I have a 1937 GMC 1 1/2 ton truck that has a 230ci Oldsmobile flathead engine. The rear main bearing seal must be replaced. I am hoping I can replace it without removing the engine and crank shaft as explained in the thread in this formum which has been very encouraging.
Would the procedure be the same as for the engine in the thread? Does anyone know if there is a modern seal that can be used as the replacement, and if so, where it can be obtained? Any advice or assistance would be greatly appreciated. Thank you in advance.

I have no experience with that engine, however, I see no reason why the seal can't be changed in the car. I'm sure you won't find a modern seal to fit your engine. It isn't popular enough for a company to make a neoprene seal for it. It's all based on supply and demand, and there is no demand for your engine.
Back in the day, most engines had the rope seal. There is an inexpensive tool called a "Sneaky Pete", that you should be able to obtain from any auto parts store. it is designed for replacing the rope rear main seal in the vehicle.
I described this tool in an earlier post, but I'll give it a go again. It consists of a small diameter rod, with course threads on one end, and a quarter sized loop on the other end. It maybe eight inches long. The threads are course, like a drywall screw. You drop the main cap, and screw the threaded end into the rope seal, between the crank and the block. Screw it in as far as you can. Then, as you slowly turn the crankshaft, you pull the rod in the same direction, and the seal should come out. Stick a screwdriver or something through the loop on the end as you pull and turn the crankshaft, preferably with a flywheel turner. Pull and turn slowly, and the seal should come right out.
The other part of the tool is basically "Chinese Fingers". You stick the end of the new seal in the metal mesh "Fingers", and as you pull on the fingers, it grabs the end of the seal. Grease the heck out of the seal, and push the other end of the fingers up and around the crankshaft, then slowly turn the crank and pull the tool, which is attached to the seal, at the same time. If you don't understand what I mean, go buy the tool and look at it, you will understand what I'm saying.
Go slowly and keep the seal lined up and it should pull into place. The seal will be a little long, and need to be cut off flush after you get it into place.. I cut them a tiny bit more than flush, so when you put the two ends together, you have a slight crush on the seals. I also put a dab of silicone sealer at the seal joint. The top half of the seal in the cap half is easy. Put the seal in place, crush it down by rolling it with a large diameter socket, or similar item, then cut it off a hair over flush.
It takes some time and care, but you can do a good job and it shouldn't leak. The rope will never be as good as a neoprene one piece seal, but life aint' always fair...!
Here ya go, a Sneaky Pte for $8 bucks.! you'll be sailing aloong in no time....
http://cgi.ebay.com/ebaymotors/LISLE-Sne...ZWDVWQQtcZphoto

RocketDude - Thank you for your help. I just bought the tool, so now I'll get the seal and get started. This thing has been leaking so badly I had to hang a can under the engine to catch the oil. It will be great to get this fixed. Thanks again.

please consider my advice.....This will depend on the shape of the seal once you take the cap off.If it has been spun around with the crank,then it does not apply.If the upper seal-assuming it is a rope seal-has been put in originally with the crankshaft out of the engine,it is a slim chance that you will be able to fish a new rope seal in there that will seal any better than whats there now.Unless of course,the rope was put in poorly to begin with.Once you forge ahead and try to fish that top rope out,you will see what I mean.Not saying that it can't be done,but it would be a lot easier if the motor was upside-down and you could really stuff it in there.Its the top of the seal that doesn't get compressed enough,just because the rope isn't rigid and wants to bunch up.Of course we are also assuming there is no huge play in the main bearings.
Consider replacing only the lower rope and follow regular procedures allowing for some squishing without getting material caught between the two halves of the cap.

Pete - Thank you for your advice. I share your concerns. I'm also afraid that the upper half of the seal might break apart as I'm trying to pull it out and that would ensure I would have to pull the engine. Replacing just the lower half would certainly be something I could try first. I've also heard that there are some "shims" that can be pushed into the groove above the upper seal to compress it toward the shaft to improve the seal. Does anyone know anything about these and where they could be obtained? Thanks for your advice and help.

