I've got a 65' 429 with a rear main oil leak that I'm at a loss with. I've replaced this seal 5 times now. I'm doing a few different things each time with no luck. The leak is really BAD and I have 100% isolated it to the main seal. All of my top end possibilities have either been fixed or confirmed to not be leaking (oil sender, valve covers, valley pan, head gaskets ect). I have also verified the cam plug, oil galley plugs, and pan gasket are not the source. I'm using a single lip BEST seal (which I think is crap, but is only option I've found), I've tried clocking it with and without RTV, leaving it flush with and without RTV and no luck. I have it facing the correct way according to the manual (lip facing the front of the engine). I'm at a loss. I pulled the dizzy and am running the pump with a drill, put dye in the block to verify the leak, and it's for sure the rear main seal. Next options I see are converting to a rope seal or using a completely different application seal, but you can't look up dimensions for seals and rope so I'm reaching out you guys for any help. Any help or advice appreciated. Thanks Chopperman
Read through this 429 rear main seal leaks (cadillaclasalleclub.org) It's from 2012 but may have the info you are looking for. Cadillac parts Ltd (just the name sounds expensive) shows a seal that is allegedly reengineered 1963, 1964, 1965, 1966, 1967 Cadillac Neoprene Rear Main Seal (cadillacpartsltd.com) Not cheap though .
Make sure the crankcase is venting properly. Make sure the PCV valve is correct for the application and replace any soft or suspicious looking vent hoses. Check to see if the c/case vent filter is plugged. Are you possibly missing some sort of an oil slinger at the back of the crank?
I've read that thread a dozen times now LOL and that seal you have listed is the seal I've been using.
Rebuilt motor, PCV is hooked up and working right. I also switched my oil fill cap out to a breather style. I thought it might be crankcase pressure too, thats I pulled the dizzy and pressurized the oil system using a drill. No oil slinger. I need a Caddy GURU.
Reading the article @Mr48chev posted, these engines are problematic with that seal. have you replaced any parts other then the seal? Seems this engine had some issues back there. is the crank nicked or grooved ? Engine block ? It does not take much for oil to find a path out. I’ve seen a lot of guys get over zealous yanking seals and scraping or scoring the sealing area. I don’t use rtv I’ll put locktite flange sealant on the outside of a lip seal if I think the sealing area has been compromised. I have used in the past an diagnostic smoke machine ( used to find vacuum leaks and fuel evaporate emission system leaks ) to find pesky oil leaks. It might not be the seal at all but something “ closely related “
How is the surface the lip seal is riding on? If that’s worn down, the seal may not actually seal there. I don’t know this engine, could the sealing surface be sleeved? Sent from my iPad using The H.A.M.B. mobile app
crank looks great - no groove, I'm going to put some calipers on it though. Maybe someone turned it down at soem point or tried to "clean it up" I might need to jerk the trans out just to get a better look at the seal area and run the pump with dye again
Ok so is it just me or does it look like this seal is made backwards. I know it’s facing the right direction, but if you look at the grooves they don’t look right at all. I’ve seen stranger things happen.
I clicked around and came across this, it sounded interesting. Perhaps you've already seen this. "You haven't given us much of the history of this car. First , are you sure it is a 66 engine. The 64-early 65 ,427's had problems with these leaks. At engine #123045 (Serviceman feb 1965)they changed the rear main bearing and seemed to solve the problem. You mention the shoehorn tool. It was primarly used to keep the center (back bone, see Serviceman July1964) part of the LOWER seal in tack . Back to the cars history. Assuming it is a 1966, was the rear main bearing ever changed? When the change was made in 1965 ,it was a small change. There was an extra oil groove added on the rear edge of the bearing to channel oil back to the pan and away from the seal. The cap was changed so there was a connecting groove and the oil dumped in the pan. The Serviceman Feb 1965, tells how to file 63-65 caps so the new bearing can be used on the earlier models. In fact Cadillac dropped supplying the early type ,so you had to make the change. The problem is the older bearing will fit in the newer models and will cause leaks like you have .Warren" Its here. http://forums.cadillaclasalleclub.org/index.php?topic=120265.0 Sent from my SM-G973U using The H.A.M.B. mobile app
I saw that thread but couldn’t find any images to show the differences. I have a set of 65 and 66 caps and they’re both the same.
That seal in the picture looks like it barely touches the crank. Shouldn't both lips on the seal touch the crank?
Just for the sake of suggesting something . I have the motor out of my car to repair what I thought was a rear main seal. Turned out to be a rear pan gasket seal not thick enough to contact the pan lip and it had a real bad leak. You could jack up the front of the car enough to get the oil level high enough to reach the pan lip and it would drip out the back. Just a suggestion. Both of the Big Caddy motors I have built I used a rope seal with no issues. I read about the issues with rear main leaks and after doing a lot of cars with rope seals. that's what I went with.
I had the same problem on a customer's car that I put a 429 Cadillac in. It was apparently built by H&H Motors and they put the best seal rear main in it and It leaked everywhere so I put two more of those in it and it still leaked everywhere. The crank looked okay and the customer took it and he put another seal in it and it still leaks. Didn't know about the changing bearings and caps that might be good to know. I might pass that along to the customer as his motor was a 64 I believe
You didn't swap any main bearing caps around without having the block align bored, did you? The seal surface on your crank looks pretty gnarly, but I'm guessing there's no such thing as a "speedi-sleeve" to repair it. But hopefully someone can prove me wrong.
I haven’t swapped anything out, just verified they were the same. The crank is actually primo, it just looks like shit in the pic because of the assembly lube. the lip surface is tight. I honestly think this thing is made wrong. I’d like to get my hands on. NOS seal to compare.
So I finally got it to seal up. The last seal I got from Best was different. It was made from a MUCH softer material. When I called them to point this out, they swear they didn’t make a change but that doesn’t mean they didn’t have some quality issues. I went through 6 seal sets before getting the “soft” one. also, I didn’t use any RTV and installed the seal flush with the block. Sealed the main and joint with a dab of permatex red anaerobic gasket maker.
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