hello there my rear diff is whining on my 94 wrx, not sure whats up with it most just be worn, looking at getting a new one, how hard is it change, ive checked the old one and theres oil over it, any suggestions can any mechanin change it, or will it need to be a specialist, also only makes the whinning noise in 1st gear. any help would be great thanks.

 

Normally, I would expect the rear diff to whine in all gears as it is 'linked' to the road speed not gearbox selection.

Assuming it is the diff!:

Simple to get it out, a lot of bolts and the unit is heavy and comes out at an angle due to the two rear mounting studs.
Hard work too as most fasteners are corroded so a good socket set.

Drain the oil first!

Getting the drive shafts out can be a pain.

You can get decent replacement from Welcome to the API website who have rows of them on the shelf sourced from salt-free Japan so all low miles too!

 

The rear diffs often whine due to a lack of preload on the bearings (blame that on the stiff case!) a friend has fixed several whining diffs just be resetting the preload to spec.

Changing a diff is easy, and I remove the shafts using a cold chisel!

Simon