Changing just the lower half is certainly something to consider, if you don't mind the extra labor if that idea fails. Once you get the cap off, it should be obvious if that is where the leak is. The biggest percentaqge of the time, it will be the lower half that leaks, so your chances of success are good. If that isn't the whole problem, it has to be at least 50% better, so the catch can size can be reduced....!

I have seen this topic covered before by a mechanic thru a web search when I was interested in this procedure.The idea is to sharpen flexible wire(s) and drive them behind the seal.Seems logical to me though I ran the idea past a mechanic and he scoffed at it.I feel it has merit though and a souce for the wire might be a choke cable wire-flexible,yet strong and won't kink easily.Wish I knew more about the motor you are working on however since a newer type seal may fit but no one has bothered to share that information.I was lucky to obtain a new-type seal for my 324 olds and it slipped in there so slick,I couldn't imagine getting a rope to suffice.Let me know once you get a look at the thing and how you make out.Remember that you will need a torque wrench anyways to tighten the cap.....maybe consider removing the crank.The time factor is a biggy but may pay off in the end.

Pete - Thanks again for your thoughts. I thought the procedure called for a flat piece of steel similar to a clock spring that could be sharpened on one end and then pushed/tapped into the groove behind the seal.
I think I've pretty much decided to try replacing just the lower half first. Leaving a slight protruding stub on each end of the seal will also tend to compressed the upper half when the cap is pulled up tight.
Pulling the engine on this truck is very difficult. It is a Cab-Over so there is no way to hook onto the engine and lift it straight up. It has to be eased forward and up at the same time. I can see where it was done before and they cut part of the firewall out to give them better access, and then welded the piece back in after the engine was replaced. Someone has suggested removing the transmission so the crank could be lowered just a bit while still in the engine in the truck.

well it sounds like you've got a good grip on things.I mentioned the choke wire(solid,not stranded) because thats what I used to remove the upper seal on my olds-drove it in and made a hook on the other end and then pulled it back-vise grips are essential.I wonder if you could put the upper seal in smaller pieces-at least you could stuff it in there better.Sounds crude but remember there already is two breaks in the rope.The only other advice I can suggest is to contact the Best Gasket Company and ask if they have any recomendations since they make the newer type seal for the 324.Other source could be EGGE engine-seem to have a lot of connections as well.

Well it took a while, but here is the rest of the story:
I removed the main bearing cap and replaced the lower half of the seal. At that point I decided I did not want to put it back together with only half the job done, so I went after the upper half. I had the Sneaky Pete tool I had purchased, but I could not get the cork screw removal tool screwed into the seal. The point on the end of the cork screw was pointed in the direction of the spiral and I could not get enough force in that direction to get it started. I then drilled a small hole in the end of the seal and screwed a dry wall screw into it. I gripped the dry wall screw with a vice grip, and using a home made tool to turn the crank shaft, I pulled the upper half of the seal out.
The installtion tool has a small metal clip with opposing teeth that are compressed into the seal as it enters the seal groove. Problem is, the teeth are only about half an inch from the end, and as I tried to pull it into the groove, the teeth shreaded the end of the seal and pulled out. (I was turning the crankshaft at the same time.)
I bought another tool (KD) which was a bit more money, but the installation tool was the chinese finger type which compresses more as you pull on it. Initially I had a problem because the seal bulged out between the wires of the chinese finger tool and would not enter into the groove. Then I realized the KD set included a plastic funnel that the seal can be started into at the work bench. As it exits this funnel, it is compressed and it therefore enters the seal groove as it should. After that, the important thing is to be carefull when trimming the ends of the seal. Each end should be trimmed slightly "proud" so that the ends will be compressed when the cap is replaced. After I installed the cap, I removed it and looked for threads that might have been caught between the bearing cap and the crankcase. I found a couple and timmed them off.
After I started it, there were no drips, but after it got hot it started to drip. I later realized that it was just residual oil on parts from the previous leak getting hot and running down. Now it appears that the leak is fixed. Thanks to everyone who offered suggestions and help.
PS - The KD kit also had a better removal tool.