Rear Main Seals

TimAT

Addict, Cruise-In Bird-Run 1 Veteran
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Mar 24, 2008
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Gladstone, Missouri
Not really a Mod, but info. Maybe need to move or post someplace else?
Kind of generic RMS instructions. same thing applies to SBC or BBC with 2 piece seals..

Once you have the pan down, remove the oil pump and pickup. Remove the rear main cap. The lower half of the seal is right there. Don't scratch the bearing. Take a small screwdriver and pop the lower half out of the cap, then use the screwdriver, (I have one that I did a little bit of grinding on so it's got a better flat end) and push on the exposed end of the upper half of the seal. You may hve to tap it a little bit to break the upper seal loose. Drive it out until you can get a good grip on it and then just walk it on out. Now the old seal is out, clean the block and the seal groove with something like brake cleaner, just hose it out really well.

The trick part is next. GM and the aftermarket have 3 different widths of rear seals. The difference in them is from the dust lip on the back to the wiper lip on the forward side of the seal. The best (and widest one) is the one you need to find. The biggest distance between the two lips. You may have to hunt for it. GM had them all under the same part number, but there are different ones.

For a SBC, take a look at Fel-pro BS 11829-1.


Take the rear main cap to your bench grinder and use the wire wheel on the mating surfaces adjacent to the seal. Don't get so far forward to catch the bearing. Buff the cap, get it really clean. Then hose it down with the brake cleaner too. Let it dry while you install the upper half of the seal.

In the package there is a little plastic "spoon". Use it to install BOTH the upper and lower halves. Put a little bit of grease on the lips of the upper seal. If you don't, the rib on the inside of the seal gets sliced off and will seep underneath the seal. I've seen lots of posts where guys say to offset the ends of the seal. If you decide you want to do that remember there's no way to install the cap without cutting the seal rib off the OD of the seal. I don't recommend it. GM spent big $$ developing the rubber seal.

rearmainseal1.jpg


Once you have the lower seal in place, wipe a little bit of grease on the lips of that seal too. Apply a very thin coat of form-a-gasket or an anerobic sealer or something like that on the cap next to the seal. Not on the seal, but in the shaded areas on this picture. Don't use RTV here- it's too thick and could migrate into the bearing or the drainback groove and cause other problems.

rearmainseal2.jpg


Install the cap, torque to specs and install the oil pump, and pan. I personally haven't used one, but from the feedback I've seen the Fel=Pro one piece pan gasket is the way to go.
 
Good info. I have ALWAYS off set the ends of the seal. Not one of them (MANY built) has leaked...............till now. My new engine has a rear main seal leak. :mad:


So when are you going to be here to change it for me?
smikey_tank_flags_gis.gif
 
Good info. I have ALWAYS off set the ends of the seal. Not one of them (MANY built) has leaked...............till now. My new engine has a rear main seal leak. :mad:


So when are you going to be here to change it for me?
smikey_tank_flags_gis.gif


Your L-82? :eek:I wouldn't be tooo worried about that one. Just get a bag of cat litter and throw a handful under the car when you stop. Or a box of diapers.
 
Your L-82? :eek:I wouldn't be tooo worried about that one. Just get a bag of cat litter and throw a handful under the car when you stop. Or a box of diapers.


DEPENDS on how much you leak, I suppose....:yahoo::shocking::p:beer:
 
TimAT,

It's been a long while since I replaced a two piece seal just droppin' the pan, but I do remember layin' under a couple cars and not being to get the top seal to budge. A friend showed me to take a flywheel turner, and while pushin' on one side with a screwdriver, turn the flywheel same direction slightly, and it'll damn near turn itself out. At least enought to grab. Just hopin' to help someone.
 
On a closely related matter, I ran across a mod I'm very likely to perform on my Mark IV BB that seems to make sense for SB's too; O-ring the oil passages in the block which mate with the rear main cap. I believe Gen 6 BB's come that way. Thoughts?
 
Not a really bad idea. The added time and expense might make it financially unworkable. Most leaks are really past the seal on the crank. If you apply sealant to the mating surfaces of the cap and block, and then make sure the pan is sealed up, (and fits correctly) it should be unnecessary.
 
just put a can of crap in the oil. it makes the rubber swell up and the leaks stop.

you'll probably total the car before it needs to be pulled apart and fixed.
 
Cat shit?:eek::eek:
:fishing::thumbs:


But seriously, I used a 500 Caddy rear main seal, two crescents with rubber lip seals to be pressed into the block/cap....all fine, it was put into a Pontiac 455, same size everything, but it leaked like hell, really reall reallly bad....

took me tons of effort, but I WON....found out the ends of the seals needed by gapped/ground down about 1/16th inch or so, did it right there on the grinding wheel....as when I finally layed them together on the bench, and miked the interiors, exteriors, I found the ends had to be mated, otherwise they just pushed their way into the block/cap, and did not seal around the crank.....3 attempts on that, drove me crazy....went through TWO seals for that shit, and so I bet ti's the same thing.....

I never did stagger that last install, but put a slight dap of RTV black on the ends, torqued it down the last time and it never leaked a drop for some 8 more years....

so lay them puppies out and mike hell outta them first before installing....

YMMV, obviosly....:sos::stirpot::smash::thumbs:
 
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