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1979 Town Car Rear Main Seal Leak

Hi Bill –
my mechanic is flummoxed by an oil leak at main seal (rear) in my 79 Town Car with 400 engine. He has replaced the seal three times to no avail (used two different brands). He also questions the notches on the crankshaft, wondering if these contribute to the problem. He thinks maybe a rope seal was original. Any words of wisdom for us?
Hi Larry –
Some of these oil leaks can be frustrating at times. I am surprised though that your mechanic has you the customer searching for the answer to his problem with your oil leak. Usually experienced engine repair mechanics have local engine machine shops that they deal with and to consult with. Check first to be certain that the leak is actually caused by the rear main engine seal and not the oil pressure sending unit located at the top rear of the engine. An oil sending unit leak can appear under the engine as a rear main seal leak. Next examine the crank at the critical seal area for excess wear etc. that could cause a poor seal and leak.
Do you know if the rear main bearing etc. was gaged for proper clearance and then replaced with a new bearing set of the correct thickness and fit for the crankshaft. Bearings at this location with too much clearance are known to allow too much oil pressure to leak towards the rear main seal area and cause leaks. All of the above are only suggestions from our experiences. It may be a wise move on your part to have an experienced engine machine shop mechanic look at this situation while it is apart. Problems such as this usually require an on-scene inspection.
If the above suggestions are applied and the replacement parts are correct and installed correctly the engine should not leak from the rear main seal. We wish you and your mechanic the best of luck in correcting this issue. Please let us know what you find.

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