Which oil for LH overdrive gearbox?

larrylamb11 · Post by **larrylamb11** » Wed Nov 14, 2018 1:50 pm

I'm quite surprised not to have found a definitive answer to this having searched both here and the interwebz via Google....

Original Reliant specification for the gearbox with overdrive is EP80, correct? Yet it seems most other Laycock overdrive 'boxes use engine oil, straight 30 or 20w/50 or similar... as is specified for the MG gearbox (with the same LH overdrive unit as the Scimitar) as I understand it.

I know if gear oil is being used it must be GL4 and not GL5 for the additives and I think I am right in saying that actual viscosity is very similar between 80 weight gear oil and 20 weight motor oil, so the 'thickness' of the oil is very similar between the two camps, but is there a definitive recommendation that has distilled over the years for the Scimitar?

What are other overdrive owners using in their gearbox?

Post by **philhoward** » Wed Nov 14, 2018 2:05 pm

I think that the internal pressures might be different in the overdrive between an MGB and a Scimitar (I was trying to find this out for another reason) but the oil requirement is set by the gearbox, not the overdrive and the Ford gearbox uses EP80, so that’s what the overdrive uses. I’m not sure 20/50 would be suitable for the gearbox..

Post by **Roger Pennington** » Wed Nov 14, 2018 2:29 pm

Certainly I've always used EP80 as that's what it says in the official workshop manual, which is the definitive answer as far as I'm concerned

Post by **scimjim** » Wed Nov 14, 2018 3:14 pm

discussed previously here (archived in members only area).

it stems apparently from the MG community's concerns of the sulphur content of EP oils eating parts of the gearbox ( not the overdrive)

larrylamb11 · Post by **larrylamb11** » Wed Nov 14, 2018 4:14 pm

EP80 it is then. Thanks for the clarification

Post by **Nigel Clark** » Wed Nov 14, 2018 4:45 pm

It needs to be EP80 GL4. Don't use the commonly available GL5 version as the additives can attack brass and bronze components due to high sulphur content.

Nigel

Post by **Roger Pennington** » Wed Nov 14, 2018 6:27 pm

Yes I'd agree, I've always used GL4 as I understood GL5 was bad for "yellow metal" parts as Nigel says.

Post by **Dennis Nicholas** » Thu Nov 15, 2018 6:13 pm

GL4 75W/90 box/gear oil. is an alternative....used to be available at very good discount price from the late Alan Dean's brother's oil company to club members (Contract for supplying a certain retailer restricted him from selling to any other source....including Scim club).
And of course use AFMT (Anti Friction Metal Treatment) from Synionic via the discount deal I have arranged for the club. (lab test results available).

Dennis