rear diff question
 

if ur front diff is 3.90 and ur rear is 4.11, will it cause ur tranny to overheat and even smoke? :(

I just got a tranny installed but i think the rear and the front diff ratios don't match.

No if you remove the driveshaft. This is the only way you could drive with different ratios in front/rear diffs. Unfortunately it disables the AWD :D

You can plug in the FWD fuse (or is it remove the FWD fuse?), but this is a short-term solution, enough to get you back to the shop that installed mismatching diffs.

yea..

i put the awd fuse in..

but awd is still working..

it says fwd, but when i put it on the lift and checked..all wheels still move..:(

This is bad
 

You are definitely causing damage to certain components within your drivetrain. You need to get this fixed.

Todd

Subaru AWD in automatic transmission is a multi-plate wet clutch - there is still some friction even when clutch is disengaged. This might explain why rear wheels still turning even in the FWD mode.

There should be little torque though passing to rear wheels.
I do not remember exactly, but there some issues if you leave it in FWD mode permanently - something related to fluid circulation and lubrication.

3.90 vs 4.11 is approx 5% speed difference - way to much for transfer clutch to handle. One crazy idea is to try to get a different diameter wheels (5% more on the back) to compensate for the different ratios. Wouldn't do it on my car though.

well i am not driving till i can get it fixed, yesterday i only drove it home from the garage which was about 10 km.

Soon i will have my mkII supra..:) and will no longer have to worry about overheating tranny's

ok..some new news...i called the subaru dealership and gave them the vin i got the tranny out of and they said the ratio is 4.11. This makes no sense, what else could cause this be?

this is what happens, when i first start the car it shifts fine but after a while it doesn't and smoke starts coming out from the tranny. At first i thought it was just fluid falling on the exhaust, but it's not. As there was nothing dripping. Anyone have any ideas?

Is this in an SVX? The stock SVX rear diff is 3.54:1. Unless the rear diff has been changed, you are burning up your transfer clutch.

Doug

i have a 93 auto impreza tranny in there, the ratio is 4.11

If your sure the front and rear diff are the same ratio, 4.11 then the 93 impreza tranny was no good.:(

Will the Impreza trans work with the SVX TCU?

I think you are the first one to try an automatic with lower ratio dif's. Maybe it's electrical problem with the computer.

oh..i hope that is not true.

You never told us if they installed the rear diff and transmission with front diff from the Legacy or if they just installed thetranny/front diff and left the stock SVX diff in place.

Doug

first off the front diff is in the tranny itself. rite now my car has an impreza tranny with a 4.11 rear diff. Even thought i called Subaru and asked about the ratio, i have a feeling that they are mistaken and it is actually 3.96.

Did the rear diff and tranny come from the same car?

Doug

no, they didn't. The rear diff of the impreza had a smaller housing so i was unable to do it. I had to get a 4.11 out of a legacy to match the tranny.