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TR2/3/3A Drippy Rear diff cover

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Gordon_Dedrick

Gordon_Dedrick

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As one of my winter projects I wanted to fix the small leak I've had since I got the car. I swapped lube to valvoline full-Syn (TR3 Driver suggestion) a couple of years ago with no increase in drips. Pulled the cover, cleaned both mating surfaces completely, powder coated the cover and re-attached with a new paper seal from TRF using Indian Head gasket shellac on ALL surfaces. Tightened bolts down using a crossing pattern, re-filled, and now it leaks worse! Loosing about a half teaspoon each day. Any ideas what I did wrong? Suggestions? This was suposed to be an EASY job!

Gordon
 
I thought the commonly available paper gasket was too thin so I made my own. Just as an experiment I did one car with a gasket made from somewhat thicker paper, the other from cork. Both were fitted using Hylomar. It appears that the thick paper is doing better than the cork but that could be the individual car.

If you have the cover off it is quite easy to use it as the pattern for making a gasket.
 
Did you take a close look at the mating surface on the cover? Many times these get contorted around the bolt holes. Probably a little late (now that it is powder coated) to try to flatten any raised areas. I suggest making your own gasket or using some sort of form a gasket. Those extra thin paper seals will only work on perfectly flat mated surfaces. Knowing the tolerances of these cars, I am not confident that would describe these parts brand new.
Charley
 
I agree with Charley. The cover is almost certainly distorted around the bolt holes, it will take some hammer and dolly work to get it back flat. Should be OK even with the powder coat, if you don't have to move it too far. Use a good straight edge to check that it is flat.

I also like to rub a flat machinists file around on the sealing surface of the diff housing, to remove any high spots around the holes. Don't hold the file by the end as you usually do, but lay it flat and then press lightly on the other side while you only push the file (not grip it) with your other hand. That way, the file will lay flat on the surface, and not tend to round off the corners. The teeth will just slide where the surface is flat, and only cut on high spots, which then show up as a lighter color. I almost always find at least one high spot this way.

Double-check that the bolts are the right length (5/8"). I've found several on my car that have been replaced with 3/4" hardware store bolts that just barely bottom in the holes, meaning they don't clamp the gasket preperly but also don't appear to be loose. Also try a test fit in each hole (without the cover) to be sure there aren't damaged threads or something jammed in the bottom. You should be able to easily turn the bolt in with your fingers, until the gap under the head is thinner than the lock washer. I think TRF has the right bolts, or you can cut down the ones from the hardware store.

As I recall, the gasket I got from TRF was paper, but was fairly thick paper. Seemed to work OK for me.
 
Gordon, make your own gasket out of the paper from a new shirt, or that kind of thickness, use the Permatex ultra gray gasket sealer. Rather than bang on the rear cover, put it in a vise and have two small bits of wood or metal bars if you have them. We get out lots of small dents in bumpers and panels this way, a press works even better.
Did you know if you take a wrench and use the round end, tap around the holes and edge it cuts the gasket as good as it gets. If you have some plastic claps to put around it, to hold it in place, it works much better.

Wayne
 
A lot of the new Dana diffs don't come with gaskets at all. You use the back RTV. It fills any gaps there are and lasts until you decide to take it apart. In fact, I bet you could remove the bolts after it sets and the cover would still stay on forever.
 
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