TR4/4A What kind of oil in overdrive gearbox?

[shoopal]

I found my overdrive problem thanks to Leo Ruof and John from Quantum Mechanics. Stuck cone clutch.
Now I am ordering the gaskets and seals to put it back together and I'm totally confused as to what kind of oil to use.
Leo (veteran of 300+ OD rebuilds) is adamant for SAE 20-30 as is the Laycock shop manual (PUBLICATION PART No. 502274). On the other hand the owners manual (p 16) and other sources are recommending GL4 80-90 wt gear oil.
What say you all?

 

[Merlin63Tr4]

Opinions/recommendations are all over the place as far as what is the “correct” oil for the overdrive gearboxes.

The TR4 owner’s manual says 90 weight GL4 gear oil.
Rebuilders call for everything from straight SAE 50 motor oil to SAE 10W-40, 20W-50 motor oil and so on.
If I remember correctly my brother's old MGB used SAE 30 motor oil.
My Volvo uses ATF (275K miles on that one).

On my TR4 I originally was using 80W-90 GL4 gear oil, I’m currently using Redline MT 90 GL4 gear oil.


M.

 

[TR3driver]

This topic has been endlessly debated, with no clear winners. The legend, as I heard it, is that Standard-Triumph changed their recommendation (to GL4) based on having too many warranty gearbox failures. The early TR2-3 owners manuals do specify either 30 weight or 50 weight motor oil (depending on outside temperature) but changed around 1958-60 to specifying GL4 gear oil (80 or 90 depending on outside temperature). Supposedly the extreme pressure additives help protect the layshaft bearings and thrust washers (which are a known weak spot in the TR2-6 gearbox).

Personally, I couldn't see any change in OD operation when I switched from running Valvoline VR1 20W50 to Redline MT-90 (which is a 75W90 GL4 gear oil). But it sure made a noticeable difference in how well the main gearbox shifted.

Worth noting, perhaps, that the oil "grades" (eg 30 weight or 90 weight) are deliberately different between gear oil and motor oil. It's tempting to think that 90 weight is 3 times as thick as 30 weight. But the MT-90 is roughly the same viscosity (at the same temperature) as 10W40 motor oil!

 

[TomMull]

Worth noting, perhaps, that the oil "grades" (eg 30 weight or 90 weight) are deliberately different between gear oil and motor oil. It's tempting to think that 90 weight is 3 times as thick as 30 weight. But the MT-90 is roughly the same viscosity (at the same temperature) as 10W40 motor oil!

You are right to point out this common misconception and your example does get the point across and probably needs no further comment. However, at the risk of muddling the point, it might be better to say that the weights would be very similar at operating temperature (high) since the 10W40 would be much less viscous when cold. This could be significant if we assume that many gearboxes run at a lower temperature than engines. Might be even better to compare multi viscosity gear oils with multi viscosity engine oils e.g. 75W90 roughly equivalent with 10W40.
Tom

 

[TR3driver]

You are right to point out this common misconception and your example does get the point across and probably needs no further comment. However, at the risk of muddling the point, it might be better to say that the weights would be very similar at operating temperature (high) since the 10W40 would be much less viscous when cold. This could be significant if we assume that many gearboxes run at a lower temperature than engines. Might be even better to compare multi viscosity gear oils with multi viscosity engine oils e.g. 75W90 roughly equivalent with 10W40.
Tom

Sorry I wasn't more specific, Tom. Redline MT-90 is, in fact, a 75W90 gear oil. Pretty much all synthetic oils wind up being "multi-weight" as they don't change viscosity as much over temperature as the "dinosaur juice" does.
https://www.redlineoil.com/product.aspx?pid=46

You are quite right, a straight 90 weight oil would be much thicker at lower temperatures, more comparable to a straight 40 (or 50) weight motor oil.

 

[tdskip]

Non-detergent 30 weight is a safe choice.