5 Speed Gearbox – Centre Differential Replacement

We’ve just had a 1999 WRX RA into the workshop with a failed centre differential unit.

The diff had locked up, making low speed manoeuvering and parking troublesome, causing the car to violently jolt through the transmission whilst steering on a lock.

This is a relatively common issue which seems occur more often with the post 1998 ‘TY754’ five speed boxes, but fairly simple to resolve without removing the gearbox from the car.

A replacement diff unit and gearbox tail gasket were sourced by the customer, for us to complete the job.

After draining the old gearbox oil, removing the exhaust, prop-shaft, gearbox sub-frame and gear linkage, the tail section of the box was removed to expose the drop gears and centre diff unit, which could then easily be removed from the casing.

The gasket surfaces on the gearbox casing and tail housing were then cleaned and degreased, and all of the remnants of old gasket removed prior to re-assembly.

Replacement differential unit and drop gears were installed, new gasket and tail casing refitted.

All the anciliary parts were then refitted, and the gearbox refilled with Millers CRX 75w90 NT gear oil

The car was then road tested to verify that the replacement centre diff was now working correctly.

Problem cured!