Changing the rear-axle (differential) oil on a Triumph Stag

Why, and how often

Renew every few years and top up if low. The Stag's differential is a hypoid unit, the ring and pinion mesh with a sliding action that ordinary gear oil cannot protect. An EP (extreme-pressure) hypoid oil is required.

Steps

1. 01. Warm the car and level it

   Warm the car with a short drive, then chock and raise it so it sits level.

2. 02. Filler plug first, then drain

   Find the filler/level plug FIRST (if it won't undo, don't drain). If a drain plug is fitted, drain fully, clean it, refit with a sound washer.

3. 03. Fill to the level hole

   Fill through the level hole with the correct EP hypoid oil until it just weeps from the hole. Don't overfill, excess can be forced past the output seals.

4. 04. Refit and leak-check

   Refit the plug; check for leaks after a run.