The Stovebolt Site Forums The Shop Area Engine Shop Rear main seal

Now that I fixed all my electrical problems and installed my new radio its onto the engine leak. My engine leaks just past the rear of the oil pan. The oil comes through a small hole on the rear cover before the tranny. I have been told its the main rear seal.
I read the tech tip on replacing the rear seal. The wick type seams more invoved you have to remove this and that but with the neoprene seal you don't have to remove the oil pan or pump is this right or did i miss something in the translation.
I have a 235 6. Can I get the neoprene seal for my truck and do I get it through say Napa or someone like that. Do the seals always go on these trucks. I read the seals leak at a continuos high speeds my manual said that. Any help here would be appreciated Thanks Peter

you might be able to use an additive to rejuvinate your seal. These engines are tricky to seal. You will have to drop the oil pan. Does the engine have any other problems? If it does it might be a good time for a complete overhaul. If it is not leaking to bad, you could put one of those oil pans under it when you park, and carry a couple of courts of oil behind the seat. Check your oil level at every fill up.

If these old trucks aren't leaking oil, they are probably out of it.

Replacing the rear seal is quite a job, especially if you don't want it to leak again

What additives are availiable to rejuvinate the seal. It doesn't leak alot but its a pain. Any other thoughts

Here's how I see it. If you are getting oil in the transmission cover then I would want to go through the clutch. In order to go through the clutch the transmission has to come out. If the transmission is out then I would want to remove the flywheel and get that resurfaced before replacing any clutch parts. So now the only thing left is pull the front sheet metal and the engine is sitting there wide open on the frame. Pulling the engine from there is a cinch. Then you can rig an engine stand or borrow one and replace all of the seals with the engine out of the truck. To me the hassle of replacing the rear-main on an old engine is just not worth the effort. For another week or two you can replace all of the seals, flywheel, and clutch kit and be done with so many other potential problems with only a fraction more effort. But then I'm just a dumb old guy from San Diego.

The engine has been rebuilt along with the tranny. Sorry i didn't mention it. It still the rear main seal leaking my question is the tech tip said it seem easy to do and I want to know about the neoprence seal. Also does any one know about the additive I could get to maybe seal the seal or AM I dreaming here.
Years ago I used a sealer on my radiator it worked like a charm the main ingredient believe it or not were walnut shells no lie.

Petmil,

My personal opinion for additives to rejuvenate any seal is this:

They "might" work to soften up the neoprene seal and help things along for a short time. They won't fix the problem. I don't think an additive is going to do squat for a rope seal.

I wouldn't believe the rope seal is never going to seal adequately. Since you just had your engine rebuilt, that might be the testament for my last remark.

I don't know how you are ever going to rejuvenate a rope seal. I think they would be very hard to get out, and more so going in, without pulling the crank. I have never done it with the crank in place, but rope seals are in there pretty tight. Some are anchored with a pin also. I would think that would be hard to deal with also.

On the V8 engines, the neoprene seal replacement will ride on a new surface of the crank (I cannot claim the same for the 6 cyl.) and not on the rope seal surface. The rope seal surface of the crank is usually pretty worn and that surface is not used with a neoprene replecement.

If I were going to replace the seal with the motor in the truck, I would DEFINETELY go with the neoprene at this point.

mmmmm Another opinion any more. peter

I had very good luck with the Napa neoprene seal on a 56 235. It was a major leaker before. It has been holding and is completly dry after 4 months. It is somewhat difficult to get the upper half of the old rope seal out but it is worth the effort.
Fred

rfs56trk, what was hard about removing the seal? Was it pinned or just hard or just stuck or what? I gotta do this on my 54 235 and am wondering... randy

thanks rfs56trk did you do it your self anyone else. peter

rmillburn ... I tried removing the upper seal from a gmc 270. I got one of those sneaky pete tools that screws into the old seal. It wouldn't budge. I then loosened up the journals that support the crank, and it still wouldn't budge. It was then I decided to pull the engine, and do it on a bench.

Look for the sneaky pete tool first. They also have a "Chinese Finger" tool for getting the seal back in.

You Chevy guys are lucky. I don't think there is a neoprene seal that will fit the jimmy engines

The pan which covers the bottom of the flywheel has a hole I guess for obvious reasons, to let oil drip out. If it is a quarter size drip after each ride you probably can live with it. Way back when these cars and trucks were on the showroom floor they had "GM Authorized" cardboard mats sitting under the engines to catch drips.
Some people and manuals suggest that after removing the rear main cap you might want to loosen the others so the crankshaft will drop a bit. This is supposed to make getting the upper half of the seal easier to remove. I did not have to do that, thankfully. As mentioned my old neoprene seal came out and the new one went in very easily because they had dried out. The whole job from the time the pan came off until I was ready to reinstall the pan was less than 30 minutes. I had more difficulty getting the oil pan to seal.
While you have the pan off how is the seal and gasket at the timing gear cover?
Bill

I have been checking out ebay for a seal for my 56 235 and found a seller that had a bit of information about the subject. According to him the neoprene seal was introduced in 1956 and all previous years came with the rope seal. The machining tolerences on the pre 56 were different so the neoprene may or may not seal properly. The ebay number is 8051264644 if you want to read it for yourself.

I have a tool from an old tool set, probably similar to what was described as a sneaky pete.
I threaded the tool into the seal and pushed on the opposite side with a small wood dowell. It took two attempts but it came out. I didn't loosen up any other bearing caps but that is not to say yours will work that way. You could probably make a tool as it is little more than a rod with a bend in it for a handle and threaded on one end. Keep it away from the crank so you do not inflict any damage. Fred

rfs56trk,

Does the neoprene seal ride where the old rope seal rides on the crank, or does it contact the crank in a new position on the 6 cylinder?

I think Bob Adler wrote an article about this tool some time back in Vintage Truck. He has a link on this site and can be contacted quite easily via email. He probably has a copy of the article. I think he goes under Adler Antique Autos.

Here is my experience, replacing the rope seal with the motor in place. I was unable to remove the top seal with the crank in place. I tried backing off the rest of the mains but the transmission would notr allow the crank to drop enough. This was an experiement because I was intending on taking the tranmission off anyway. With the transmission, front cover and flywheel off, you can pull the crank down quite a bit to do the job.

The neoprene seal is not meant for the early motors.

Builder,
The new seal fits into the same space and is held in to the groove just like any late model lip type seal. It essentially rides on the same part of the crank as the old rope seal. Fred

Well when I was in The US last week I bought some cd-2 Sealer for my truck I will report back to everyone on how this works on sealing things up. I'm going to change my oil and then add the sealer I'll be back to you all.

BTW where do you put this sealer? Into the oil? Would it not seal everything if it is in there. My concern is the oil pump.

My understanding is the sealer swells the seal or makes them softer so they do there jobs I guess i'll find out I'm waiting to change my oil first. peter

It goes in the oil. It will soften up the seal so it wil become pliable. Once the "old" seals are pliable they wear out at an accelerated rate.

What if anything it will do to a rope seal is a good question. My guess is that it will do very little of anything.