Gear Oil

[rlich8]

Was going to change the oil in my transmission and overdrive - can I use GL4 85W90 gear oil?

Or should I be ordering Castrol from TRF?

I know I can't use GL5. Just wanted to see if the brand makes a difference, I can't see that it will though?

Thanks

 

[Andrew Mace]

Was going to change the oil in my transmission and overdrive - can I use GL4 85W90 gear oil?

That will be fine (although others will have additional, alternative suggestions/preferences)!

 

[rlich8]

Wonderful. If I can recall properly, I read somewhere it takes about 3 quarts?

I ordered a gallon from NAPA, that should be enough I assume...?

 

[TR4nut]

I think its a little less than two quarts actually - based on the small mess I made when I tried to stuff the last quart in..

 

[TR3driver]

Gearbox is less than 2 quarts for drain & refill; but the rear axle takes most of a quart. So 3 quarts to do both.

Most conventional GL4 oils still use the "active sulfur" additive that can erode "yellow metal"; they just use less of it than the GL5 oils that use the same additive. So my opinion is that it is safer to use an oil that does not use that additive <span style="font-style: italic">at all</span>. Unfortunately the oil manufacturers don't like to tell us what additives they use, so it can be difficult to tell. But from my limited research, it appears that most synthetic gear oils do not use the bad additive.

FWIW, the local O'Reillys has Valvoline SynPower full synthetic Gl5 gear oil for $8.99/quart. I've been using it in all my Triumph diffs for many years, and I believe it provides less friction, better protection and less wear than conventional gear oils. Of course I might be deluded But I wouldn't use it in a gearbox, since they need a certain amount of friction for the synchro rings to operate.

 

[rlich8]

We're all set on the rear axle. I just have to do the gearbox and overdrive now.

Thank all for their help. I'm probably going to use Red Line MT90 then, to be on the safe side.

 

[TR3driver]

We're all set on the rear axle. I just have to do the gearbox and overdrive now.

Sorry, I mis-read your post.

You'll like the MT-90, IMO. It really makes it shift nice!

 

[DNK]

Speaking of gear oil . Hope I'm not butting in.
As everyone knows my car has not been run in about 14 years (TR6). I did some trans work when I had it out and refilled the tranny when installed.
I was under it a couple of weeks ago and noticed there was a couple of drips on the drain (what ever it is). After looking at it I wonder if the PO replaced with the wrong plug as it looks like a bolt from under it.
The question is. Shouldn't it be a pipe thread. I tried to put it in further but it is in all the way and don't want to strip it.
can anyone tell me if this looks correct?

 

[TR3driver]

I believe that is OK, Don. The threads are pipe threads, and that looks like the factory magnetic drain plug (which is also pipe threads). The magnetic plug was not standard on TR6, but is a recommended modification, IMO. It was standard on Stags, and my original one stuck out by about that far when fully tightened.

It's often hard to tell if the plug is actually leaking, since any other leaks tend to run down in such a thin film that you can't see them, and then collect on the plug. But it certainly wouldn't hurt to use some "teflon pipe dope" next time you install the plug, as it will help it to seal. There is also a Loctite product (called PST IIRC) that seals even better than the ordinary dope.

If the plug sticking out bugs you, there are readily available plugs that are magnetic but use a hex socket rather than hex head, and pull down just about flush with the surface. Here is one being installed in my Stag differential (not quite tight yet when the photo was taken)

 

[DNK]

Got those on my other car. Pretty sure it is the plug that is leaking as I cleaned the trans pretty well during the partial tear down.