LS1 Rear Main Seal leaking.

[lux]

1972 C10 with a LS1 and a 4L60e transmission, I believe the rear main seal and or the seal plate are leaking. Any advise on being sure this is the problem would be helpful.
Has anyone done this repair in the driveway/ garage? How difficult and any advise at all?
It only leaks about a half dollar size spot after driving. I've inspected the top of the engine well and my mechanic replaced the valve cover gaskets, but the problem is still there. The small amount of oil is alway on the back bottom of the engine and on the transmission, defiantly not transmission fluid. It could be the back of the oil pan but, I think it's more than that.

Thanks

[87chevy.com]

Honestly, if you took your truck to a mexhanic to get valve covers done on a 5.3 ls... you dont even need to worry abkut how difficult it is to swap rear main seals...
Just take it back to your mexhanic and have him do both

[crazy longhorn]

Just a couple more thoughts....the flywheel bolts go all through, on the crankshaft.If you do not use a red locktite, they can seep through the threads on the crankshaft. 2 nd thought (true ls-1, 5.7), has gun drilled mains, & requires a welch plug , in the back of the crankshaft to seal. From what I have seen, the truck engines are not this way....Longhorn

[lux]

Thanks Crazy Longhorn, That's what Ive become used to on this forum. A bunch of folks trying to help each other out.
Yes It is a LS1 5.7L out of a 2000 corvette. You can disregard what the 87chevy guy wrote I thinks he is confused. I don't know of a LS1 thats a 5.3L.

I'm not sure what a "Welch Plug" is? I'm going to google it next.
I'm sure I can drop the tranny no problem and remove the rear main seal plate. I can replace the seal just fine as well. I think my problem starts with the alignment of the seal and plate putting it back on. Some companies make a plastic alignment tool. Other folks on line say you just need to get it on with lose bolts then turn the shaft a few times to line it up. Then your fine to tighten to spec.
I've also read some people say don't remove the plate, then some people say you really need to replace that gasket too. I'm thinking I should replace both the seal and plate gasket.

Thanks for constructive replies in advance.

[72blu]

I had what I believed was a rear main seal leak on my LQ9 but after further investigating it ended up being a leak from one of the rear cover bolts. I did the job on a hoist so I cant really speak on the difficulty of doing it on your back. I know they also make a rear cover with the seal already in place and all you would have to do is slide it in place over the crank.
Heres the part on Amazon https://www.amazon.com/Dorman-635-51.../dp/B009ZBSBMO

[crazy longhorn]

Originally Posted by 72blu

I had what I believed was a rear main seal leak on my LQ9 but after further investigating it ended up being a leak from one of the rear cover bolts. I did the job on a hoist so I cant really speak on the difficulty of doing it on your back. I know they also make a rear cover with the seal already in place and all you would have to do is slide it in place over the crank.
Heres the part on Amazon https://www.amazon.com/Dorman-635-51.../dp/B009ZBSBMO

I did mine that way also....it was about as cheap as the seal & gasket + you got the cover & got new bolts longhorn

[lux]

Thanks for the help guys, I'm gonna dive into it when I get the time. What the hell I just might learn something.

[68c10airstream]

Originally Posted by lux

Thanks for the help guys, I'm gonna dive into it when I get the time. What the hell I just might learn something.

As a past dealer mechanic when we had oil leaks like a rear main and we wanted to get to the bottom of it we would add a specific dye additive in the oil and then run the engine for an hour or so for slight leaks, shorter times for bigger leaks and then remove the trans and once at the area of question we would use a special black light sort of light and the leak under this special light would "GLOW" and glow the brightest at the source of the leak. The additive is cheap and i don't think the light costs are bad. Tooltopia.com i believes stocks it. This would take all of the quess work out of it!
After removing a 700r4 out of a 80's vintage 2.8 v6 s10 blazer (not fun) to go for a rear main seal only to find a distributor base gasket leak i used the dye every time for oil leaks in bad areas!!

[izzy_Britton]

I have been having a similar issue with one of my trucks since the day i bought it a few months back. started like you say, leaving little quarter size drops, 2 of them. then progressively getting worse the more i drive it. now the entire underside of my truck is coated with oil and there is an outline of oil where i park.

where does it appear to be dripping from? mine started at the starter bolts, and after removing the starter while the truck was running i found that is does appear to be coming from the rear seal plate or one of the bolts or somewhere UP there. it is high enough that i cannot trace its exact location.

after someone vandalized my truck and broke into it and then purposely ran into it in my parking spot at home while i was sleeping, i now need to replace the radiator support, radiator, condenser, grille, lights, and hood. I just ordered all these parts from work today and figure i might just pull the engine to fix the leak while the entire front of my truck is blown apart. I do not relish the idea of fixing it on the ground on my back as you have mentioned.

please let me know more about your leak and if you get to your leak before i do i will be following along.

-Izzy

p.s. mine is 4x4 2500HD 6.0