What transmission oil to use

[1340fxd]

I'm going to drain the gearbox & overdrive on my 1976 MGB GT V8 and also the rear axle. What oils are recommended for these please?

[Statler]

I used engine oil in my 1800 gearbox, as recommended.
NAPA 20w50 mineral oil.

The rear diff on the 1800 requires gear oil
NAPA N3031L 80W90 Mineral oil

HTH
Stephen

[Vic Butler]

A Salisbury rear axle is fitted and Hypoid gear oil must be used in them due to the sliding way the crown wheel and pinion mesh
20/50 is ok in the gearbox and overdrive but don't use any additives like Molyslip which will kill the overdrive uni directional clutch.
Changing a leaking pinion seal is a tricky job on a Salisbury axle.Doing it incorrectly will result in a ruined diff. The big advantage is that a Salisbury is much stronger than the normal axle with the ring of bolts on the propshaft side. This type of axle has the pinion engaging with the crown wheel in the 3 o'clock psitio, 90 degrees from the top whereas the Salisbury has the pinion engaging lower down which results in a partial sliding movement hence the need for Hypoid oil. Standard 80/90 is ok for the normal axle.
The Salisbury has the bolts at the rear of the diff housing and needs an axle stretcher to get the diff out.
A few years ago I came across a Land Rover on which the rear propshaft had come off the diff. It was a Salisbury axle and the owner said a mate had replaced the pinion seal. He obviously didn't follow the procedure to the letter as the pinion nut had come undone. It was fortunate it happened at a low speed in town and not at a higher speed. This axle would likely need an expensive rebuild. I haven't seen the owner since.
The MG manual and the Land Rover Series 3 manual give different ways of replacing the seal on a Salisbury but neither are reliable. The later Land Rover Defender manual makes no mention of how to replace the seal on a Salisbury.

[1340fxd]

Thanks Vic. How can I tell if my GT V8 has a Salisbury rear axle please?

[Vic Butler]

There's a metal cover at the rear of the differential held on with bolts. The other type has a ring of bolts on the propshaft side enabling easy removal of the unit unlike the Salisbury which needs an axle stretcher to get the diff out.

[Statler]

A Salisbury rear axle is fitted and Hypoid gear oil must be used in them due to the sliding way the crown wheel and pinion mesh
20/50 is ok in the gearbox and overdrive but don't use any additives like Molyslip which will kill the overdrive uni directional clutch.
Changing a leaking pinion seal is a tricky job on a Salisbury axle.Doing it incorrectly will result in a ruined diff. The big advantage is that a Salisbury is much stronger than the normal axle with the ring of bolts on the propshaft side. This type of axle has the pinion engaging with the crown wheel in the 3 o'clock psitio, 90 degrees from the top whereas the Salisbury has the pinion engaging lower down which results in a partial sliding movement hence the need for Hypoid oil. Standard 80/90 is ok for the normal axle.
The Salisbury has the bolts at the rear of the diff housing and needs an axle stretcher to get the diff out.
A few years ago I came across a Land Rover on which the rear propshaft had come off the diff. It was a Salisbury axle and the owner said a mate had replaced the pinion seal. He obviously didn't follow the procedure to the letter as the pinion nut had come undone. It was fortunate it happened at a low speed in town and not at a higher speed. This axle would likely need an expensive rebuild. I haven't seen the owner since.
The MG manual and the Land Rover Series 3 manual give different ways of replacing the seal on a Salisbury but neither are reliable. The later Land Rover Defender manual makes no mention of how to replace the seal on a Salisbury.

Vic, you've contradicted yourself there, which one is it?
Thanks

[Vic Butler]

No I haven't. I'll rephrase. "The Salisbury axle is much stronger than the normal axle, the latter having the ring of bolts on the propshaft side.'" I thought it was clear but I hope this clarifies it.

[Statler]

Merci, Sir, much better.