[MR2] MKI tranny talk

[Marc Medina]

Or, you can do it the much easier way by simply swapping the shifter mechanisim as I did for my 6 speed conversion: www.marcmedina.com/6speed.html
   
  Marc 

Donald Chalfant <dkchal at datasync.com> wrote:
  http://www.wcengineering.com/articles/toyotatrans.html



A C-50 and a C-52 look very similar and they are very similar. They share 
many parts. The key factor is that a C-50 has a boss or hump for the starter 
motor on the front side of the transmission case. (The front side is away 
from the differential, or if looking at one on a car, the exhaust side of 
the engine.) On the other hand, the C-52 has two starter bosses, one in the 
front and one in the back. The normal 1.0 kW or 1.4 kW starter can be bolted 
in place on the front position under the exhaust manifold. The 1.4 kW 
starter from a supercharged MR2 can be bolted to the rear boss. I have seen 
C-52s that have the bolt holes already drilled and tapped for the starter in 
the rear position and I have seen others that need to be drilled and tapped 
but the mounting points are there.

C-50/C-52 Differences

Every C-50 and C-52 that I have seen that came from an AW11 MR2 had the 
4:311 final gearing. I have seen FWD units with both the 4:311 and the 3:722 
final gearing. The C-52s have some stronger parts. The 1-2 shift fork was 
upgraded and is interchangeable. The C-52 has a larger diameter input shaft 
where fourth gear rides on its bearing and hence has a different bearing and 
gear. Syncros have been upgraded over the years and the later ones are much 
better. The later 1-2 syncros can be directly dropped in to an early C-50, 
but third and fourth require some additional parts to make the swap. I don't 
think the fifth gear has ever changed.

The C-150 Transaxle
Be wary of the C-150. At first glance it appears very similar to a C-50 and 
to the untrained eye, it could be passed off as one. Other than a few small 
bolts, this cousin to the C-5X series shares few parts. This transaxle is 
slightly shorter than a C-5X and has a smooth finish to the case and bell 
housing. (The real C-5Xs have strengthening ribs down the bell housing.) The 
C-150 is smaller and lighter weight, all the gears are a little narrower 
than the C-5X so the input and output shafts are shorter, and the 
differential is a puny little paper weight.

Using a FWD Transaxle in a RWD Car
Or, better stated, "converting a FWD transaxle to RWD setup by moving the 
shift selector shaft."

First, if you can locate the correct transmission, do it! If you cannot, the 
process can be done, but you are better off just rebuilding your 
transmission.

In order to do this, you will need the Genuine Toyota "Big Green Book." You 
will also need some gear pullers, some bearing drivers, and a very good 0-15 
in-oz dial-type torque wrench. (Read "expensive 0-15 in-oz torque wrench" 
and, yes, that does say inch-ounces.) You will need pretty much all the 
tools that are stated in the BGB about rebuilding a transmission, along with 
a selection of differential pre-load adjusting shims.

Let's presume that you have a good C-50 FWD transmission. You will also need 
a RWD C-50 transmission to get the case center section, shifter selector 
shaft, and housing cover. You will disassemble the FWD transmission and the 
RWD transmission. I could go through all the details but it's all in the 
BGB. When you get the first transmission apart and the center section off, 
you may think that you're almost done. Tear down the second transmission, 
swap cases and you're finished, right? There is a slight catch.

It's not that simple. The center section and bell housing section also make 
up the differential housing and each half has a bearing race for the 
differential. Because you are going to be using parts of two cases that 
weren't originally used together, you must re-set the pre-load of the 
differential. (If you chose to skip this step, I hope you have alternate 
transportation because your "new" transmission won't last long.) The 
pre-load is adjusted by selecting shims that sit under the outer bearing 
race of the differential. This is normally done by hand at the factory and 
now because we are using different case halves, we will have to adjust it 
again.

The procedure is given in the BGB, but I'll outline it here. First, tear 
down the entire shifter mechanism from the gears, then remove the shifters, 
then remove the input shaft and output shaft as a set. Now you just have a 
differential sitting on the bearing in the bell housing case. You would now 
assemble the new case center section with no gears, just an empty shell. You 
put the case all together, bolts and all, and check the pre-load with the 
torque wrench and a special adapter. If the torque is too low, or too high, 
you tear it all back down and change the bearing shim. You continue to 
assemble, measure, tear down, assemble, measure, etc. until you get the 
correct pre-load. It still takes me at least three to four cycles to get it 
"spot on." Once you have it adjusted correctly, you can tear it down again, 
install the input and output shafts, shifter rails, shifter forks and such, 
then assemble the center section. Finish up with the rest of the parts and 
you're done... finally. Now you can put it in your car.

Changing the Final Drive Ratio or Adding an LSD to a C-5X Transaxle
There are several ratios available, from 3.56:1 to 5.166:1. Toyota used the 
4.312:1 and the 3.722:1 in production vehicles for the US and I'm told that 
the 3.56:1 was used in production somewhere, but I have yet to see one in a 
5-speed transmission. I have seen it in a C-40, but due to the output shaft 
differences, it won't fit a C-5X. TRD also makes some gear sets for the C-5X 
transaxles but they are cost prohibitive.

The addition of an LSD is excellent for the track and street. I personally 
don't like clutch-type units and am biased towards the Quaife or TRD helical 
gear units. They both give phenomenal performance.

Installation of an LSD is not an easy task and requires complete tear down 
of the transmission as outlined above and it is detailed in Toyota's BGB. 
This is not a task for a newcomer and only the most experienced shops can 
perform this type of work. If you would like a quote on the installation of 
an LSD in your Toyota transmission, contact us.


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