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TR2/3/3A Tr3A rear main seal conversion - adviced needed


Jedi Trainee
I had my crank turned to the recommended dimension and installed the new type seal. After driving it for a short time the seal began to leak.
I used all the parts and installed them as recommended by Moss. The only thing I might have done is to use a Silicon that cured to quickly. Moss recommends a non hardening sealant. I used Permatex Ultra black.
Do you guys have any special technics that you use when installing the new type seal? Don't want to go through this again for a while.


Did you soak the felt packing in gasket shellac and pound it in around the two aluminum pieces that hold the rear seal in place? Even with a modern lip seal, you still have to do this.

Silicone around the outside of the seal should be fine. Silicon (sand) would not be OK. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

A while back the machining dimension in the instructions sent out was incorrect at 2.500" instead of 2.5+ a little"

A fix that will sometimes work is to increase the force on the seal around the crankshaft. To do this, you'll have to remove the spring that sits inside the rubber seal and cut off a couple of coils, then resinatall it. It will squeeze a little harder and eliminate the leak (maybe).


Jedi Trainee

I am not sure what you mean by felt packing? The rear main bearing cap has seals on both ends. I made sure they were soaked and sealed well.

As for the dimension, I had the crank cut to 2.5 +.005/-.000 as the instructions recommended. If they were wrong then I'm probably going to be very upset with Moss for not changing the dimensions.

I just finished replacing the seal for the second time. This time I made sure it was in place and was sealed well. I started the engine and reved it for a few minutes. So far so good.

Thanks for your posts...


The rear main bearing cap seals are made of felt. They give you two pieces but it's really not enough for a good seal.

The manual says to cut the felt into 1" long pieces, soak them in gasket shellac and use a drift to tightly pack them around each side of the cap, let dry and cut off the excess. It really takes a lot of force to push them all the way to the bollow of the cap. Many people have had leaks because they don't tap the pieces in far enough to seal the bottom; if you tap the pieces in far enough to create a proper seal, you end up needing more felt that originally supplied. Two pieces is usually not enough.

If the scroll on your crank was cut to 2.50 +.005, you should be all set.


Jedi Trainee
I got everything back together yesterday evening and started the car. I let it run for 10 minutes while reving the engine a few times after it got hot. Turned off the engine and waited for ten minutes. No drip. I got up this morning and checked under the car and there was oil again.

Got a flashlite and looked around and it looks like the same problem. Although I could see oil running down the back of the transmission bell housing.

I installed the seal taking my time and making sure the ring, spring and seal caps were aligned and tight. Made sure the cork seals fit well and were sealing properly. Prefitted the seal and made sure it was closed and sealed well.
Honestly don't believe it is the main seal this time. I think the valve cover is leaking. The cover is somewhat smashed from someone else tightening it too tight.
I may order an aluminum cover to make sure it seals well.


Jedi Trainee
I didn't remove the front main cap to do the second installation. However I did replace the front seals when I did the crank two weeks ago.
As for the back ones I reinstalled the felt ones and resealed them properly.
I'm also at work and won't be home until later so I'll have to check for leaks then... I sort of believe the valve cover is leaking but am not positive. It shouldn't have taken a long time to leak if it was the main of the crank cap seals.

If I get this one fixed I will finally be able to enjoy the car.


Great Pumpkin - R.I.P
Note that there are a couple of other places that might leak oil and drip from the rear. There is a soft plug in the end of the cam bore (inside the bellhousing), plus a threaded plug on the back of the head and others.

In my case, much of the leak proved to be from the bottom of the fuel pump. The flex line to the oil pressure gauge was also a culprit.


Jedi Knight
I believe i read that Greg Solow in calif. tried all the seal kits with poor results and then modified the original scroll seal to take a mopar seal and no more problems.I think he added weld to the scroll to increase the diameter and no more problems.I have not bought one of the "modern" conversion kits since i have read so many mixed results about them.


Larry, you can pull things apart again. Or you can source where the leak is coming from. How? Leak Detector Dye.

Used to have to buy a several hundred dollar kit from the tool truck with a great big searchlight type light. No need any more.

You can go to your Napa store(probably carquest has them also. And get the little penlight flashlight and the yellow sunglasses that pick up the dye from the leak dye for under $30. You can get the bottles of leak dye(a/c, coolant, atf, engine oil) from almost all parts stores(Napa, etc.) and just about every tool truck you see floating around, from 8 to 15 dollars.

This way you can put in the dye, run the engine for 10-15 minutes then PINPOINT the source of the leak.


Jedi Trainee
Guys, wish I found this sight in the Winter before I started my car. As the the gentleman from Maine discussed I think it is the rear main cork seal.
I can run the motor for 15 minutes, look under the car and no leak. Let it sit for an hour and a small puddle appears. When I look into the tanny/engine mounting area it is seeping down from the end of the oil pan like it has run down from the sides of the bearing cap on both sides.
I guess I failed to know the importance of the seal. It is there but perhaps not as sealed as it should be.

Anyway, if it will stay at this small amount I'll enjoy the car for a while until I decide to try again.

Thanks again
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