Small Block Chevy Rear Main Seal

Discussion in 'Shop - Engine' started by John_Bitting, Feb 3, 2009.

  1. John_Bitting

    John_Bitting Administrator

    Joined:
    Apr 10, 2001
    Location:
    Rancho Santa Margarita, Ca
    Since I got the blazer running, I noticed the rear main seal leaks. I am not very knowledgeable when it comes to this aspect of the motor. Is it a ton of work to change? Should it be leaking when the vehicle isnt even running. I cleaned up the floor and it has a puddle under it again in a week. Can a prep shop fix it? Should I take it to a mechanic shop? Any advice is appreciated.
  2. FABRICATOR

    FABRICATOR Well-Known Member

    Joined:
    Apr 3, 2001
    Location:
    Ventura County, CA
    Re: Small Block Chevy Main Seal

    If it leaks a lot while sitting it could be from the oil pan where it goes around the main seal. This requires R&R of the oil pan.

    Unless it is a very early SBC, it will have a 1 piece rear seal. That means either the engine or the transmission needs to come out to get to the seal. It's usually easier to remove the transmission. Just make double shure that is it dry on the back of the engine above the bell housing. If it's wet up there, the leak could be from the distributor or intake manifold, which is much easier to fix. Also make sure oil is not coming from immediately above the oil filter area.

    A trustworthy mechanic will thoroughly clean all the areas and verify where the oil is coming from before tearing into it.
  3. John F2000

    John F2000 Active Member

    Joined:
    Feb 21, 2006
    Location:
    El Cajon Ca
    Re: Small Block Chevy Main Seal

    if the puddle is not that big, ignore it. Mine leaks when its not running as well.
  4. jeff

    jeff Super Moderator

    Joined:
    Apr 1, 2001
    Location:
    California
    Re: Small Block Chevy Main Seal

    Hey Juan.... what was I saying about "just run it" ??? ;) If the leak is how I remember it the puddle was probably only an ounce or two every week. It was a big enough leak that a drip pan was required to contain it. It's more than a weep and not anywhere close to a gusher. I can't remember if it leaked once the engine was running or not.

    Aloha
  5. johnnyweb

    johnnyweb Well-Known Member

    Joined:
    Jan 24, 2003
    Location:
    Gilroy-Shop
    To change the rear main on a early generation sb Chevy you only have to drop the pan and rear main cap. The trans can stay in. It could also be the pan gasket. Do not use silicone.IMO A good quality one piece pan gasket is the way to go. Could be a leaking oil galley plug in the back? Did the pan get retorqued after a few miles? Some times people over tighten them and screw up the gasket as well. Most good quality gaskets have inserts to prevent over tightening. It's funny you ask about a prep shop or auto mechanic shop to fix. Any good prep shop should be way over qualified to handle a repair like this a good prep guy should have been there and done that when it comes to changing a pan gasket or main seal. Good luck with it! If all else fails invest in a good old quality drip pan!LOL
  6. Ryno

    Ryno Well-Known Member

    Joined:
    Sep 24, 2001
    Location:
    Yucaipa, CA
    To R&R the rear main, slide the trans back, or take it out. Less work to pull the trans than the motor. Get a new oil pan seal while you're at it. If you can find a rubber 1 piece, with the grommets, that's the way to go. If it's a small puddle, run it until it goes out. Too much work for a small drip leak.
  7. johnnyweb

    johnnyweb Well-Known Member

    Joined:
    Jan 24, 2003
    Location:
    Gilroy-Shop
    If it is early generation sb Chevy you do not have to remove the transmission to change the rear main seal on the engine!!!!!!!!
  8. John_Bitting

    John_Bitting Administrator

    Joined:
    Apr 10, 2001
    Location:
    Rancho Santa Margarita, Ca
    False alarm, main seal is bueno. Freeze plug above it tricklin some coolant. Put some stop leak in. Total relief.
  9. Ol' Curmudgeon

    Ol' Curmudgeon RDC's resident crackpot

    Joined:
    Dec 29, 2004
    Location:
    The Cloud
    John, if you can't tell ethylene glycol from motor oil, I recommend an ophthalmologist. ASAP!
  10. richcomstock

    richcomstock New Member

    Joined:
    Aug 24, 2003
    Location:
    CA
    Are you sure it's coolant? You better taste it.....and if you go blind then you were right=)
  11. partybarge_pilot

    partybarge_pilot Well-Known Member

    Joined:
    Feb 19, 2002
    Location:
    Leucadia, CA.
    Freeze plug or cam plug? The cam plug is directly above the main seal and it would be leaking oil not coolant........
  12. sean (yt)

    sean (yt) Member

    Joined:
    Apr 23, 2006
    Location:
    northridge, ca

Share This Page