Help with one piece rear main seal

[blend5]

Good morning/afternoon, all.

Too long don't want to read: I would appreciate some help with step by step instructions replacing a one piece rear main seal on a 72 4x4 Blazer with a late 80's 350 and sm465 transmission.


I'm not a mechanic. I just started learning this stuff a month ago. So far I've replaced the timing cover and gasket, oil pan gasket, water pump, alternator, power steering pump, and valve cover gaskets. I still have a pretty good leak where the engine meets the transmission. It's coming down the crack of both sides and out the dust cover hole. Checked the distributor and oil sensor. All seems ok there. I think it's got to be the seal and I'm pretty sure I'll have to pull the transmission. I found a shop that will do it for 600.00. That's sounds like a great deal and money isn't an issue, but I would like to continue my learning process and try it out on my own.

Can I do it by myself if I had a transmission jack? Or would it require two people?

Thanks in advance for any help/input you may provide. Have a good one.

[geezer#99]

Never done a one piece myself but here's what I'd do first.
Clean off the back of the motor completely and then check for leaks. Could be coming from the intake to block gasket area.
You got any pics of this motor?

BTW, welcome to the jungle!!

[Bigdav160]

I'd check the china wall at the back of the intake manifold. A leak from there will show up like you've seen.

Rear main seals usually just run down the back of the oil pan.

[Marshy]

Check out YouTube for some examples. Just search 350 rear main seal replacement. Just make sure you are watching a video for the one piece seal and not 2 piece. It's straight forward but will have to decouple the Trans from the motor and take the converter or flywheel off the crank snout. I agree with the others though, make sure it's not a leak on the back of the intake manifold at the China wall. Another thing to consider, check your oil pressure sensor. They can leak a lot of oil if it's failed.

[storm9c1]

I agree with everyone else. Clean it off with brake cleaner and check the intake first. Also check/clean/replace your PCV valve. I had one clogged up so bad one time, it was pushing oil out of every seal in the engine... but especially the intake area and was dripping down the back.

Replacing a 1-piece seal can be quite a bit of work. If it's a slow leak, with automatics, I just ignore it until I get the trans rebuilt. Or with a manual, do it when you do the clutch.

[blend5]

Thanks, all. I will check the intake manifold. It's really hard to see anything back there. I guess I need to pull it off. The oil pressure has been on the high side so maybe that is contributing as well? I'll try and get some pics this weekend. The engine came out of a late 80's caprice. It's a 2 bolt main. Block says 638 and the stamp under the valve cover dates to 88 I believe. The guy i bought it from said it came from a 2000 caprice police car, but I've figured out that isn't correct. It also has an edelbrock carb and I think the engine was originally was fuel injected. When they made the switch, it may have not sealed up well enough.

[Marshy]

A good mechanics mirror will help a lot. Good luck.

[cg285]

china wall? you guys have some colorful vocabulary

[71meangreenc10]

If your not a mechanic, this may be a job you do not want to tackle. It helps to have the experience when putting the clutch back in so you are not having to take it back apart if it is installed incorrectly.

Rear main on a 4x4 is always a pain. Multiple ways to do it, but still a pain. If you do have a one piece rear main, that helps because you dont need to remove the oil pan. But, you still got to get to the main. A good trans jack will help, but you may need help getting the trans/transfer to move where you want to.

If you think you can do it, go for it. Youtube it to death, make sure you have the ability to realign the clutch disk to the flywheel so it mates to the trans.

Smitty