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Thread: Rear Main Seal Replacement

  1. #1
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    Default Rear Main Seal Replacement

    Well, on my 1983 C20 6.2 I seem to have developed a substantial rear main seal leak, oil pan gasket leak, or both.

    It's a two piece rear main and seems like I should be able to do it without moving the transmission or jacking up the engine.

    Just remove the inspection cover and maybe the starter, drop the oil pan, remove the oil pump and rear main cap, and so forth.

    Sound about right? Any pitfalls I should be aware of?

    I tried to search the topic in this forum but it returned a few thousand results.

    Any advice would be appreciated.

    Thanks
    1983 Chevrolet C20

    1923ish Ford Model T Touring

    2000 Lincoln Town Car

  2. #2
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    Just about right.

    Same basic thing you would do on an early RAT OR MOUSE MOTOR...

    If YOU ARE LUCKY and the engine has a hard backed neoprene seal it's pretty easy to shove the old one out and the new one in.

    If you find the rope type seal it can be a bit more work...


    Good luck

    JUST AN FYI

    These engines use a high temp silicone goop on the pan rails, so do not be shocked if you do not find a gasket...

    Gaskets were not used on these engine on the pan and rocker covers... only the goop.
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  3. #3
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    Default

    Hey thanks!

    So is it a good idea to use a gasket now, or just load it up with the high temp silicone?
    1983 Chevrolet C20

    1923ish Ford Model T Touring

    2000 Lincoln Town Car

  4. #4
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    Quote Originally Posted by sdelaney View Post
    Hey thanks!

    So is it a good idea to use a gasket now, or just load it up with the high temp silicone?
    NO gaskets. They'll just leak, sooner or later. Use "The Right Stuff" on clean surfaces and be done with it.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  5. #5
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    "THE RIGHT STUFF" IS GREAT....A bit more $$$ than the standard hi temp black silicone.

    The key to making any of the "GOO IN A TUBE" work well is to be sure that all surfaces are clean and OIL FREE...

    Use a clean shop towel and wet it with BRAKEKLEEN...Wipe all surfaces and allow to dry...then apply the goop.
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  6. #6
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    Default

    Thanks for all the info and advice. For now I'll file it away for later use.

    After contorting myself up under and on top I discovered that the leak was in fact coming from a pipe nipple that the PO used to install an after market oil pressure gauge (about 30 years ago based on the appearance of the gauge). The nipple had completely rusted through.

    An 89 cent brass plug solved that problem. Whew!

    Thanks again!
    1983 Chevrolet C20

    1923ish Ford Model T Touring

    2000 Lincoln Town Car

  7. #7
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    Gawd that's great news

    Doing a rear main seal from the bottom up is a sucky job unless you have it on a lift
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  8. #8
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    It's a sucky job if you have it on a lift. It's just more sucky if you don't. Great news, indeed.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  9. #9
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    At least on a lift you can get to everything and not have to crawl around on a creeper...or worse yet.............IN THE DIRT

    The last rear main I had to do I said noooooooooooooo waaaaaay to the bottom up and yanked the engine out, steam cleaned it well and then went after the beast.

    Discovered a weeping freeze plug under one motor mount (Sooooo...that was where the coolant had been going)

    Installed a fresh set of freeze plugs and the new rear main seal.....in fact if memory serves me we rolled in new bearings while the bottom was off and dropped in a fresh oil pump too.

    The timing cover seal was not stellar so ripped it off and stuffed in a fresh seal and a fresh chain while the cover was off.

    The valve covers were a bit oily so removed the fuel injector lines and resealed the covers.

    While it was right there it got a fresh set of glow plugs and took the injectors in for a refresh.

    Just about everything that is nasty to work on in the chassis was given attention.

    Thought about doing head gaskets but the engine did not have all that many miles...maybe 100K at the time.

    Ahh well...that truck lasted us 300K miles 1986 K2500 Burb 4x4
    Bought it with 30K on it from a dentist who's missus hated the diesel noise. Truck was like new when we got it.

    Real good deal that you did not have to dig into your rig very far....That's always a plus...
    Last edited by Robyn; 10-29-2019 at 05:26.
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  10. #10
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    Quote Originally Posted by Robyn View Post
    At least on a lift you can get to everything and not have to crawl around on a creeper...or worse yet.............IN THE DIRT

    The last rear main I had to do I said noooooooooooooo waaaaaay to the bottom up and yanked the engine out, steam cleaned it well and then went after the beast.

