replacing the rear main seal in a 67

[Richard G.]

Re: replacing the rear main seal in a 67

William,
I don't want to complicate the issue but I have twice seen leaks back there due to the pipe plugs at the back end of the oil galleries improperly
installed and tightened..

Just assisted a friend of mine in tracing down an oil leak. Turned out to be the same thing (pipe plugs at the back end of the oil galleries) Plug was not as tight as it could have been but also lacked any sealant. We added tape to the fitting and tightened the heck out of it, no torque wrench was involved in this process! We confirmed the oil leak by pulling the transmission and starting the motor with the transmission removed. BTW he had pulled the engine oil pan and replaced the seal prior to this fix. Replacing the seal didn't fix the leak. I highly recommend pulling the transmission for a better look. We had access to a lift and were sure the motor distributor was not hitting the firewall before starting the motor. Be careful of touching the exhaust piping. They get hot immediately, don't ask how I know.
Rick in WA State

[Joe L.]

Re: replacing the rear main seal in a 67

Just assisted a friend of mine in tracing down an oil leak. Turned out to be the same thing (pipe plugs at the back end of the oil galleries) Plug was not as tight as it could have been but also lacked any sealant. We added tape to the fitting and tightened the heck out of it, no torque wrench was involved in this process! We confirmed the oil leak by pulling the transmission and starting the motor with the transmission removed. BTW he had pulled the engine oil pan and replaced the seal prior to this fix. Replacing the seal didn't fix the leak. I highly recommend pulling the transmission for a better look. We had access to a lift and were sure the motor distributor was not hitting the firewall before starting the motor. Be careful of touching the exhaust piping. They get hot immediately, don't ask how I know.
Rick in WA State

Rick-------

The engine plants used a hardening sealer like "Indian Head" on these oil gallery rear plugs. I've never seen or heard of a factory-installed plug leaking. I prefer to use a modern sealer with similar properties-----one that both seals and locks. Teflon tape seals very well but it has no locking properties.

[Mark E.]

Re: replacing the rear main seal in a 67

I've wrongly diagnosed oil leaks more than once. The lesson I learned is to carefully diagnose the source of the leak, and don't make assumptions. Many sources can cause a drip at the rear of the pan. The engine is tilted back, so even leaks in the front will travel to the rear of the pan before dripping to the ground. Clean oil makes seeing its trail even more difficult.

Thoroughly cleaning the engine, an understanding of when and how specific seals/gaskets/threads leak (e.g. Engine running), and using a UV dye and black light (if needed) are good practices for an accurate diagnosis.

[Glen S.]

Re: replacing the rear main seal in a 67

Lots of good ideas here! I changed the rear seal on my '63 more times than I care to think about. I finally discovered that the plugs on the rear of the block that go into the cam galley were where the leak was coming from.

Using a dye and black light to verify where the leak is really coming from is the best approach. I could have saved myself a lot of work had I used that approach.

The last time I had a leak in that area, it turned out that the last person that rebuilt my 4 speed had overfilled it and the oil was coming from the front of the transmission.

There are a number of places that the oil can come from other than the rear seal.

Glen Smith
AZ Chapter