Shimming a main seal with wire

April 1, 2008 | By Staff


In the June 2007 issue, reader Leigh Santos said he was having a problem with a leaking rear main seal on his 1941 Oldsmobile. You said you couldn’t be sure what technique his mechanic was going to use to install a new seal with the help of some piano wire, and I want to share my experience with that situation.

Back in the mid-1960s I had the same problem with a 1954 Ford with a 239 cid ohv V-8. It had a reground crankshaft and undersized bearings. After a few thousand miles the rear main seal started leaking quite a bit so I installed a new one. I used a heavy work shoe shoelace to pull the new seal through while I ran the starter motor.

That greatly reduced the leak for a while but then it came back as bad as ever. If I remember correctly, the seal rode on the main journal and I theorized that, because it was ground undersize, the seal rope was not getting sufficient pressure exerted on it to seal properly.

I read in an auto manual somewhere that a seal could be shimmed up with a strip of stock placed in the bottom of an engine’s seal groove, but to do that I would have had to do some major dismantling of the car.

At that point I came across an item in a technical column similar to yours, and they claimed there was a kit on the market to install steel wire under a seal to shim it up.

This got me to thinking and I obtained the tempered steel wire out of a heater cable from a junk car and dropped my pan for about the fourth time!

I clamped a length of the wire about six inches long in the end of a Vise-Grip with about 3⁄4 inch protruding beyond the jaws, aimed it into the bottom of the seal groove, and began to drive it in by tapping on the end of the Vise-Grip’s adjustment screw with a hammer. As the wire went in, I kept re-clamping the tool another 3⁄4 inch down the wire until the end finally emerged in the bottom of the seal groove on the opposite side.

I then snipped the other end off so about 1/8-inch protruded on each side and put everything back together. The leak stopped right then and there!

The only problem I could see with this was if the wire went through the seal somewhere and contacted the crankshaft journal surface. There would be no way to determine that until the damage was done. Unfortunately, I have no real longterm data for this fix because about eight months later I took the 239 out and put in a 312 cid engine.


Well Chris, it’s difficult to argue with your success!

I have never tried the technique you describe, but based on your experience it apparently works in at least some instances. Thank you for taking the time to share your experience with other readers.