So just swapped in the T56 and changed the oil pan gasket as it was leaking.
Haven't driven 50 miles and oil is dripping down the back of the pan. it looks like it is coming from the rear rubber oil pan gasket seal (very back, not the sides). How can you confirm if it that or the RMS? does it leak from above the pan if it is the RMS or if the RMS fails does it leak through oil pan gasket, hence the name Rear Main Seal and the pan is the secondary seal?
It is leaking quite a bit and already gotten on the flywheel and I had a cover installed. It was made to fit and wasn't perfect, so I'm ordering a new one from a place that custom makes them but still have the leak issue.
Does anyone know the answer to the above? I have searched and can't find.

Thanks in advance!

 

Easiest way is to pull the transmission. With the tranny off and the back of the engine supported, fire up the engine and watch to see where it leaks at the rear. If you can, install a flexplate instead of the flywheel so you can see better. If not possible then remove the flywheel, clean up the back of the engine with some brake clean, reinstall the flywheel then fire up the engine. Let it run for a little while or until a leak is seen then remove the flywheel for better inspection.

If it's a one piece rear main seal, the tranny needed to be removed anyway to repair it. If it's not the rear main seal leaking, you should be able to pinpoint the leak better, repair it, confirm it's stopped leaking then reinstall the tranny.

If it's a two piece rear main then the oil pan needs to be removed for repairs but you should still be able to see it leaking off the back with the tranny removed.

 

Thanks, that is great advice!

Its a 2 pc RMS and the motor was rebuilt only 7K ago, by a shop that has 20+ yrs of experience, so I didn't think it was the RMS. She has sat a 1 and a half when the auto started slipping. Wish I had thought of that while the 700R4 was out, I don't want to remove the T56, have waited a long time to get this swap done.
Is there no other way? I can see it dripping from the middle of the back of the pan but it is hard to tell if it is leaking from above that or if it is just the pan. Or does the RMS leak too much oil to the back of the pan and that pan gasket can't handle it and it leaks out there?

 

Doesn't anyone know if the 2 pc RMS leaks from above the oil pan gasket or if leaks to the oil pan gasket and then out the back rubber section in the middle of the pan?

 

It will leak past the seal along the surface of the crank. The pan only seals to the main bearing cap.

 

Thank you!
So if it is indeed the RMS oil will be along the crank where it attaches to the flywheel, above the oil pan gasket, if not no oil will be higher than pan gasket. I will take a good look and see if it is leaking from anywhere else...

Do the older 2 pcs RMS blocks have a cam plug?

 

Yes.
I'm also looking at a possible RMS leak in my beater '84 305. I've installed a new 1-piece oil pan gasket however what I'm finding is that oil is actually UP inside the bell housing (700R4).
What this is telling me is that oil is getting past the RMS, onto the rotating crank shaft flange and being thrown around. If the leak were strictly from the pan gasket, that wouldn't be the case. I'd thought about the cam plug, oil gallery plugs, oil pressure sender, rear intake manifold seal, distributor gasket in the hopes that it's not the rear main.

 

Thanks, my crank seems dry, but found oil on the flywheel and a drop off oil on the starter gear itself. Going to start her up after cleaning off as recommended above (thanks again) and see where she is leaking from

 

It looks like it just leaking from the oil pan gasket at the back in the middle. This was changed when I did the swap. Frustrating - the motor was rebuilt 7K miles ago and it leaked from the rebuilder, took it back and they put a new gasket and it still leaked after that. Took it back again and they tried to seal it with silicone. Worst part is they installed a new oil pan w/rebuild.
any reason why a new pan won't keep a tight seal to the block on 2pc RMS?

How easy is it for oil to get behind the flywheel and on the clutch?