Different differential gear ratios front to back?

[danci1973]

I have a '99 Legacy BH 2,5 GX 5MT, which has a 3,700 (open) rear diff. The front diff has the same gear ratio.

There are Subaru LSD diffs with 3,700 ratio, but they seem to be either old and rare (SVX) or rare (a narrow range of 01-02 Impreza RS had those).

I noticed that some Impreza's GT, WRX and STi come with different gear ratios front / back (3,900 / 3,545).

If that works for those cars, would a 3,700 / 3,545 (LSD) combo work on my car (without causing problems)?

If not - why does it work for them?

Thanks, D.

[Hocrest]

SVX's have a 3.54, not a 3.7 (edit, just noticed where you live, you are correct, SVX's are 3.7 in Europe)

The car's that have a mixed front and rear have a 1.1:1 ration in the center differential that allows that to work (3.545 x 1.1 = 3.9)

It is possible to use the LSD carrier from any other Subaru R-160 that you do find with the 3.7 ring and pinion from your car to make your own 3.7 LSD rear.

[danci1973]

SVX's have a 3.54, not a 3.7 (edit, just noticed where you live, you are correct, SVX's are 3.7 in Europe)

The car's that have a mixed front and rear have a 1.1:1 ration in the center differential that allows that to work (3.545 x 1.1 = 3.9)

It is possible to use the LSD carrier from any other Subaru R-160 that you do find with the 3.7 ring and pinion from your car to make your own 3.7 LSD rear.
Thanks.

Now I need to know which are R-160? Or which are not... ;)

D.

[Hocrest]

Almost every Soob mad since the 80's has a R-160 with the exception of some mid 90's Imps. The diffs in those have "thread on sideplates" that look similar to the sideplates on the front differential.

R-160's have sideplates held on with 5 bolts.

Also STI's (in the US at least??) have R-180's, they look similar to the R-160, but they are larger is size to accommodate the larger diameter ring gear (180 mm instead of 160mm)