the front differential
stock front differential is part of the same casing that contains
the transmission. It also is designed to connect to a motor forward
of it. Since we will not be using the transmission and wish to mount
the motor behind the diff, we needed a replacement. The most obvious
plan is to simply get another stock Subaru rear differential and
mount it backwards.
our motors are designed so that they do not care which way they
rotate, we could drive the new front differential in the opposite
direction of the rear differential to get the wheels to go forward.
The negative of this plan is that the gear cog's faces are designed
to be loaded turning in one direction. Basically, the diff designers,
quite reasonably, did not expect people to drive their car very
hard in reverse.
alternative solution is to turn the differential upside down. When
this is done, the diff can be powered in the normal direction and
still have the wheels move the car forward. The biggest negative
is that mounted upside down, the oil might have problems lubricating.
We are specifically worried about the bearing at the input end of
the differential. Overfilling the diff would alleviate this problem,
but might create excess drag with the gears having to slosh around
the excess oil. A small electric pump with an outlet aimed at the
highest point is another possibility.