Why to change your final drive ratio

[TomsSVX]

Well folks, I have noticed this for a while now and figured I would share.

1. The early 4eat differential cases were not up to the snuff of the EG33's torque and were notorious for cracking. Subaru beefed up the cases as early as 1993 but mostly 1994+. The heavier cases can be found on every 4.44 transmission you will find.

2. The 3.545 gears are great for highway traveling, but suck for one reason. To get the 3.545 ratio they are required to have 11 teeth on the pinion gear. Now while they maintain the same gear diameter as the other ratios this means there is less material per tooth, which translates into less strength to handle significant torque and esp being shock torqued by hard shifts or sudden forward to reverse changes. The 4.44 gear ratio differentials have 9 pinion teeth which significantly increases material per tooth and essentially makes them stronger which is why we do not see 4.44 differential failures as common as the 3.545.

3. X-contamination of fluids is also a common cause of differential failure. There are two seals that seal the diff fluid from the AT fluid and visa versa. These seals can and will fail, thus contaminating the differential with a lighter weight oil and overfilling it. This will cause premature pinion shaft bearing failures which will not only be noisy but can cause rapid gear wear and eventual total failure. While this may not be a reason to change ratios they should be replaced EVERY time you change a differential in the transmission.

Just a little info for those looking for a good reason

TOm