Differential gasket replacement question

[doughairfield]

The rear differential on my TR4 is slowly leaking lubricant due to the puddle accumulating in my car port. I'm pretty sure it's not where the drive shaft goes into the diff. Is it as simple as draining the fluid and replacing the gasket, then putting cover back on and and torquing to the appropriate value? Or is there something more once I get that cover off that I would have to do?

 

[NickMorgan]

I think that is about all there is to it. You will probably want to put a thin smear of something like Wellseal onto either side of the gasket.
I am not sure if the TR4 has the same clip as the TR3, holding the brake line onto the rear diff cover. I have been told that there is enough movement in the brake line to allow the cover to come off. Make sure that you remove all traces of the old gasket.
The pinion seal on the front of the diff is also a possible leakage place. It is worth checking where the oil is leaking from before replacing the gasket. Shame to have to drain it all again to replace the seal!
I have these jobs planned this coming winter.

 

[doughairfield]

Thanks Nick. I'm pretty sure it's not the pinion seal, at least I hope it's not. I used permatex on when I replaced the gasket on the oil pan, so I was planning on doing the same procedure on the rear diff cover. remove, clean, prematex on the gasket, allow that to cure, then put it back on.

 

[davidk]

On my TR-6, I used Permatex Right Stuff with no gasket. No leaks so far....

 

[doughairfield]

Does anyone have a suggestion as to what kind of fluid to refill the differential with once I get the cover back on?

 

[TR3driver]

I like Valvoline full synthetic gear oil . Can't prove it's any better than anything else, but my TR3 diff was already well worn when I got it in 1984 and hasn't gotten any worse in perhaps 200,000 miles.

 

[doughairfield]

Randall, et al. Is there any risk in using the synthetic gear oil and damaging any seals in the diff? I picked up the Mobile 1 brand synthetic gear oil and was going to refill the diff, but a friend said to be careful using synthetic in a car that whose seals were around before synthetic existed.

 

[TR3driver]

All I can say with any certainty is that I have never noticed any problems of that sort with the Valvoline gear oil. It's in all my Triumphs, and I've never changed seals just to convert to the Valvoline.

But I had a bad experience with Mobil 1 <span style="font-weight: bold">motor</span> oil recently, it leaked far worse than the SynPower did (in the same grade/viscosity) in the same motor. It may be that Mobil 1 gear oil would do the same, I don't know (and I don't care to find out).

But the consumption rate went back down when I switched back to SynPower (actually just started using it to top up after the Mobil 1 leaked out), so I wouldn't say it damaged the seals. Perhaps it's "seal sweller" additive isn't as effective or something.

 

[doughairfield]

Interesting. I will take it back and try to find the Valvoline. Any recommendations as to the torque for the bolts when I put the rear diff cover back on?

 

[TR3driver]

The TR3 book says 16-18 ftlb.

 

[doughairfield]

I confirmed with a coworker, that mobile 1 seems to have a leaky reputation. He recommended the Brad Penn, Grade 1 Racing Oil; 20W50, Partial Synthetic. It apparently has some secret sauce that cuts down on the leaks.

Randall, what weight gear oil do you recommend for the rear diff? I'm gonna fill her back up tonight.

 

[Geo Hahn]

As for the gasket... you may be better off making your own from gasket paper rather than purchasing one. The one I got from Moss was clearly for something other than a TR4 diff... perhaps a 4A? I pitched it and made one -- dead easy as you have the cover to use as a pattern.

Yes, I should have probably told Moss about the problem (per prior thread on parts quality) but I didn't. Had the right part number but may have just been mislabelled.

 

[doughairfield]

I purchased my replacement gasket from VictoriaBritish, and it seemed to match up perfectly with one exception. There were 2 extra screw holes, maybe to accommodate the TR4A. But with the red permatex around the cover and the gasket on top of that, it fit just fine.

 

[TR3driver]

Probably too late, Doug, but I use 75W90 gear oil in the diffs.

On the TR, I just used RTV for the cover gasket. On the Stag, the gasket I got from TRF fit perfectly.

 

[doughairfield]

Ah, not to late at all, been waiting on the permatex to cure before I put the oil back in. And I need to go switch out the Mobile 1 for that Valvoline you suggested.

That and I am still working on that voltage regulator problem, that I also posted about, hint hint ;-)