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Rear Main Still Leaking -- Possible Theory ....

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Stoopalini, Apr 2, 2002.

  1. Stoopalini

    Stoopalini 1/2 ton status

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    I've replaced the rear main 3 times already, and everytime it develops a leak again. The leak takes a while (200 - 300 miles later?) to come back each time.

    Last time I was under there, I noticed that my flywheel is missing a few teeth ..... alright, it's missing quit a few teeth.

    Would missing teeth on the flywheel cause vibration in the crank and therefore a leak in my rear main seal? I know I need to replace the flywheel anyway, I just want to know if this would be the cause of my continuous leaky rear main.

    Thomas.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    I would think it's possible (slight off balance) but not likely. Did you check the crank for a groove? Apparently that can be a problem, just like the harmonic balancer.
     
  3. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    There are several things that could cause the rear main to continue to leak. The worst case is that the engine has lots of miles and the main bearings have too much clearance which allows the crankshaft to move around too much and create a leak. Second, the seal area of the crank might have a groove that is too deep for the seal to seal against, but not likely because you say it takes a couple hundred miles before it starts leaking again. Last, if you have a one piece rear main seal engine in your truck they are very critical about the amount of torque on the flexplate bolts. The bolts on these engines are on a 3" bolt circle which puts the bolts very close to the edge of the crank and over torqueing the bolts can cause the crank to raise up at the bolts and or crack the crank at that point causing it to leak.
     
  4. Stoopalini

    Stoopalini 1/2 ton status

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    Thanks for the ideas guys, here's a little more info on the engine.

    The engine is a 350 with aprox 60k miles on it, and has a two piece seal. It runs very smooth, meaning I don't hear any internal engine noise that would suggest bearing problems. I'm not saying there couldn't be a bearing problem, but if there is, it's not bad enough to be able to hear it yet.

    I didn't notice a groove on the crank, although I didn't specifically look for a groove when I changed the seal. I'll definitely look for it next time I change the seal.

    Thanks again guys,

    Thomas.
     
  5. René

    René 1/2 ton status

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    Actually there is nothing to add to the text of Scott. You can try to process the seal place of the crankshaft with quite fine emery(abrasive). Then you can hope only, that new seal will seals. By the way also Landrovers have the same, unsolvable problem.

    Your should cange the flexplate as fast as possible before to get a larger damage
     
  6. FWP

    FWP CRS

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    How are you putting the seals in? The installation is critical to a lasting sealing surface to be maintained. Most guys I know, including me, put the seals slightly offset in the cradle(1/2"), not lined up with the cap ends. If you use RTV on the ends of the seals, it must be very very thin. And of course all the seal mounting sufaces must be free of any oil (hard to clean up with the engine in the vehicle, but possible). Also, if the crank is groove free, you may want to take a little emery cloth to ONLY the seal surface area on the crank, and scratch it up a little to help the seal seat to the crank.
     
  7. ntaj*ep

    ntaj*ep 1/2 ton status

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    I have done a few main seals, one thing you did not menction was weather you were pulling the trans or motor to do this? I have about a 50/50 ratio of success when pulling the trans. and 100% success when pulling the motor, only with the 2 piece seals. The one piece seals are cake for some reason, like the new Rovers, simple with the trans. removed. My suggestion to you is replace the seal with, as someone alredy said the seal riding in a slightly outward position. I think your not seeing the leak resurface until a few hundred miles is because you clean all the oil around the seal and it has to accumulate in the bellhousing before leaking where you can see.

    The flywheel teeth can be flipped on the flywheel its self. If your starter is grinding. BTW, hope this info is useful to you.
     
  8. 84_Chevy_K10

    84_Chevy_K10 Banned

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    I agree. I cock mine in the "cradle" a bit too and I haven't had any problem.

    There's no reason to pull the motor or the trans on our trucks to replace a 2 piece RMS. Just drop the pan and go to town.
     
  9. Blazer1970

    Blazer1970 1/2 ton status

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    Is your PCV valve working properly? The PCV system provides a slight vacuum in the crankcase which helps keep all of the seals from leaking. The first seal that is going to leak when excessive crankcase pressure is present is the rear main.
     
  10. Stoopalini

    Stoopalini 1/2 ton status

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    When I replaced the seal, I did not line it up off-center; I lined it up flush with the cap. I didn't use any RTV, and I made sure the seal surfaces were clean of all oil. I used brake cleaner and a rag to completely clean the oil and dry it. Basically, I just did it exactly how the Chiltons described.

    All the other SBC engines I've owned, were one piece seals and I never had a problem after replacing them. I thought the two piece would be nicer, being that you can replace it with the tranni in the vehicle; but this leaking problem has me wishing it were a one piece!

    My PCV system seems to be working properly. The hose is not clogged, and if I remove the valve with the truck running, it is definitely pulling vaccuum.

    Thanks for all the suggestions guys, I'll give it a go again, and this time I will offset the seal about 1/2", check the crank for grooves, and use a small amount of RTV on the seal ends. Hopefully, these things combined will solve my problem.

    Thomas.
     
  11. 84_Chevy_K10

    84_Chevy_K10 Banned

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    I don't care for the 1 piece seals. They don't leak as often, but they're more work to fix when they do. I haven't had any problems with the 2 piece seal in my new motor though.

    If you line them up flush with the cap, they'll leak every time. You've also got to use some kind of gasket sealer on the cap. I use non-hardening sealer.
     
  12. dragricinMT

    dragricinMT 1/2 ton status

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    Next time you replace your seal get a relocator seal. It is offset so it rides in a different area of the crank. This way if the crank does have a groove this should solve your leak.
    NAPA sells the regular seal and the offset, or relocator seal.
    Solved my rear main leak.
     
  13. txbartman

    txbartman 1/2 ton status

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    With the engine in and the tranny installed, how would I tell if my rear main seal is leaking or if it is my rear oil pan gasket?
     
  14. shane74

    shane74 1/2 ton status

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    So I need to drop my tranny or pull my engine to replace the rear main if it's a one piece? I have a '74 and my rear main is leaking pretty bad. I think it's a one piece but I'm not sure. I think it is the original engine, but I don't know for sure. I need to fix it soon.
     
  15. Stoopalini

    Stoopalini 1/2 ton status

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    If you can't tell where the oil is coming from (RMS or Oil Pan), and you have a 2 piece rear main, I would suggest you just replace both and be done with it.

    If you have a one piece seal, the I would replace the oil pan gasket 1st, and it nogo, it must be the rear main.

    The only way to replace a one piece rear main, is to seperate the tranni from the engine.

    Thomas.
     
  16. shane74

    shane74 1/2 ton status

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    Ugh!! That's what I was afraid of /forums/images/icons/frown.gif.
     
  17. 84_Chevy_K10

    84_Chevy_K10 Banned

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    A stock '74 wouldn't have a 1 piece though. Only '86 and newer engines have them.
     
  18. shane74

    shane74 1/2 ton status

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    It looks like I have a project for this weekend.
     
  19. 84_Chevy_K10

    84_Chevy_K10 Banned

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    It shouldn't be too bad with a 2 piece.
     
  20. Stoopalini

    Stoopalini 1/2 ton status

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    The two piece is really easy, just messy.

    I can get mine done in about an hour (or an hour and a half + 3 beers /forums/images/icons/wink.gif) .... Of course, I've done it 3 times now! /forums/images/icons/shocked.gif

    Thomas.
     

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