XJS & XJ from KWE Cars

New technical note: Refilling the GM400 gearbox

In many V12 HE cars (all of which up to 1993 are fitted with the GM400 box) a common issue we’ve encountered, and one that can worry its owners, is for large clouds of white smoke to emanate from the back of the vehicle, particularly on a hot run and after a service.

This is usually a result of the gearbox being overfilled, with the excess being blown out of the breather, which is invisibly placed on top of the box. The oil drips down, hits the hot exhausts and produces an impressive cloud of smoke. Equally, it is easy to under-fill, as the procedure is not widely understood, and dipstick readings can be misleading when oil accumulates in the bottom of the dip tube.

In order to counter such gearbox issues, here is our tried and tested formula:

Speak to the experts

If you’d like expert advice on how to ensure the smooth running of your classic car’s engine, get in touch with KWE Cars. Call us on 01635 30030, like us on Facebook or follow us on Twitter.