Gearbox oil

ChrisD200 · Post by **ChrisD200** » Wed Mar 26, 2008 5:18 am

Hi guys. Many thanks to all help given with the last request on electrics. I wish to change the gearbox oil on my 1951 G9 (CP box). The instruction manual states SAE50 for summer. But I cannot find any SAE50 here. By UK standards it is nearly always summer here in South Africa so I don't want to use too thin an oil so I suspect a 20-50 will be too thin at starting (maybe all the joints will leak). So should I use an SAE40 instead of the recommended SAE50 or should I go for the lowest viscosity EP type oil?
Secondly, once the gearbox is properly filled (1 pint) should I be able to see the oil level looking through the filler cap?

TommoT · Post by **TommoT** » Wed Mar 26, 2008 6:03 am

You can use any dedicated gearoil, like SAE80/90, available most places. The SAE80/90 designation was invented avoid confusion with ordinary engine oil, but it has the same viscosity as SAE40/50 engine oil. And don't listen to old urban myths telling you that modern EP (Extreme Pressure) gearoils will eat your bronze bushings. Oil companies claim this to be a thing of the past, and on a personal note I have been using these oils in my Burman (B52) box for years without any ill effects.

GSAX1 · Post by **GSAX1** » Wed Mar 26, 2008 7:29 am

Hi Chris.

You can use straight SAE90 gear oil, as the viscosity is quite similar to SAE50 motor oil. I use SAE 90 in my BMW boxer gearbox, as this keeps the rattling down to an acceptable level. 80W90 is somewhat thinner and makes the box noticeably louder when hot. I have found SAE 90 in GL1 (non-EP) also. That would be a better choice than GL5 (Hypoid/EP) since you don't need the additives.

Michael