Need Help with a 1935 Pontiac - Rear main bearing seal leaking

[skipsmustang1965]

I am new to the AACA and to this forum so any help would be greatly appreciated. I recently purchased a 1935 Pontiac and it's a super cool car! It has been leaking some oil which I kind of expected for an eighty year old girl. Did some investigating today and the oil is leaking out of the flywheel cover so I suspect the rear main bearing seal is the culprit. I know this can be very labor intensive so I was wondering if anyone has suggestions for a temporary fix such as these No Leak/Stop Leak oil additives? Has anyone ever had success with these type of products and if so which one(s) work the best?

Thanks for helping out a Newbie!!!

[Dave Henderson]

The rear main bearing seal on these cars is a rope impregnated with graphite and compressed. When it is worn out there is no quick fix. It can be replaced without removing the motor or crankshaft. To do so the pan must be removed, the rear cap removed and the other mains loosened. The section of the old seal in the cap can easily be removed, but the part in the block isn't as easy, try needle nose pliers to pull it out. Pushing it usually doesn't work. The slickest way to install a new one in the block is with a "Chinese finger pull" devise which you first push around through the groove, then attach to the seal part and pull through. The new part for the bottom cap should be worked into it's groove and compressed some for a tight fit with an appropriate cylindrical object. Then, the excess projecting portion of both should be trimmed.

An interesting feature of the '35's rear main cap appears in a period Motor's Repair Manual. It states; "1935--a ball check oil drain-back is used in the rear main bearing lower cap with the opening to the front. The angle of the tapered hole is downward and unless the car is on an incline greater than 10 degrees, the ball check is forward in the open position and the oli returns to the oil pan in the conventional manner past the ball check.

However, when the front of the car is elevated to an angle greater than 10 degrees, the the ball rolls back and seats in the tapered hole, thereby preventing loss of oil at the rear main bearing". (Make sure the ball isn't stuck from sludge).

Excess bearing clearance will also cause rear main oil leakage. You should probably check the clearance using plastic gauge, and if it is more than .002 ( two thousandths of an inch), the mains, which are removable inserts, could be replaced, or, the way I did it on my jalopy '35 Pontiac as a high school boy in the '40's was to cut a shim from brass shim stock and place it under the insert in the bearing cap, but don't do that if the insert is worn through to its lining. Also be sure you haven't locked up the crank from too much shim thickness. Wow, a '35 Pontiac, my very first car! Good luck. Dave

P. S. Something I just remembered, cigarette rolling paper was also sometimes used for shims, really, and vasoline was smeared on the crank surface for lubrication during start up.... those were the days.

Edited February 14, 2015 by Dave Henderson (see edit history)

[skipsmustang1965]

Thanks for all good info Dave!

[Robert G. Smits]

Interesting that my 34 eight cylinder has a similar problem which continued after replacing the rear seal. I must admit that I didn't check for bearing clearance 20 years ago. The car performed flawlessly on Glidden #34 other than losing 1/2 quart of oil per day I am thinking about taking it on this years Glidden. Has anyone converted to a modern seal? Thanks, Bob Smits