Triumph Spitfire, GT6, TR4A, 250, 6
To prevent final drive/differential housing pressurization and subsequent pinion and inner axle shaft oil seal/gasket leaks, it is recommended that the breather hole in the differential housing be cleared of any debris or dirt likely to cause a breathing restriction.
The axle/differential-housing breather for the above models is located adjacent to the right hand rear housing/ chassis mount. Ease of access varies with the model. Some models will have a split pin through the breather hole, others a solid pin. (The purpose of this pin is to “jiggle” during vehicle motion and so keep the hole clear). The location encourages large amounts of silt to build up and will completely bury the breather.
Whenever the rear axle oil is checked ensure that the breather area is completely clear of any dirt/silt build up and ensure the pin is free in the breather hole.