Manual Transmission Lube (MTL)

[acampbell]

During an episode of Jay Leno's Garage Jay mentioned that they only use MTL in their manual transmissions. I have read glowing reports on several blogs about this lubricant. What are your thoughts and/or experiences in using this in our TABC?
The version I found here in the U.S. is produced by Redline and it is labeled as "MT-90, Full Synthetic Gear Oil, High Performance Lubricant for Manual Transmissions and Transaxles". Any thoughts or comments?

[Duncan M]

Redline makes great oils, but you do not want to use 90 weight in a transmission that calls for 140 weight. If you try 90 weight in the stock TC transmission it will make unwise sounds while cruising in 4th gear.

[Steve Simmons]

Some people use it and like it, but the lubricant Redline recommends for our gearboxes, and the one I use in mine, is 75W-140NS.
https://www.redlineoil.com/75w140-ns-gl-5-gear-oil

[Bob Schapel]

Someone should do a thorough study on gearbox oils for our T-Types. I don't know enough to draw conclusions, but here is a bit of info' I have gleaned.
Many years ago, I was given two one-gallon tins of very old (but unused) Mobil 140 gear oil. I had been using a more modern (1990s?) 140 gear oil in my road-going TC gearbox. I was under the impression that all was OK with the "modern" oil ...... BUT ...... when I drained the "modern" oil and re-filled with the old c1960s Mobil oil. I was immediately amazed with the 100% improvement in the synchromesh!
Oil lubricates the gears, but the synchromesh works on friction (or is it viscous drag?)
Friction modified oils are good for transmitting power and protecting against wear. BUT synchromesh works on the friction/drag in the synchro' rings.
Do we have to choose between good sychro' and good friction/wear reduction? It would be great to have both but my guess is that we have to choose?
My road-going TC is overdue for an oil change. What should I use?
Bob Schapel

[Duncan M]

Bob-
Note that my comment above about "unwise noise while cruising in 4th" with 90W oil has nothing to do with synchromesh function.

I have tried several brands of multi weight 140's, plain old GL4 140W, and the MTL (90W) that clearly is inappropriate. The synchro's worked quite well with each type. I have settled on the same oil as Steve, the Redline 75W140 NS. And if anyone is wondering, all Redline gear oils are yellow metal safe, even though they carry a GL5 EP rating.

[Steve Simmons]

Interesting observation, Bob. I'd guess that the old oil wasn't very slippery, so the syncros worked better. The downside of that of course is wear. The Reline NS oils have reduced friction modifiers to help synrcos work better. Wear reduction is still good thanks to modern oil technology. It should be superior in every way to the old stuff.

[Bob Schapel]

Thanks Steve and Duncan. I should try the 75W140 Redline. I will investigate its availability in Australia. Or maybe there is an oil here which is equivalent?
I have heard differing explanations regarding synchro'. Do you know if it is friction or viscous drag, upon which our T-Type synchromesh boxes rely? A bit academic really, but I like to know how things work.
I do use 90 grade oil in my race TC. However, that is a car where noise is not an issue.
Bob Schapel