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Rear Main Seal Replacement


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Torque Specs:

Bearing cap: 80 lbs/ft.

97+ Brace:  35 lbs/ft.

oil sump screws:  1/4" screws to 7 lbs/ft and the 5/16" screws to 11 lbs/ft

Tips from 5-90

1) Whatever year your rig, use the 1996-up sump gasket. It's one-piece moulded rubber, and that saves you fighting with the thing!

2) DO NOT OVERTIGHTEN the oil pan sump screws! (The small screws are 1/4"-20x1/2", the large ones are 5/16"-18x3/4")

3) You don't have to remove the transmission - the 242ci had a two-piece rear main for the entire production run. The rear main not, however, a "rope seal" - it's rubber moulded over a metal core. You can start the upper half out by using a short brass rod against the end and tapping with a hammer (use brass or bronze so you don't scuff or scratch the crankshaft.)

4) Before you take the first screw out, pour a cupful of clean engine oil and drop the new rear main in there to soak. Leave it in there until you're ready to put it in. This makes it easier to install, and the seal will pick up more quickly.

5) I've never put RTV on the ends of the seal - it protrudes slightly from the cap and block at both ends, when properly installed. Leaving it soaked in oil for all that time makes the rubber more pliant, and the seal will then seal against itself. I don't like putting anything on main caps - makes it entirely too easy to screw up bearing clearances.

6) Use LocTite #242 on the oil sump screws. Torque the 1/4" screws to 7 pound-feet, and the 5/16" screws to 11 pound-feet. The rear main cap gets torqued to 80 pound-feet.

7) You'll have to remove the starter to get it out of the way. Disconnect the negative battery cable, and the starter will probably take a 9/16" for one screw and a 15m/m socket for the other (one is 3/8", the other is 10m/m. No, I don't know why, either...)

Is your rig lifted? I was able to do a rear main on a rig with a 3" lift with all four paws on the ground (I actually had to re-crank it, but I had room to work.) If not, it can get dicey...

A) Jack the front end up and support by the frame rails until the axle gets to full droop. You should be able to see a bit of daylight (I prefer an inch or so) under each of the front tyres with the vehicle suspended by the frame rails.
B) If you need more room, use a 13m/m socket and remove the four nuts that hold the transmission mount to the crossmember. Jack the drivetrain assembly up by the transfer case. This gets you 3/4" or so at the bellhousing.