Is the rear main seal in a 1990 GMC Jimmy with the 5,7L a one piece or a two piece seal? Mine is leaking!
CK5
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rear main seal
- Thread starter TheRealJimmy
- Start date
As long as the engine hasn’t been swapped out it should be a one piece.
Does the engine need to be pulled to replace it?
Yes, or back out trans. No way around it.
Make sure it's not the back of the valve covers leaking. A lot easier fix and pretty common leak.
Also check the intake and dist gaskets. If the oil filter is not tight tight it will look like a rear main too
The oil pressure sensor is back there too
Seems to be leaking right at the back of the motor. 
dont know when that was cleaned last, but that sure looks like a leaking oil pan gasket in that photo - not necessarily the rear main seal. from experience with my last few 5.7 liter engines:
-rear main leaking will have oil slinging around coming off the engine side of your flexplate / flywheel
-rear of oil pan gasket leaking will be mostly on the back of the oil pan causing it to collect and drip off the oil pan when sitting
the last time mine leaked from rear of oil pan, I was affraid of making things worse after an all day pull, clean, degrease, wait for oil to stop dripping, clean again, try to assemble new pan gasket, and clean again and again type session?
I figured that the pan gasket is not seeing any pressure behind it, so i sprayed the garden hose up there, brake parts cleaner, compressed air, wiped, more brake parts cleaner... and just goobered some of the grey 90 min rtv into the gap -worked it in with a ruler and made sure it extended over the pan and the main seal retainer... all the way from corner to corner. not prettiest thing to do, but i was reasonably sure I would be the one pulling the motor for the next rebuild (yup I was). that grey rtv sets up really firm. No more grime and ooze from that particular oil pan gasket, but was kind of a PITA to get it all cleaned off a few years later. if the pan had been leaking from anywhere else, would have been worth the time to pull it off and replace it. They claim you can reuse the nice silicone pan gaskets with the compression inserts? ive reused the silicone valve cover gaskets, but to date have always still replaced the oil pan gasket -if it comes off, I dont want to do it twice, and make sure the entire area is clean , dry and oil free before putting the new one on.
i splooged everything as in the green area and even with the 90 min rtv, I let it cure 24 hours.
note about the main seals though - the factory cast iron cranks? I think the iron must be on the softer side of the spectrum. Ive worn a groove into seal surface of every one that I have run and used for any length of time. When the main seals started weeping, replacements would only last a matter of weeks. if not willing to pull the motor and rebuild, I highly suggest you find the correct "ready sleeve" or "speedy sleeve" before attempting to replace the main seal -that's my opinion for both the front and rear. last time i did it with motor in the K5:
rear- had to have the transmission out of the way. driveshafts off, shifter out, trans on transmission jack, crossmember off, and then lowered and pushed the trans/transfer case out of the way. flywheel off, and then had some room to get the speedi sleeve on the crank, and the new main seal in the retainer. pretty sure I had a cherry picker over the front of the motor supporting the weight when the trans pulled out - it was still tight under there trying to install that sleeve nicely and get the new seal installed straight.
for the front- the sleeve goes on the the harmonic balancer. i was worried about engine balance and installed a sleeve over the groove on mine, but later had to replace the balancer entirely for other reasons. For the front of my tbi engine or a stock vortec 5.7, I would probably avoid the sleeve from now on and just get a good quality new replacement balancer to install with the new main seal.
rear- had to have the transmission out of the way. driveshafts off, shifter out, trans on transmission jack, crossmember off, and then lowered and pushed the trans/transfer case out of the way. flywheel off, and then had some room to get the speedi sleeve on the crank, and the new main seal in the retainer. pretty sure I had a cherry picker over the front of the motor supporting the weight when the trans pulled out - it was still tight under there trying to install that sleeve nicely and get the new seal installed straight.
for the front- the sleeve goes on the the harmonic balancer. i was worried about engine balance and installed a sleeve over the groove on mine, but later had to replace the balancer entirely for other reasons. For the front of my tbi engine or a stock vortec 5.7, I would probably avoid the sleeve from now on and just get a good quality new replacement balancer to install with the new main seal.
Leave it alone and just add oil as needed. The flywheel covers had a hole for a reason.
That hole is where it was leaking from. I pulled it out to inspect it better.
Me, id leave it alone and just put cardboard under the vehicle. Adding small
amounts of oil every so often is far easier.
amounts of oil every so often is far easier.
meh. if its the rear of the oil pan, my vote is to gently snug up all the pan bolts, and then clean and degrease the heck out of that area, and try to work some of that grey RTV into the gaps and over all the edges of pan/block/seal retainer where they come together right there.
Mine leaked there and what I did was, brake clean the shiz out of the area, then applied some "right stuff" rtv. Worked good enough and yes, I gave the bolts a turn. Don't go crazy on oil pan bolts they have low torque spec from what I remember.
yup. they are tiny... at least the ones that don't have a stud. -1/4x20??
I hate leaks, I'd do whatever it takes to solve it. Sorry, I don't like worrying about having to add fluids. I have to remember enough other stuff. Especially with a one piece rear main. They shouldn't leak, they are a far superior design. If it's the pan gasket, replace it.
It's not that tough to pull the pan even in the vehicle is it? I haven't done it, but it will be something that I will have to do in the future. I can't recall anything being in the way really...
It's not that tough to pull the pan even in the vehicle is it? I haven't done it, but it will be something that I will have to do in the future. I can't recall anything being in the way really...
wouldnt want to on an ifs truck. on a solid axle with a lift it is possible... problem is trying to assure a dry clean surface for the new pan gasket. when you have an big 8 cylinder engine dripping oil from every square inch above the place you are trying to clean and dry???? not so bueno.
also while I like the one piece rear main design better than the old 2 piece, the grooves getting worn into the seal surfaces do happen, and unless you fix or replace the seal surface, you can keep replacing that superior design over and over and over again, but they don't seem to last very long!
I didn't realize this until I saw it in print one day, and while my experience is maybe 10 among millions, any double lip seal surface I've ever dealt with was on the dust side of the seal, not the oil side. I still speedi-sleeve them, but that was before I realized I was never seeing two grooves.
The picture shown is a solid front axle truck, so IFS isn't a factor, nor is vertical clearance. IF there is nothing to keep the pan from dropping straight down, there is plenty of clearance to drop the pan on a squarebody 4WD. Looks to me like it's super easy:
Not to get into a pissing contest, but every Chev small block installed factory since 1987(?) until the end of production used a one piece rear main. I find it exceptionally hard to believe those are more problematic than the two piece seals in service. My only "personal" experience with them were my buddies 1990 Suburban and my other buddies 1995 3/4 ton both with 100K+ on the odometers. Neither leak a drop from the rear main. I've only had my L31 crate in for about five years, and it rarely gets driven, so I'd not use it as an example of long term success.
The picture shown is a solid front axle truck, so IFS isn't a factor, nor is vertical clearance. IF there is nothing to keep the pan from dropping straight down, there is plenty of clearance to drop the pan on a squarebody 4WD. Looks to me like it's super easy:
Not to get into a pissing contest, but every Chev small block installed factory since 1987(?) until the end of production used a one piece rear main. I find it exceptionally hard to believe those are more problematic than the two piece seals in service. My only "personal" experience with them were my buddies 1990 Suburban and my other buddies 1995 3/4 ton both with 100K+ on the odometers. Neither leak a drop from the rear main. I've only had my L31 crate in for about five years, and it rarely gets driven, so I'd not use it as an example of long term success.
