View Full Version : Definitively Diagnose a Leaking Rear Main

08-19-04, 04:26 PM
I suspect that my rear main is leaking. Is there a definitive way to diagnose this before I go through the trouble of changing it. Everyone says "Oh if you have oil leaking from the rear of the engine, it's a rear main". I'd like to know for sure. Thanks.

08-19-04, 05:37 PM
Had the same prob on my '68 472. My rear main was leaking... really badly. There was oil all over everything south of the rear of the engine. If you can see the oil coming out at the seam between the tranny and the engine, it's probably the rear main.

08-19-04, 05:58 PM
Thanks. Did you replace it yourself or did you have someone do it? I've been reading up on it and it seems like the hardest part is going to be to drop the pan. Any tips?

barge master
08-19-04, 09:33 PM
You're gonna have to raise the engine.The best way I've found is to do it with a hoist from the top. Just watch stretching the wires and hoses. The fan will have to come out because it will hit the shroud. Those little mesh finger gripper gizmos are the easiest way to pull a rope seal through. You'll need a torque wrench for the bearing cap. An anaerobic sealant like Hylomar is a good idea around the edge of the seal, where the cap and block will meet. And it is a huge pain in the ass to do, esp. on the ground. Have fun!!!

08-20-04, 01:13 AM
The rope seals are OK, but see if you can get a two peice neoprene seal. Make sure its the two piece kind, the one piece involves much more work to install it correctly.

08-20-04, 11:00 AM
the 472 /500 motor does not use a rope seal ........... and though it could be a bad main seal my guess is that it is the rear pan seal that is leaking ..... but if you are going to the trouble to pull the pan a rear main is cheap just remember to torque the cap back into place and to put a little oil on the seal before you put it in .........

08-20-04, 12:18 PM
You're gonna have to raise the engine.

Thanks for the info. The shop manual doesn't mention raising the engine for my car (69 DeVille), but it does specifically say you have to do it for an Eldo. Anyone done this without raising the engine in a DeVille?

I searched some other posts on this board and someone mentioned that they were able to get their pan off on a 68 DeVille w/o having to raise it.

Once again, thanks for the help.

08-24-04, 03:38 PM
If you haven't already, check the oil pressure sending unit. Have seen quite a number of leakers. Top rear of engine behind intake manifold. Who knows, you might get lucky on this one.