MG T-ABC

Just finished rebuild on my 48 TC 5315. Out racking up the miles before first oil change and valve adjustment. I plan on driving the car a lot. The only issue I am having is after driving the car for two hours the transmission starts to grind gears. I have trouble getting in to first at stops and down shifts are more difficult with out grinding. It seems to be temperature related as the oil in the transmission heats up. Have any of you had the same issue and how did you solve it. What oil weight for the transmission is the best to hard driving? Currently using SYN GEA OIL 75W 140. Thank you for your help.

Like so many things in life, opinions will differ...

I use Redline MT90 inb my TC transmission, and find it helps shifting considerably. Whatever you use, make sure it is GL-4 and not GL-5. The latter will damage the brass parts in the transmission.

Tom Lange
MGT Repair

I used Sta-Lube EP140W for many years, and a couple years ago switched to Redline 75W-140NS. Neither fluid gave me any issues whatsoever and performed similarly. The latter is considered by many to be the best fluid for TC gearboxes. Some use the MT-90 like Tom but it's thinner. Redline actually recommends the 75-140NS over the MT-90. If you go this route, be sure to specify "NS", which has a modified anti-slip package to help the syncros work better.

When it comes to yellow metal friendly oils, Tom is correct in that GL4 oils are less corrosive when they get worn out/acidic, because they start out with less sulfur compounds as EP additive. The Redline 75W140NS oil Steve suggests is GL5 and stinks of sulfur, but it also has listed on the label a military specification called "MIL-PRF-2105E." That Mil-spec requires a very good performance on an ASTM copper corrosion test-- D130. To meet GL4 spec, a gear oil must also test very good on the D130 test.

I have been using the redline 75W140NS, and compared to other oils I have tried--it is nothing special. If the oil does not list the MIL-PRF-2105E on the label, then you want one labelled GL4, or GL5 AND GL4 to ensure genuine yellow metal friendly.

Has the OP tried adjusting the clutch? Maybe it is not fully engaging when the pedal is pressed down.

There are yellow-metal-safe GL-5 oils, but they have to be labelled as such. I believe all Redline oils are safe for yellow metals.

It's odd that they say it can be "mixed with 75W90NS or MT-90 to bring viscosity level up". I wonder if that's a typo, considering MT-90 is a thinner oil at 75W-90.

https://www.redlineoil.com/75w140-ns-gl-5-gear-oil

Do not trust a label just because it says "yellow metal friendly." Most any oil is safe for yellow metals as long as it is fresh. If it is not labelled as having passed GL4 or MIL-PRF-2105E it simply is not yellow metal friendly in the long term.

Royal Purple, for instance, has a line of GL5 gear oils they claim on the label is safe for yellow metals, yet they perform horribly on the D-130 test.

I tend to trust Redline. Their whole purpose to exist is to serve classic and performance cars. They wouldn't survive if the products were shown to do damage in those cars.

Just because it came up, I've had Royal Purple in the rear ends of all my old cars for decades with no issues. My MGB GT has run it since around 1980. The copper thrust washers have been replaced three times I think, which isn't much for an MGB over so many miles. But I'm not a chemist so I can't comment on acceptable limits of corrosion. I do change my rear end oil at the recommended factory intervals, which is probably far more often than modern gear oils require to be changed.

I wonder how "not safe for yellow metal" oils would test in comparison. If a lot different, then I wouldn't worry about the ones that are.

I think you just answered your own question on Royal Purple. Lucas Oil is another one that tests badly on the D-130 test and would never pass the Mil-spec or GL4 standard (which both require a very good rating from the D-130 test). As I stated early on, the label on the Redline 75W140NS states it HAS passed the Mil-spec which indicates it is in fact "yellow metal safe." No need to be a chemist or oil testing engineer to make an informed decision. The testing procedures are all in place for that.

I have been in and out of old British gearboxes for years and years and who knows what sort of gear lube has been put in them by the umpteen people that have owned or serviced these cars. I have never seen a yellow metal synchro ring or thrust washer that I could tell was damaged by the wrong gear oil. Plenty damaged by abuse or just plain wear and tear and neglect. Please tell me what damage caused by the wrong gear oil looks like???

I use Lubriplate lubricants exclusively. No connection or investments, just exceedingly high standard products. I use SPO 277 in the gearbox.

https://www.lubriplate.com

Brian

I found the straight weight 140's foamed like crazy in the TC transmission. SO much that you could not even check the level.
I think I will drain the Redline NS and try the MT90 as Tom suggests.

Royal purple, Redline, and Lucas are all newer products, which is fine. But, as I used to work around alot of heavly used machinery, like in steel mills and glasshouses and heavy construction, I recommend the Lubriplate products. Your opinion may vary, and obviously does. Oils and lubes are a highly controversial subject for some reason which I do not understand. Probably just what you think is best, I guess.

Guys thank you or all the information. Sorry it has taken me so long to get back to you all, but I have been out of touch. you have given me much to think about.

I drained the 75W140NS redline after the last TC drive and replaced it with MT90. Straight. Went for a lengthy drive in 80 plus degree temps yesterday and I can report a distinct improvement. Thanks for the good tip, Tom. Maybe it is true about all that sulfur not agreeing with synchro's?

Duncan thank you for your in put.

Lasloja-
I have taken another drive with the Redline 90W and completely changed my mind about it. Oil film thickness on gear teeth is simply not up to the task. While it shifts fine no matter what oil is in there, a problem becomes obvious when the oil is warm and we are motoring along. Gears are not meshing properly from the lack of film thickness, and it creates a sort of noise that will only occur with an oil that is too thin. I have switched to a different multiweight 85W140 that is very low in sulfur and rated GL4/5

Thank you Duncan, i have not had time to do anything yet.

Interesting observation, Duncan. I've heard several people say they didn't like MT-90 but I don't recall ever hearing why. This viscosity issue may also be why Redline recommends the 75W-140NS for TC.

Steve what are you using?

I've been using the aforementioned Redline 75W-140NS for a couple years now. No complaints so far. I'm not sure how many miles I have on it, probably a few thousand.

Link: https://www.redlineoil.com/75w140-ns-gl-5-gear-oil