TR6 API GL4/GL5, Recommendations from Valvoline

[Bob_TR6]

FYI:

Just contacted Valvoline as to their recommendation for transmission/differential oil for our Triumphs.

My email to them:

Hi Valvoline: I'm looking for a suitable lubricant for a 1973 Triumph TR6 differential+Manual transmission. The shop manual calls for: "BP Gear Oil SAE 90EP" -OR- "Castrol Hypoy" -OR- "Duckhams Hypoid 90" -OR- "Esso Gear Oil GX 90" -OR- "Mobilube HD 90" -OR- "Petro-Fina PONTONIC MP SAE 90" -OR- "Shell Spriax 90EP" -OR- "Texaco Multigear Lubricant EP 90" =>>All of which are spec'd to be API GL4. As you know, most oils nowadays (and all the oils on the shelf at my local shop) are GL5--although some are GL5/GL4. The problem, I've been told, is that GL5 isn't good for yellow metals.
Which of your products do you recommend for this application?

Their response:

To meet API GL-4 standards, we produce the Valvoline Synchromesh Fluid (part number 811095). The Synchromesh product is 100% safe and compatible to metals used in GL-4 applications.


Anyone have any comments before I go buy a couple pints?

 

[Andrew Mace]

Only that I've been very happy with Redline's MT-90 75W90 GL-4 Gear Oil, which has been great in my Herald's gearbox: https://www.redlineoil.com/product.aspx?pid=46

 

[dklawson]

We have also used the RedLine MT-90 over the past few years in our Triumphs. We have not experienced any problems.

 

[TR3driver]

Valvoline's full synthetic GL5 gear oil works just fine in TR differentials. It contains none of the additive that can attack "yellow metal". I've been using it for over 30 years and credit it for making the diff in my (previous) TR3A last so long. It was already well worn when it came to me in 1983; but still working fine when the car got wrecked in 2005, roughly 200,000 miles later.

However, it is too slick to work well in a synchronized transmission. Their synchromesh oil will probably work fine; but I also use Redline MT-90 in my Triumph gearboxes (both A and J type).

I wouldn't use either of them in the diff, though. Synchros require friction to operate, but you want as little friction in the differential as possible.