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MG MGA - transmission lubricant

I will be putting in a rebuilt 4 speed transmission in my 56 MGA. What is the suggested fluid for this transmission? I read that a full synthetic 75W-90 gear oil is recommended. Is this the best option?
N Wessely


You should use the same oil as in the engine, using 75/90 will just make the transmission run very hot and make it uncomfortable in the car because of the heat from the tunnel

Dominic Clancy

Dominic is spot on; use the same oil in the tranny as you do in the engine, typically 10W-40 or 20W-50. Everyone has their own brand that they prefer, with Valvoline VR-1, Castrol or Rotella seeming to be the favorites (I use the VR-1 20W50 as it has a higher zinc content). Here's a link to Barney's site which provides a bit of insight:
Nick Kopernik

Yikes! This scared me. When I joined this BBS years ago everyone was recommending Redline MTL, which I have been using ever since.

I found Barney's article on gearbox oil. Basically he recommends 20w50. But he tried Redline and it wasn't the end of the world.

Tysen McCarthy

Dominic can you explain why the 75/90 generates more heat? Is that because of more viscosity?

I just filled it with MTL and am now thinking of refilling it.
Tysen McCarthy


exactly right.
Dominic Clancy

FYI, 90 weight gear lube is about the same viscosity as 50W motor oil. The have a different viscosity scale. I don't know why it would make the gearbox run any hotter. Reason not to use EP80W90 in the gearbox is because the sulfur additives that give it the "Extreme Pressure" character can damage brass and bronze parts in the gearbox.

I normally use 20W50 oil in my gearbox. I once ran Redline MTL in it for a 12,000 mile test (about a year including hot summer and cold winter). Didn't notice any difference in heat, friction, fuel economy, or any wear problems (or advantages). I really didn't like the way it shifted with Redline in it, and I will never do it again.


This thread was discussed between 20/05/2017 and 25/05/2017

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