    Discovered a weeping freeze plug under one motor mount (Sooooo...that was where the coolant had been going)

    Installed a fresh set of freeze plugs and the new rear main seal.....in fact if memory serves me we rolled in new bearings while the bottom was off and dropped in a fresh oil pump too.

    The timing cover seal was not stellar so ripped it off and stuffed in a fresh seal and a fresh chain while the cover was off.

    The valve covers were a bit oily so removed the fuel injector lines and resealed the covers.

    While it was right there it got a fresh set of glow plugs and took the injectors in for a refresh.

    Just about everything that is nasty to work on in the chassis was given attention.

    Thought about doing head gaskets but the engine did not have all that many miles...maybe 100K at the time.

    Ahh well...that truck lasted us 300K miles 1986 K2500 Burb 4x4
    Bought it with 30K on it from a dentist who's missus hated the diesel noise. Truck was like new when we got it.

    Real good deal that you did not have to dig into your rig very far....That's always a plus...
    Lol,

    "While we're in here we might as well . . . "

    I had a 1971 Triumph Spitfire that went from chasing down a flickering headlight to a complete rewiring of the entire car, redesign of the dash and dash pad, modern gauges and switches, all because I removed the dash panels and had to remove some gauges (which is a bit of a production) to chase down the defective headlight wire.

    "Since I'm in here already anyway . . . "
    1983 Chevrolet C20

    1923ish Ford Model T Touring

    2000 Lincoln Town Car

  11. #11
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    Quote Originally Posted by sdelaney View Post
    I had a 1971 Triumph Spitfire that went from chasing down a flickering headlight to a complete rewiring of the entire car...
    That was the right thing to do. Or call the exorcist! Lucas, Prince of Darkness.

    My Austin Healey had 2 fuses, a 25 and a 50. Headlights didn't work in the rain.
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
    New ride: MB GLS450 - most stately
    Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510

  12. #12
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    Quote Originally Posted by JohnC View Post
    That was the right thing to do. Or call the exorcist! Lucas, Prince of Darkness.

    My Austin Healey had 2 fuses, a 25 and a 50. Headlights didn't work in the rain.
    Yep.

    I've seen sturdier wiring on a television remote control. I couldn't believe someone deliberately designed the wiring that way. I was convinced the engineers were drunk and had a contest to create the most inconvenient and impractical wiring possible.
    1983 Chevrolet C20

    1923ish Ford Model T Touring

    2000 Lincoln Town Car

  13. #13
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    Quote Originally Posted by sdelaney View Post
    Lol,

    "While we're in here we might as well . . . "
    Definitely have to watch those "might as wells!" I pulled a 6.2L out once to replace a collapsed lifter (hard to replace with the engine in the truck). I thought I would "freshen" it while it was out. That one collapsed lifter turned into a complete rebuild including boring it .040 over, custom ceramic-coated lower-compression pistons, timing gear drive, stud girdle, new injectors, injection pump, etc. I was astounded how each decision led to another, all because of "I might as well..."

    Casey
    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

  14. #14
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    Yup

    While we are here

    Much easier to get a good job with the engine out
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  15. #15
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    Quote Originally Posted by Robyn View Post
    Yup

    While we are here

    Much easier to get a good job with the engine out

    The moral of the story is "never take the engine out..."
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
    New ride: MB GLS450 - most stately
    Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510

  16. #16
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    Quote Originally Posted by JohnC View Post
    The moral of the story is "never take the engine out..."
    We have a list of rules for working onair-cooled Volkswagens. The first two items:
    • Pull the engine
    • Fix the brakes


    Seems to be the case for everything that comes in.

    To be fair, pulling the engine is disconnecting fuel, coil, alt/gen, throttle cable, oil pressure sender, four bolts/nuts, and then dropping it with a jack - a bit more if you're working on a bus. So it's easier to drop the engine to work on it.
    '94 GMC 6.5TD K1500 4L80E 2-Door Yukon SLE 221K
    '93 Chevrolet 6.5TD K2500HD NV4500 Std. Cab Longbed 187K
    '85 Toyota 22R RN60 4x4 Std. Cab Shortbed 178K (Currently retired for rebuild)
    Diesel Page Member #2423

  17. #17
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    Getting the engine out of the GM trucks is not all that hard.

    The resultant ease of doing the pan, rear seal and other things while in there is well worth it...

    Not to mention the color of the air surrounding the truck
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  18. #18
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