Best J type overdrive gear oil

[markythesparky]

what is the best oil for a spitfire 1500 gearbox with overdrive oil reading a few articles all seem to have different ideas re GL-4 or GL-5.

[Clive]

Never seen anybody suggest GL5 in a proper article. GL5, unless specifically yellow-metal safe will be bad for the synchro rings etc in the gearbox. 

Stick to a GL4, the factory spec. Now, EP80, EP90, EP80/90 or possibly EP75/90, all available as GL4.

[sparky_spit]

Generally, if you use a GL4 spec oil in your overdrive/gearbox you can then use it as well in your differential and saves buying two different types.

GL4 spec gives you protection against unwanted oil attack on yellow metals, which you will definitely have in your diff, and may possibly have in your gearbox.

Also, you need an EP type oil (Extreme Pressure) for use with hypoid type gears.

So, look for an oil that is the right viscosity (80 to 90 weight) and is EP rated and is GL4 compliant.

80w/90w EP GL4 gear oil is available from Halfords, Comma, Castrol and others.

Or you can go upmarket and get top quality competition oils such Millers Synthetic CRS Nanodrive in various grades from 75w - 90w up 75w - 140w, but these are more specific to gearbox or diff (standard and limited slip) and not all can be used in both.

70

[thescrapman]

Some people use 20/50 engine oil in the Triumph gearboxes.

Despite not seeing them have any issues I have not been brave enough to try yet.

Other manufacturers did spec 20/50 such as MG for the B box.

[RobPearce]

Technically, a gearbox doesn't have the sliding contact of a diff pinion that forces the use of EP spec oil, so using ordinary 20/50 is probably OK. On TR7s with the SD1 box, the factory even specified ATF for a while! The point is, the EP additives do reduce the wear on the (slightly sliding) slant-cut gears, so the same gearbox can be rated for higher torque if EP oil is used. I would certainly want to stick with EP90 on a GT6 but the 20/50 is probably fine for a 2000 saloon.

[WIMPUS]

I've always been using Millers 80w90 GL4 on my Spitfire with J-type OD.

Been happy about it.