80 Land Cruiser’s ailing from weak and under geared T-cases. The made in America Orion utilizes many of the factory Toyota pieces saving some money and adds some much needed beef to the rest. Thicker castings, more webbing, larger idler shaft, high-quality bearings and seals, are just some of the upgrades with bonuses like no need for driveshaft mods, speedometer integration or even emergency brake changes. They all bolt up just as the factory intended.

The original transmission and transfer case had to be removed in order to complete the swap as some of the original pieces had to be reused. We took this opportunity to install our newly rebuilt transmission, and install the new Centerforce clutch and bellhousing that we received from Advanced Adapters (AA) and Summit Racing. Originally Tim was saddled with a janky, and unsafe homemade aluminum adapter that was sandwiched between a Chevy bellhousing and the Toyota transmission. The lack of proper alignment, combined with the incorrect pilot bushing, is what had taken the original transmission out of commission. Proving once again that it’s easier to do it right the first time, than do it wrong twice.

At the end of our shop time we were gifted with a crawl ratio of 58.22:1. Perfect for hauling ass down the highway and crawling up some pretty difficult trails all in the same rig. The smooth Centerforce clutch sent power seamlessly and reliably down the line through our whisper quiet transmission, and on to the much stronger, quieter, and more reliable Orion transfer case. On the trail, the deep gears allow us to effortlessly crawl over obstacles, and overall make the driving experience lightyears ahead of what we had.

Summit Racing Equipment – www.summitracing.com Advance Adapters – www.advanceadapters.com Centerforce Clutches www.centerforce.com

1 The standard, cast aluminum Toyota transfer case (right) is not the most durable of units. Ours howled like an air raid siren until it went “bang”. The Orion transfer case is essentially a factory looking unit on steroids with a 4:1 low range ratio and bigger internal components all designed to take the place of the original.

2 Shown here are all the pieces you will need to replace your factory case with a sturdy, cast steel Orion transfer case from Advance Adapters.

3 The folks at AA must have known how cheap those of us wheeling vintage iron are, and utilize many original components. We tore apart the old case to salvage what we could in order to build the Orion.

9 It’s very nice to see high quality, brass thrust washers included in the kit.

7 Without a large, flat surface to press against, great care must be taken. Gentle taps, patience, and a little aviation sealant help.

6 Tapping home a bearing within an aluminum housing takes great care as in this front output housing. Make sure the bearing goes in straight and smooth to avoid galling. A press really is best in these circumstances.

5 For metal edged seals as shown here on the rear output shaft, a light coating of aviation sealant will keep leaks at bay.

4 First step is installing many of the seals. We highly recommend finding a proper seal and race driver set as shown here, and also know the procedure for each style of seal. The rubber seal shown required no additional sealant, but a light skim of oil helped tap it into place.

8 We like to pre-lube bearings such as this idler gear caged roller bearing set. The engine assembly lube from Amsoil is great as it sticks in place and hold onto the parts until proper running lubrication can wash it out.

13 We checked gear clearances against a factory manual many times during the build. If you detect a measurement that is out of spec, stop and inspect your work and parts, as now is not a time for “Good Enough”.

11 With all idler components in place, the new 38mm main shaft is installed. Notice how much bigger it is compared to the original, as well as the wear on the original shaft from excessive loads.

10 The Amsoil assembly oil helps the thrust washers stick to the case wall as the idler gear cluster is put in place.

12 Pressing the new bearing on can be done with a hammer, but a proper press is much more efficient and lessens the risk of damaging the components. If you are performing this kind of work often, it is well worth the cash to have one in the corner of your shop.

14 AA includes a piece of tubing to help press the final output shaft bearing on. The shaft and gears must be installed in the case, and then you can press the bearing in.

18 With the Orion essentially “built”, all that was left was to install the new input gear and bolt it to the transmission.

20.3clutch The Centerforce and pressure plate are very well weighted and set up for mating Chevy power to the Toyota drivetrain. The pedal is light and easy to modulate over rough terrain, and provides plenty of renowned Centerforce holding power.

16 The preload itself is adjusted with differing shim thicknesses.

19 With the proper spacers and bearings in place, we just had to “stake” the nut after torqueing the nut down. A simple cold chisel will do, as we just want to prevent the nut from backing off.

20.1end Moving to the other of the transmission, we installed our new Advance Adapter conversion bellhousing to adapt our Chevrolet V8 to the Toyota H42 4-speed transmission using an original fork and bearing retainer. AA includes all the hardware needed and specified the proper clutch to use.

15 With all of the output assembly installed, proper bearing preload needs to be set. This is done by measuring the force needed to turn the shaft in the housing with a torque meter such as this Wright unit that we’ve had for years.

20.2new AA also included a pilot bearing for the Chevy motor. Unlike the sintered brass unit, it is a seal and caged roller bearing designed to provide years of service.

17 Once the proper preload is set, more aviation sealant on the paper gaskets is used to protect against leaks.

26 Some shifter adjustment may be required after installation. Remember to take it easy on the gears and clutch for the first few hundred kilometers and change the oil for a long future of wheeling fun.

24 With all the rod ends and components in place and aligned, we just had to weld the components together.

22 Engraved shifter handles will help ensure we don’t grab the wrong handle… hopefully!

21 Last on our docket was to assemble the new twin stick shifter assembly. This will allow us to run in 2WD high and low range which is very handy on bumpy trails not requiring 4 wheel drive.

23 The only internal component that needs to be modified is the front assembly shift fork and the procedure is well outlined in the manual.

25 After a coat of paint, the assembly was ready for installation.