mtl92 Posted April 4, 2023 Share Posted April 4, 2023 Hello all, I was hoping some one could give me some instructions on replacing the rear main seal without removing the crankshaft if that's even possible. I think I have a sizable leak coming from there. Thanks in advance for the help! Link to comment Share on other sites More sharing options...
Bloo Posted April 4, 2023 Share Posted April 4, 2023 (edited) You will probably need the shop manual for that. I don't recall what year they started using a seal. My 36 does not have one. It has a slinger and a drainback pipe and I need to not park on steep hills like the ones they have in San Fransisco. If it has a seal, it is most likely a rope seal. You can indeed change a rope seal in the car. There is a tool called a "Sneaky Pete", probably still made, that allows you to pull in a new top half of the seal with the crank still in place. Pontiac flatheads also have "seals" along the sides of the lower main bearing cap, another possible source of leaks. On my 36, they are wooden sticks. I believe Pontiac was still using the wooden sticks in 1940, but that is another question for the shop manual. If there's a seal, and you change it, you will also be doing the sticks because they come out with the main bearing cap. If the main bearing is too loose, that can cause more leakage. I'd plastigage it while I was in there. Main bearings can be changed in the car too, one at a time. My 36 manual shows how to make a tool from a cotter pin to accomplish it. Also, later Pontiac flatheads have a centrifugal(?) oil filter in-between the oil pickup and the oil pump. It just causes the oil to change direction suddenly and particles of crud keep going straight into a trap. When the cars were new, that filter was meant to not need service until the car got to 100.000 miles. You probably have a filter like that on a 1940, I think. If you have the oil pan off, be sure to remove the filter, disassemble as necessary, and clean it out. Good luck with it, and welcome to the forum! Edited April 5, 2023 by Bloo (see edit history) 1 Link to comment Share on other sites More sharing options...
mtl92 Posted April 5, 2023 Author Share Posted April 5, 2023 Thanks Bloo! I'll check out this sneaky Pete and see about getting those bearing cap seals as well. I appreciate the info! 1 Link to comment Share on other sites More sharing options...
49 Streamliner Posted April 5, 2023 Share Posted April 5, 2023 (edited) My '49 also has the slinger and a drainback pipe and wooden sticks that Bloo mentions. If yours is a 1940, it probably does have the same features. Replacements for the sticks came from California Pontiac Restoration. Mine also has the internal oil filter. When the oil pan was off last year during some engine work, the filter and pan were filled with crud. Here's photos before and after cleaning the filter. Bill Edited April 5, 2023 by 49 Streamliner additional information (see edit history) 1 Link to comment Share on other sites More sharing options...
mtl92 Posted April 5, 2023 Author Share Posted April 5, 2023 That's a huge difference 49 Streamliner! You have a good method of getting it that clean as a home job? Just a bunch carb cleaner? 1 Link to comment Share on other sites More sharing options...
49 Streamliner Posted April 5, 2023 Share Posted April 5, 2023 I had the engine rebuilt last year at a local shop that specializes in old cars. He did the cleaning while everything was apart. The car was in the shop for about 2 months. The block and crank shaft were sent out to a machine shop. They were backed up quite a bit and it took about 3 weeks to get them back. He also did a fair amount of work besides the engine; brakes, clutch, new gas tank and fuel sending unit, etc. Replacing the tank was decided when the metal around the opening for the sending unit crumbled apart when he took it out. The sending unit itself was toast. Bill 2 Link to comment Share on other sites More sharing options...
mtl92 Posted April 5, 2023 Author Share Posted April 5, 2023 Yeah I would say that replacing was a good idea. I coated the inside of my tank last year. And resealed up seding unit. I have had issues though (before and after the coating) with fuel coming out of my filler neck when it warms up. Have you had this happen? I replaced the cap with one from chevs of the 40s but it still does it. Not sure if this is just a thing or not. Link to comment Share on other sites More sharing options...
49 Streamliner Posted April 5, 2023 Share Posted April 5, 2023 Here's a couple pages from the 1949-50 shop manual. The six and eight cylinder rear seals are different. Mine is an eight and has the setup in Figure 6-6. Your six cylinder is probably more like Figure 6-5. Bill 1 Link to comment Share on other sites More sharing options...
49 Streamliner Posted April 5, 2023 Share Posted April 5, 2023 The original plan was to clean the tank and have it sealed, but it had some weak spots that were almost rusted through. I haven't had a problem with gas coming out of the filler tube. The cap is a locking one that was on the original tank when I bought the car in 2004. It does allow some venting of fumes. It is probably not original to the car when it was new. 2 Link to comment Share on other sites More sharing options...
mtl92 Posted April 5, 2023 Author Share Posted April 5, 2023 Thanks for the pictures. I saw that California Pontiac Restoration has those wood wedges you talked about too. It might be a month or so for me to get to it but I appreciate your advice! Not sure what I'm going to do about the fuel yet. Link to comment Share on other sites More sharing options...
RussJagoau Posted April 10, 2023 Share Posted April 10, 2023 Having tried the Sneaky Pete tool on numerous occassions, just be forewarned that the rope type seals can get really tight in the recess that they sit in - especially over time. So much so that the tool can either part on you or it will just wedge the seal even tighter in the seal recess the harder you pull. So be prepared for a crankshaft removal task at worse or at least the slackening of the main bearing caps to allow a little more access and to relieve the compression on the rope seal itself. When the lower bearing cap is removed, suggest you see how much effort is required to try to remove the lower seal half. You can then ascertain the complexity of the seal removal task for the top half when the cranskaft is still in place...... WIsh you the best of luck...... 2 Link to comment Share on other sites More sharing options...
mtl92 Posted April 10, 2023 Author Share Posted April 10, 2023 Hey RussJagoau, Thanks for the tips! I'll definitely look the lower half over first. I'm sure they'll be plenty of expletives flying while I try this in a few months. Link to comment Share on other sites More sharing options...
mtl92 Posted June 26, 2023 Author Share Posted June 26, 2023 Well I thought I would give an update. I just finished the install and I ended up lowering the main bearing caps to the point that I could slide in the rope seal without the sneaky Pete. I couldn't keep the sneaky Pete on the rope as I pulled it so minght have been using it wrong but it's in now. I think though that the original seals themselves were probably fine but the wood blocks were most likely my source of leakage. Anyway, now to pull the trans apart to replace those seals. Thanks again for all the help! 1 1 Link to comment Share on other sites More sharing options...
RussJagoau Posted June 30, 2023 Share Posted June 30, 2023 Good job there. Whatever works to get the successfull outcome is the name of the game. 🛠️ Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now