How to replace '51 M37 rear main oil seal?

[asstor]

Hi All,

I recently got a new toy - a '51 M37, nicknamed "Mater" by my daughter -due to it's rusty, yellow and OD paint job. Much to my horror (or - I should have expected this) I discovered that the rear main old seal was leaking badly - so much that the clutch plate has been destroyed from being soaked in oil (fun!)

It has a split rubber oil seal. Can I replace the rear main seal without dropping the pan and crank or will I be able to get to it if I pull the flywheel? I have the maintenance manuals but they do not specify how to replace the rear main. I may have missed it in the manual though.

Any advice will be appreciated

[Charles Talbert]

Hi All,

I recently got a new toy - a '51 M37, nicknamed "Mater" by my daughter -due to it's rusty, yellow and OD paint job. Much to my horror (or - I should have expected this) I discovered that the rear main old seal was leaking badly - so much that the clutch plate has been destroyed from being soaked in oil (fun!)

It has a split rubber oil seal. Can I replace the rear main seal without dropping the pan and crank or will I be able to get to it if I pull the flywheel? I have the maintenance manuals but they do not specify how to replace the rear main. I may have missed it in the manual though.

Any advice will be appreciated

You will need to pull the pan, and flywheel housing bottom cover. Loosen all the main bearing caps somewhat so the crank can drop slightly downward. Remove the rear main cap completely, half the seal will be on the cap. Use a small blunt tipped punch against the end of the upper seal half. Push upward and it will push right around the crank, grasp the other end of the seal to pull it out. You will find "Y" shaped rubber seals on both sides of the cap, remove them and clean all surfaces thoroughly.

These type of seals are no longer available through Victor or Fel-Pro, we have some new ones on order that should be here by the end of this week. None were available through any auto parts sources as I tried that early this week. We have 4 engine rebuilds going on now, this seal no longer comes in a complete gasket set either. The Fel-Pro has the old style rope seals, the Victor set doesn't have any rear main seal at all. The rope type seals drip, I can't stand that on a new build, so I have run down what appears to be a sole source for the split rubber lip type. These are custom, and we have to get $55 each for them, not bad for a custom seal as NAPA was getting almost $40 each before Fel-Pro discontinued it. We can supply you with one if your luck goes as mine did with local sources.

[asstor]

Charles,

Hey man thanks for the reply. I was afraid that was going to be the answer. I was even contemplating doing it with the engine still in the truck - sucker for punishment. This morning I decided to bite the bullet and went and bought a engine stand. I guess I will be pulling the engine this coming week.

I purchased a full 230 gasket set from Midwest Military, and it included both the front and rear main seals. The rear consist of the two rubber half shells and 4 "U" shaped rubber pieces to seal around the cap. If I hose the installation up (which I have been known to do upon occasion...) I will definately contact you for a replacement.

Thanks for the advice.

This strip down all started so that I could put a fresh coat of paint on the 230 so It's funny how "Oh, it shouldn't take much to get her running again" has turned into a complete strip down. Now I'm thinking if I'm going to drop the pan and loosen the caps I may as well go all the way and do bearings, rings and valves as well. At least I will not attempt to do that with the engine still in the truck!! I am willing to bet it's been done though.

Thanks again

Keep 'em 37's rolling.......

[Charles Talbert]

Charles,

Hey man thanks for the reply. I was afraid that was going to be the answer. I was even contemplating doing it with the engine still in the truck - sucker for punishment. This morning I decided to bite the bullet and went and bought a engine stand. I guess I will be pulling the engine this coming week.

I purchased a full 230 gasket set from Midwest Military, and it included both the front and rear main seals. The rear consist of the two rubber half shells and 4 "U" shaped rubber pieces to seal around the cap. If I hose the installation up (which I have been known to do upon occasion...) I will definately contact you for a replacement.

Thanks for the advice.

This strip down all started so that I could put a fresh coat of paint on the 230 so It's funny how "Oh, it shouldn't take much to get her running again" has turned into a complete strip down. Now I'm thinking if I'm going to drop the pan and loosen the caps I may as well go all the way and do bearings, rings and valves as well. At least I will not attempt to do that with the engine still in the truck!! I am willing to bet it's been done though.

Thanks again

Keep 'em 37's rolling.......

Hang on here. It isn't necessary to pull the engine for rear main seal replacement. I've done many with the engine still in the truck, only takes a couple of hours. The lip type rear seal used to be part of gasket sets, but is no longer included in newer sets, maybe you got a set that has been on the shelf for a while that had the good seal. If the rear seal in your set looks like what you take out, you are good to go, if what is in the set is 2 short sections of black rope material, don't install it unless you want dripping. Just dropping the crankshaft slightly is all it takes to make it happen. Neither is it necessary to pull the transmission, clutch, or flywheel. If you intend to replace the timing cover seal at the front end of the crank, that is quite a bit more involved, but still can be done with the engine installed on the frame no problem. Only 2 "Y" shaped cap end seals are used, upon close examination you will see 2 of the seals fit the grooves of the cap, the other 2 will not, and will be discarded as they are for another engine that shares the same gasket set. In fact a lot of the gaskets in the set will not be applicable to your engine. The remaining end cap area that isn't covered by the "Y" seals needs to be sealed with silicone. Take care not to let silicone get onto the ends of the lip seal or the "Y" shaped seals. Cover the area, but do so sparingly.

If you are thinking of going further into the engine as you mentioned, I would advise pulling it down for a total rebuild. Just doing a ring job will not produce a good long lasting result. Do it right and be done with it. Going half way will likely find you realizing that you are not happy with the outcome and be doing it all over again to get things right.

[asstor]

Charles, thanks for the email. The seal I have is the rubber lip type. I have to replace the front seal as well. Pulling the engine also gives me the opportunity to spruce up the engine bay as well. I have to replace rusted out fuel lines and wiring - so I am going to pull the engine anyway.

Isn't it funny how one can justify just about anything to oneself? Now suddenly I have 10 reasons to pull the engine...!

Thanks for your advice. Once the engine is all spruced up I'll post some pictures. I am going to spray the engine, bell housing and tranny with Bill Hirsch aluminum silver high temp engine paint. It is apparently a dead ringer for the original Chrysler P4529148 engine paint that the T245 wore from the factory - before the army depot OD repaint. At the moment it is the more commonly know caked on RUST color.

[Charles Talbert]

Got the new rear main seals in today

Got a fresh shipment of the correct oil seal kits. We have 4 engines to build currently, but have extra kits if anybody needs one of the correct style. They are no longer part of current production Victor or Fel-Pro overhaul gasket sets.

[asstor]

Charles,

Thanks for the update. I will let you know if I need a replacement seal.