Transmission Gear Oil - Synthetic?

[dklawson]

I'm sure this has been covered before so please be excuse the repeated topic.

I know I'm not supposed to use GL5 lubricants in the TR gearbox. ALL the organic (non-synthetic) gear oils in my local parts stores are GL5 rated. They do have a synthetic that is GL3, GL4, GL5 compatible. My question is... does the GL5 gear oil warning apply to synthetics or just the organic oils?

I can certainly order a quart or two of Red Line or Amsoil GL4 lubes. I'd just like to know if it's necessary or if I can use the multi-rated synthetic instead.

Thanks in advance for your suggestions.

 

[RobT]

Is it an overdrive box?

I have a OD box in the TR and I followed the conventional wisdom which seems to be use 20W non-detergent motor oil (what Quantum Mechanics recommends).

In the Lotus I use Redline MTL which is a GL4 synthetic, and I noticed a distinct improvement in the shifting (not sure what was there before though).

Rob.

 

[TR3driver]

Doug, we've debated this topic endlessly. My opinion is that the GL5 warning does not apply to even all conventional oils, and virtually no synthetic gear oils.

The real problem is that the GL5 gear oil specification is not restrictive enough, and <span style="font-weight: bold">can </span>be met using a cheaper additive that breaks down and attacks 'yellow metal'. But not all makers use the cheap additive. The difference becomes apparent when you drain the oil, as the broken-down additive is also what gives used gear oil that distinctive smell. The Valvoline full synthetic GL5 gear oil that I use in all my Triumph differentials never smells like that, giving me confidence that it does not use the sulfur-based additive that breaks down to form sulfuric acid (and attack yellow metal).

Also, the "west coast" "conventional wisdom" is to use Valvoline 20W50 Racing motor oil in TR overdrives, as it has an "anti-wear" additive that helps protect the countershaft thrust washers; and the multi-viscosity characteristic also helps shifting when very cold and very hot. Ken Gillanders did some extensive tests with it in his personal TR2 (dubbed the "Red Rocket", winner of several drag racing trophys) that showed it to be superior to non-detergent motor oil (which also lacks anti-wear and multi-viscosity additives).

 

[dklawson]

Thanks Randall. I was certain the topic must have been covered before but my search yielded threads covering everything but. Based on Rob's and your comments I'm now comfortable using the GL5 synthetics... but I've also heard others recommend Red Line MTL.

This is still for the project Spitfire. The gearbox is a later (non-overdrive) single-rail being transplanted to replace the car's original 3-rail box. I'm still collecting the parts I need for the swap so I may opt for the Red Line even if I have to mail order it.

Thanks again.

 

[TR3driver]

so I may opt for the Red Line even if I have to mail order it.

FWIW, I bought mine through eBay, far cheaper than I could find it at local stores or the usual on-line shops. Kept looking until I found some that was local enough I could pick it up in person and avoid shipping charges.
YMMV

 

[dklawson]

Thanks again Randall. The eBay sources I found for the gear lube wanted as much to ship the oil as they were charging for it by the quart. I found a (more-or-less) local Red Line distributor who has stock of the MT-90 lube for $10.50/quart. They also have Saturday hours so I guess I'll make a road trip this weekend.

 

[SpannerMan]

My experience with the red line MT90 has been that it does make shifting in cold temperatures better, but if you have any leaks it will leak out faster. It is pretty runny stuff.

 

[dklawson]

Thanks for that. The gearbox is new to me so I don't know how much leakage to expect. However, I did fit a new gasket between the bell housing and the gearbox and I fit new seals for the output flange and speedo drive. If the tailpiece gasket doesn't leak I should be OK. But... I'll keep an eye open for leaks.