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Mechanic recommends 50 weight oil for trans?

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I think the mechanic knows of what he speaks.However, I might ask him what brand of oil he installed and stick with it in the future.---Fwiw---Keoke
 
That's strange. Quantum built me a J-type overdrive and insisted that I use 30wt non detergent motor oil in the tranny/overdrive or the warranty would be voided. What gives with the 50 wt.?

Hi SCGuy, where have you been? Enjoying the Amco bars!

Bill
 
What gives with the 50 weight.? Personal preference I think TR6Bill. I run 60 Weight Valvoline Racing in all my cars no complaints.---Keoke
 
The guru that rebuilt my A type recommended 20w 50 Castrol motor oil. I was surprised that he did'nt recomend a non detergent. He said he's been rebuilding these things forever and the trannys' that have been running the 20w 50 Castrol always look better inside than tranny's using any other lube.

Just what I was told.
 
Hi Larry,

I suggest you go to www.quantumechanics.com and check out the article on gearbox oil with overdrives. John Esposito is one of the most experienced people with the TR g'box & OD units, he's done a lot of testing with different types of oil and I think his advice is pretty trustworthy. You'll find the article at https://www.quantumechanics.com/categories.php?op=newindex&catid=11

Note that John's article is specific to overdrive performance, doesn't really say a lot about gearbox lubrication over the long term, although he seems to feel 30W is adequate. The oil in the combined g'box/OD has to serve both these functions, which might be a little bit at odds with each other in some respects (i.e., lighter oil better for OD hydraulic functions, but not as good for g'box lube, and vice versa).

The answers to your question sort of depends on a couple factors.

If your car has an A-type OD, it runs at significantly higher pressure than the later J-type. An A-type needs 30W or 40W oil. A J-type might use slightly heavier oil okay, particularly if ambient temps are balmy and the car is normally warmed up before driving.

I suspect it also makes some difference if the OD has been recently rebuilt or not. An older unit with some modest wear in it might work best with a slightly heavier oil.

Major considerations are:

<u>Use only non-detergent oils</u> such as "racing" motor oil. This is so it doesn't foam up, which would introduce air into the OD's hydraulic circuit, primarily. Note that many "extended mileage" motor oils are particularly heavy in detergents. Everyday motor oil also has detergent additives to be avoided. Look for non-detergent "racing oil". (Note: Racing oil is non-detergent because the foaming action also can be detrimental to engine lubrication at higher rpms. Because the oil is typically changed very frequently, often after each event, and the engines are rebuilt quite often, detergent qualities are unneccessary. Detergents are used in "street car" motor oils to help remove combustion residues that find inevitably their way into the crankcase. Of course, since there is no combustion, there are no such residues in a gearbox or overdrive.)

<u>Avoid sulphate additives in some oils</u> such as GL5 gear oils, in either non-OD or OD gearboxes (some say the diff too, although I'm not totally certain of this). The reason is that the gearbox contains some bronze or brass parts that will be gradually attacked and corroded by sulphates. A GL4 gear oil contains no sulphates. Suplphates are added to GL5 to better protect high pressure gear contact, but that level of protection isn't needed or desirable in the TR gearbox.

<u>Synthetic oil might cause problems,</u> but there is admittedly some dispute about this. Some folks seem to use them without problems. But, there have been a lot of others who say they began having their gearboxes pop out of gear once switched to synthetic oils. Apparently some synthetic oils are just too slippery for the gearbox design. Switching back to non-synthetic oil seemed to solve the problem. There might be some better formulated synthetics that work well, though. It's also been noted that the overdrive units, which run at high pressure, are more inclined to leak with synthetic oils.

<u>Multi-viscosity oils might cause problems.</u> Again, see John Esposito's testing including multi-viscosity oils, that led to excessively high pressures in A-type ODs, in particular.

Triumph's own gearbox/OD recommendations in '75 TR6 owners manual and Bentley Service manual for all years of TR6 were: 90W hypoid GL4 gear oil for temps above 30F; and 80W hypoid GL4 for temps below 30F. Probably for servicing convenience, the same oil is recommended for use in the diff. (Some earlier service/owners manuals for TR2/3/4 specified different weight and type of oils for gearbox/OD and diff.)

Now, I don't know about your area, but in mine GL4 selection isn't great and what I usually find has a narrow multi-viscosity range: 85W90.

90W or 85W90 viscosity gear oil is close to 40W motor oil, or 20W50 multi-viscosity motor oil. In the long haul, I expect to use 40W "racing oil" in my TR4's gearbox w/A-type OD, but would follow John Esposito's recommendations for 30W "racing oil" during the warranty period with a freshly rebuilt OD unit. 30W might be more useful, too, in areas that see colder Winters than I do here in N. Calif. (Quantum Mechanics is in CT.)

I think the ideal test would be to fill the gearbox with the oil of my choice, hook up a pressure valve to the OD and drive the car around a bit to see how high the hyrdraulic pressure ultimately rises and is maintained in "normal" operation. The problem is that this requires a relatively high pressure gauge that's fitted with an special adapter to be used temporarily in place of the actuator valve cap on the OD unit.
 
At Triumphest in San Diego, some years ago, there was an a forum on the transmissions. The head guy said specifically to use fifty weight racing oil. I belive the brand was Ashland? He has been building/ rebuilding Triumphs transmissions forever. T.T.
 
The Roadster Factory use to recomend 50wt. I have tried different gear oils, synthetic oils, additives, combination of gear and engine oil, molly oil, and the only one that lets my transmission and A-overdrive shift smoother is 50wt (valvoline racing) motor oil. you will notice a difference except mabey in newly rebuilt units.
 
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