View Full Version : TR6 TR6 gearbox fluid?

04-16-2012, 05:16 AM
So...what is the recommended gearbox fluid-TR6-'74' by this forum??

04-16-2012, 05:41 AM
Here is what has been suggested but not limited to
30 weight non det motor oil
80 90 weight gear oil extreme pressure EP
ATF fluid

I use GM synthetic Manual transmission fluid that goes in the late model corvette


04-16-2012, 06:56 AM
Many use Redline MT90 especially in OD transmissions.

04-16-2012, 09:26 AM
I use 30W ND motor oil as recommended by John Esposito at Quantum, mainly because I have a "J" type overdrive. As stated, others like different oils, but for me this works just fine.

04-16-2012, 09:49 AM
Many use Redline MT90 especially in OD transmissions.

But I like it mostly because it makes the gearbox shift so nice. OD operation wasn't significantly better than with VR1 20W50.

Note that Triumph specifically recommended GL4 "gear oil" from about 1960 onward through the end of the TR6. The "extreme pressure" additives help protect the thrust washers on the countershaft. Even John Esposito notes that they are a weak spot in this design, and advocates replacing them with Torrington bearings. The MT 90 is a lot cheaper than the modification.

PS, MT-90 is rated GL-4 (meaning it provides at least that much protection). But it is also optimized for use in manual transmissions and contains none of the sulfur-based additive that can corrode brass components. (Said additive is found in most conventional GL4 and GL5 gear oils.)

04-16-2012, 10:10 AM
You can still get this thru if not in NAPA stores. Pretty close to the 40+ year old factory recommendations for gearbox and differential.

04-16-2012, 10:47 AM
Is the MT90 a synthetic lubricant?

04-16-2012, 10:59 AM
"Redline MT-90"

04-16-2012, 11:22 AM
Is the MT90 a synthetic lubricant?

Yup. Also kind of pricy even compared to more common synthetics. Prices vary, so it's worth shopping around a bit. I found a partial case on eBay for about $11/qt.

04-16-2012, 12:33 PM
Are there other synthetics you can buy locally that are equal to Redline? And work with OD..?

04-16-2012, 12:57 PM
My local "performance" auto parts store has MT-90 on the shelf, but last time I asked, they wanted something like $18/qt for it.

I'm not aware of anything else that is equivalent and more readily available. Although I've heard good things about GM "synchromesh fluid" in other manual transmissions, it is quite a bit lower viscosity, which may or may not present an issue in a non-OD TR gearbox. Since all my Triumphs have overdrive, I've not been tempted to experiment.

Here's a nice white paper on the subject, which suggests Amsoil MTG as being equivalent to the MT-90. But I think you're even less likely to find Amsoil on a local shelf than Redline.

04-16-2012, 01:17 PM
I'm using Brad Penn's 89w90GL-4. Pretty new product but so far seems to work pretty well.

04-16-2012, 02:45 PM
Wow. When I bought my MT90 it was $8.00 a qt. The Stalube was $13.00 a gallon.

04-16-2012, 05:23 PM
My rebuilt OD tranny was originally filled with 80/90 GL4. It was arguably the best transmission I ever drove. Tight "snick-snick" into every gear. At about 6k miles I decided time for a fluid change. Went with non-deterg 30 motor oil per J. Esposito. It then became very notchy going into 3rd gear, especially when hot. So, next season I went for the MT-90. All is well again.

It I ever want to save money and go conventional again I would use the Valvoline VR1 non-deterg 20w-50 which I understand is the equivalent weight to 80/90 gear oil w/o the synchro attacking additives.


04-17-2012, 10:39 AM
Roaster factory has a new proper 80-90 GL4 Brad Penn is the name and it sells for 4.61 a quart right now.