The rear axle is one of the T-Series' more durable components, but it is not maintenance-free — and when it does complain, it usually does so in one of three ways: an oil leak onto the brakes, a whine on the move, or the slow onset of bearing wear. Here is how the axle is put together, the oil it wants (which is not the same as the gearbox), and how to read its symptoms.
How it is built
The T-Series drives through a live rear axle with a hypoid final drive — the crown wheel and pinion set that turns the drive through ninety degrees and provides the final gearing — feeding semi-floating half-shafts out to each rear wheel. The final-drive ratio is around 5:1, though it varies by model and market, so check your own car's figure. It is a simple, sturdy design that will cover big mileages if the oil is kept up and clean.
The oil it wants
This is the single most important thing to get right, and the easiest to get wrong: the hypoid rear axle requires a hypoid (EP) gear oil, typically an EP90, because hypoid gears need the extreme-pressure additives to survive. Do not confuse it with the gearbox, which on these cars is often specified with a different, non-EP oil to protect its yellow-metal bushes and synchromesh. Fill the axle to the level plug with the correct hypoid oil and check it as part of your regular under-car routine. (Confirm the exact grade for your model against the handbook.)
Leaks onto the brakes
The commonest complaint. Oil weeping past the pinion seal at the front of the axle, or — more seriously — past the hub and half-shaft seals at the ends, can find its way onto the rear brake shoes, glazing them and causing grabbing, judder or a pull. If you find oil on a backplate or a contaminated shoe, do not just clean it: cure the leaking seal, or it will return. Overfilling the axle, or a blocked axle breather, can also force oil out past the seals, so check those first.
Whine and wear
A steady whine that rises and falls with road speed (not engine speed) usually comes from the final drive — worn or incorrectly set crown wheel and pinion, or worn pinion and carrier bearings. A whine only on the overrun, or only under drive, points to backlash and mesh that are out of adjustment. Setting up a hypoid crown wheel and pinion — pinion depth, bearing preload and backlash — is specialist work and not a job to rush; if the axle is merely a little noisy and the oil is clean, many owners simply keep it fed and live with it. A clonk on taking up drive, by contrast, is more often worn half-shaft splines, universal joints or a loose propshaft than the differential itself.
Keeping it healthy
Keep the correct hypoid oil topped to the level plug, keep the breather clear, cure any seal leak promptly before it reaches the brakes, and listen for changes. Treated this way the T-Series axle is one of the car's longest-lived assemblies. Always confirm oil grades, the final-drive ratio and any settings against your car's own handbook.
*Written for the T-Series Archive. Oil grades, ratios and clearances vary by model — confirm them against your own handbook.*