Gearbox Oil in 1959 Dominator

Mick Hemmings says EP90, good enough for me! 

I have used 40, EP 90, and ATF, no issues with any of them. I liked ATF as its easy to spot leaks (red) and the thinner lube must release a little power with lower churning losses, it also must find its way into the bushes in the sleeve gear easier than thicker oil . Its a very sturdy box ,lube type not critical , just fit a breather to inhibit rust.

They only recommended the oils available at the time, BSA recommended the same oils in the 50's and by end 60's they had changed to EP90 which was developed in the mid 60's, which has the same viscosity as a straight 50W engine oil. Haynes followed the same path using Castrol recommended oils as they had a tie up.

I've read that some modern transmission oils are mean to yellow metal. In my TTI gearbox, TTI recommends Motul Gear 300 Oil 75W90 GL-5. The data sheet for that oil says it don't harm yellow metal. So I use it in AMC boxes too.

Hello all well if you read you, Norton Manuel, right you can see that is says  Wakefield Castrol  w40 Or  ST90  Or Duckham SL4 80-90w    Never use EP90 oil as this dissolves bronze in time also See WWW Lucas oils Com                                                                                               yours Anna J

The original EP oils contained sulphur based additives which attacked bronze bushes but they have nearly all been reformulated, regardless the Glacier Bearing Engineers manual tells you the effect only happens above 100C.

 After about 30K miles my gearbox bush set were all worn  enough to need replacement, Sleeve gear bushes were the worst.  I decided that the oil was not getting thrown around enough and did not have an easy path to the bushes. To this end I went for the thinnest EP oil I could get. I have since tried ,ATF and  30 monograde with a moly additive. Not had any problems with wear ,but rust has been an issue ,A vent is essential in my opinion. And regular oil changes in damp climates. Back in the 1970's I noticed that car Box oils  were being switched from EP90 to ATF with no changes to the box design, all for better fuel economy. Seemed a good idea. Modern box oils are now a very different thing to the old EP oil.