The Stovebolt Site Forums The Shop Area Engine Shop 1950 3100 Rear Main Leak

I am wondering who makes the best rear main seal for the 1950 3100.

So many different companies and I want to fix correct and not have oil on driveway.

Thanks for information!

If it's a rope seal, the best one is "Best Gaskets." But they depend on a nice smooth seal area on the crankshaft and proper installation. They also offer a 2-piece rubber seal, but I have no experience with those. LINK
If you're doing a teardown for machine work, get the rear main seal area machined to fit a National #417210 full circle seal. That's my plan on my engine rebuild.

Best Gasket

I'm not doing a total engine teardown, just going to have the rear main leak fixed by a local mechanic and figured I'd ask the professionals on here so what to use. Truck runs fabulous but that leak is really annoying. It sat for 18 years in my garage until last fall I got it running correctly but I have no experience with the rear main work. Or do I drive for a while this summer "Live in MN" snd see if it swells back up? Or do I dare use any leak sealer like Blue devil? Or you tell me! Thanks

Installing a rope seal with the engine in the truck will have about a 25% success rate under the very best of conditions- - - - -and that's with the job being done by someone who is very experienced at doing it. Unless your "local mechanic" is drawing Social Security and doing automotive work as a hobby, it's very unlikely that he will have the knowledge or the experience to do it right. I've been pretty successful at replacing only the lower rope seal (in the main bearing cap) and putting a shim made from the thin stainless steel strip that holds the rubber into a windshield wiper between the upper seal section and the block. It's almost impossible to snake the upper rope into place effectively with the crankshaft still in the engine, or to pack it tight enough in there to make a good seal.
Jerry

I'd drive it as much as possible and see if the leak lessens.

How much oil do you have to add and how often? It's sometimes better to leave certain cans of worms closed.

A big cookie sheet with an absorbent pad in it is a lot simpler and less expensive way to keep those oil spots off the driveway. I'll second the motion to do a lot of driving and see if the seal will swell up and minimize the leak. Make sure the pan is big enough to also catch the drips from the road draft tube.
Jerry

I believe these leaks sometimes “scab over” with time. My truck, whether it’s the rear main or the transmission or both…..LOOKS like it’s been leaking for decades. But it doesn’t leave a spot in the driveway.

I’ve avoided “picking the scab.” Not saying that’s good advice, but it’s my approach thus far.

Instead of getting on SWMBO's fecal roster for borrowing her cookie sheet, try one of these from O'Reilly's. 36" x 24"

Like Mom used to tell me, "if you keep picking at it, it's never going to heal".

"If you keep doing that, you're going to go blind!"- - - - - - -"How about if I stop when I need glasses?"
LOL!
Jerry

Thank you so much for the advice. I'll wait until warm weather and get out and drive as much as I can. It's all original my grandpa had it and I was lucky enough to buy it back from the guy that bought it in 1998 after my grandma sold it after he died. Lots of fun memories driving around. Now I can enjoy with my kids. So don't put any stop leak in it all ? It didn't leak horribly this fall but was leaving a couple inch circle after driving 15 miles. But like i said I haven't driven it for many years more like 18 to be exact.

I purchased my truck 3 years ago now and it had been sitting. The rear main seal leaked. I had to change the cardboard under pretty frequently. I was making plans to address it. I was working through other engine issues but the leak was rising on my priority list! After about 3 months of regularly driving, I started to notice my leak was slowing. After about 6 months and 1,500 miles…. No more drips on the cardboard. Then I pulled the draft tube and did PCV mod. No more drips!

Good luck to you

A small circle of oil like you describe is not bad at all. Don't add anything to the oil.

Ok I will certainly wait until spring and drive , what weight oil should I stick to for that pickup? I put in 10w-30 conventional but I want to be sure I'm using the best weight.

Good mention above of the PCV valve. That was a tremendous change I made to my truck a few years ago. Crankcase pressure will challenge seals and gaskets. My truck even ran better with the PCV.

Most of us use 15W-40 Diesel rated oil in the old engines. It seems to do a good job of lubricating, and the 15 bottom weight number seems to be a little less likely to leak than the 10.
Jerry

Well believe this or not but I am not really sure how many miles I have on my 235, but it has to be well over 100,000 and say around 3 or 4 years ago I started using HI mileage 10w 40 valvoline motor oil, not a 100% but I would say it has slowed my leaks down considerably, that was not my intention to use it, but my dip stick seems to stay in a good safe area for months on in.

Since Dallas is normally warm to hot, I use straight 30 weight VR-1 and leave it at that. I have noticed 30 weight seeps less than 10-30.

Ol 55, I use 20w-50 in some of my leakers and it really does cut down on the leakage.

How long you needed glasses Jerry?!!