TR4/4A Diff Fluid - GL4

I was looking for GL4 diff fluid and a local Diesel shop sells AmsOIL so I took a look.

Here is what I found. AMSOIL Manual Transmission & Transaxle Gear lube SAW 75w-90 APi GL-4

I think that should work... it is synthetic but also Gl4.

Since it does not mention differentials I would proceed with caution.

Redline MT90 specifically says 'not for use in hypoid differentials' and I see no such prohibition on this bottle but still I have doubts.

If nothing else, it makes no sense to me to use an oil that is optimized for friction (ie synchro rings); in an application where friction is the enemy (like a hypoid differential).

FWIW, I've been using Valvoline Synpower (GL5) in all my differentials for many years (over 20 years in my previous TR3A, current TR3 hasn't been on the road that long since I got it). The 3A diff was already well worn when it came to me (with over 150,000 miles on it), and I credit the Synpower for making it last while I put another roughly 200,000 miles on it. Was still working fine (in spite of all the backlash) when the car was wrecked.

In spite of the GL5 rating, the Synpower has none of the additive that attacks "yellow metal". It doesn't even have that distinctive "old gear oil" smell when I change it (the smell being some sort of hydrogen sulfide compound related to the sulfuric acid that attacks yellow metal).

+1 on the Valvoline Synpower.

jim

You really don't need the GL4 in a differential anyway, as there is no yellow metal. Get a quart of the Valvoline; it's cheap and available.

Sarastro said:

You really don't need the GL4 in a differential anyway, as there is no yellow metal.

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Actually, there is, in a TR diff. Here's a shot from my Stag diff (the TR2-6 diff uses the same piece).


Note how dark the edges and thrust surfaces are. I believe that is a result of using oil containing sulfur. The washers weren't ruined, but were well worn and the main cause of excessive backlash. The thrusts for the side gears (which are not brass, see similar pressure and should have more movement) were much less worn.

So yes on use in the tranny but not the diff??

Zitch said:

So yes on use in the tranny but not the diff??

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Should be OK, but I have no personal experience with it. I like the MT-90 so much that I ordered a case of it (through Amazon IIRC) and haven't used it all yet