The Stovebolt Site Forums The Shop Area Driveline 235 Rear Main Seal in Vehicle Replacement

I've done a bunch of searches and the rear main seal is a hot topic from time to time. I removed the 4 spd trans from a 1952 3100 that I'm working on, in favor of a T5 installation. The clutch that came out was oil fouled and needs replacement. With that, I may try to attack any seals while I'm there.

I've read some threads where folks say that a rear main replacement, while the engine is still in the truck, is not one that will yield a good result. Anyone have success with replacing their rear main while the engine is in the truck?

Also, where did you buy it? I'm trying to find a vendor now to pick one up.

The only commonly-available rope seal that's worth the effort to install is the Best Gasket seal. Follow the instructions that come packaged with the seal EXACTLY. The OEM seals that actually worked had asbestos in them, and the tree huggers banned that stuff in everything some time ago.

Doing an in the frame rope seal replacement is risky at best, even with the Best Gasket seal. You'll need to loosen all the main bearing bolts a couple of turns to let the crankshaft drop down a little to replace the upper seal. The Lisle "Sneaky Pete" rear main seal kit is just about a necessity to do a successful installation. The seal is over-length, so you'll need to trim both ends of the upper rope flush with the block after packing it into the groove as well as possible. I tighten the first three main caps a little, and rotate the crankshaft to pack the upper rope into the groove, and repeat that process several times before trimming the rope to length. Once the upper seal is in place, then use something round and smooth to pack the lower seal into the cap. I machined an old 4" piston skirt to the seal diameter, 3 7/8". Once the lower rope is packed in firmly, cut it off about 1/32" proud of the cap- - - - -Best provides a trimming guide and a mini box cutter to do that job. They also send a stainless steel shield to protect the crankshaft while trimming the upper seal. Add a dab of non-hardening brush-on sealer like Permatex Super 300 to the joint between the cap and the block. Retorque everything and install the oil pan- - - - -good luck!

FYI: I've replaced dozens of rope seals in all sorts of engines over the past 50-something years, with about a 95% success rate.
Jerry

Fantastic! Thanks for the help Jerry.


Since you've mentioned that you've done a bunch of these, let me ask....have you done these with the engines installed or mainly on the bench/stand?

Back when these engines were daily drivers, if a journeyman mechanic couldn't install a rear main seal before lunch with the engine in the car, he would find himself unemployed. Doing anything short of a major overhaul was always done in the frame back when I learned this trade. I've even seen cylinders bored and crankshaft rod journals reground without pulling an engine. Sometimes I'd dig into an engine and find ONE oversized piston, and/or one undersized rod journal after that kind of work!
Jerry

This may or may not work for you, but it is a different approach and might be worth a try. Actually I tried this about 20 years ago on a 1956 Cadillac and while it did reduce the drip to an occasional thing it didn't eliminate it. I should add I was years later told the remaining leak was probably from a leaking head gasket. From what I understand, these leak predictably back at the rear of the valley pan and mimic a rear main seal.

I once watched a fellow fix a rear main leak in place using a stainless spring steel piece from a windshield wiper blade. It was about 1/8 inch wide and maybe 20 or 25 thousands thick. He measured it in the lower bearing recess and cut it, grinding one end tapered and then rounded that sharp edge a bit. With a small hammer, he slowly drove this between the back side of the upper rope seal and the recess in the block until the ends of the piece he had made were flush on both sides. Then he replaced the lower rope seal in the normal way, put gasket sealer on (the seal piece ends also) and tightened everything back up again.

Good luck!
Jon

Great information guys, thank you!!

I don't want to fool with it if it is not needed, but hard to tell. I'm not sure how long the last clutch was in there, but would really hate to just put a clutch in there and it be ruined soon. I will also take a look around to see if I can identify any other areas of potential leaks.

I have replaced the rear mains on both my 216s while the motors were in the vehicle. I had great success. But I adjusted the clearance on all the main bearings down to the minimums. I used the Best seal and pulled them in with picture hanging wire. I lubricated the seals with the thick Lucas oil additive. I also dropped the rear of the crank by about 1/4".

Is this the real deal gasket?

https://www.ebay.com/itm/Chevy-GMC-...ng-Seal-Set-BEST-1940-1963-/191555289615


I just feel that I need to fix this and any other oil leaks as the inside of the bellhousing had too much oil in it for my liking, when I pulled that clutch out.

That’s it. Good luck.🛠