General Tech What oil to use in the gearbox, not rebuilt.

[gbtr6]

Hi,

wondering what hat oil and weight everyone uses for their gearboxes. I think last time I filled it, I used a hypodermic 90 weight. Anyone use synthetic? Is that recommended for an older, non- rebuilt box? I am replacing the seals.

Perry

 

[trrdster2000]

Redline 90. Valvoline makes one for the brass parts in our boxes. Couple of choices.

Wayne

 

[Geo Hahn]

I use a synthetic - Redline MT90. Opinions vary.

 

[gbtr6]

I'd like to use a synthetic, but don't know if that is too 'slick'. Also, being English, it may leak and be an expensive proposition.

Perry

 

[poolboy]

Just use what the book recommends then...A GL-4 90w gear oil if I'm not mistaken.
It doesn't have to be a "hypodermic" oil or a hypoid oil in the tranny although it can be and should be in the differential.

 

[Tybalt]

And that should be a straight up GL4, not one of those listed as GL4/GL5. While there are some that carry a GL5 rating that are safe for the brass bits in our gearboxes, the GL5 are intended for a different usage than in transmissions and interfere with the operations of the syncromesh hubs and rings due to the high pressure load additives for the diff that are associated with GL5.

As for synthetics, I'm partial to either the Redline MT or the Motorcraft Full Synthetic Transmission Fluid (XT-M5-QS) but that is because of some Japanese car exposure, the Motorcraft is popular stuff among the S2000 and Miata crowd.

I have been told not to run the synthetic in boxes fitted with the Laycock overdrives though. One of the old recommendations for OD boxes was to use a non-detergent 30wt, but later that seems to have shifted to a non-detergent 20w-50 (mostly from the BMC crowd and part of a split among the TR and Jag crowds). There are others that say a regular 90 wt GL4 or 85w-90 GL4 (the other side of the split among the TR and Jag crowds) is preferred and even a few that I've heard say use ATF (more among the Volvo crowd, but not much in the way of discussion seen). I've been using Valvoline 20W50 non-detergent racing oil in my TR6 with an A-type OD. If anyone has any experience running either ATF or a synthetic in a Triumph with an OD equipped box, I'd love to hear about their experience.

 

[TR3driver]

I've been running Redline MT-90 (which is a synthetic GL4) in an A-type OD gearbox for over 10 years now (almost as long as Geo has). Works fine. The MT-90 is specifically friction-modified for use in synchronized transmissions; it actually improves synchro operation over conventional GL4. Kind of expensive and not usually found in the corner FLAPS, but the improvement is worth the effort and expense, IMO. Prices vary a lot, so it pays to shop around a little. I eventually bought a case of it on Amazon but their prices change frequently so it may be cheaper somewhere else today.

Oh, BTW, at the risk of being "arrogant" again, I'd like to point out that GL4 is a "hypoid" oil. In the US it's known as "extreme pressure", but that's just another example of two countries separated by a common language.

 

[Tybalt]

I've been running Redline MT-90 (which is a synthetic GL4) in an A-type OD gearbox for over 10 years now (almost as long as Geo has). Works fine. The MT-90 is specifically friction-modified for use in synchronized transmissions; it actually improves synchro operation over conventional GL4. Kind of expensive and not usually found in the corner FLAPS, but the improvement is worth the effort and expense, IMO. Prices vary a lot, so it pays to shop around a little. I eventually bought a case of it on Amazon but their prices change frequently so it may be cheaper somewhere else today.

Oh, BTW, at the risk of being "arrogant" again, I'd like to point out that GL4 is a "hypoid" oil. In the US it's known as "extreme pressure", but that's just another example of two countries separated by a common language.

Interesting about the synthetic use, I had been told that synthetic didn't get along well with the clutch pack on A-Type. I'll keep your using it successfully for ten plus years in mind for future reference.

I agree about both GL4 and GL5 being hypoid or extreme pressure lubricants. The big difference is in the "size" of the extreme pressure additive package, the GL5 carries a much higher additive package loading. At one point there was even a GL6 (still a very few sources, but generally considered obsolete) that was originally developed for the GM front wheel drive Oldsmobile Toronado and Cadillac Eldorado in the sixties.

 

[TR3driver]

Interesting about the synthetic use, I had been told that synthetic didn't get along well with the clutch pack on A-Type. I'll keep your using it successfully for ten plus years in mind for future reference.

In truth, "synthetic" vs "non synthetic" doesn't mean an awful lot, IMO. There was even a legal challenge some years ago that in effect said that anything that has been through a modern refinery (ie hydrocracked) can be considered "synthetic".

So the actual base oil, plus the actual additive package used, is far more important than whether it says "synthetic" on the label or not.

 

[Tybalt]

In truth, "synthetic" vs "non synthetic" doesn't mean an awful lot, IMO. There was even a legal challenge some years ago that in effect said that anything that has been through a modern refinery (ie hydrocracked) can be considered "synthetic".

So the actual base oil, plus the actual additive package used, is far more important than whether it says "synthetic" on the label or not.

Truth be told, that admonition when I heard it goes back to the early days of synthetics when use of PAO base stock for synthetic oils seemed to be much more prevalent than it is now. From what I have seen looking at the Redline information, they are using more of an ester base stock since they hold additive packages better than the polymerized alkenes that form PAO. About the only thing I've been around semi-lately that used really high percentage liquid PAO was in a coolant application, not in any sort of a lubricant application. Bottom line is that it sounds like I can let go of that old "don't use a synthetic in an box equipped with a Laycock OD" belief.