Need Help with 1968 L 36 Rear Main Seal

[Richard T.]

I bought a pretty nice low mile (37,700) 1968 with the L-36 motor. I decided to drop the pan and change the rear main seal, timing cover seal, etc. My problem is the rear main seal will not budge at all. The lower half came out but it wasn't easy. It was brittle and hard. Any ideas for getting the top half out? I really don't want to pull the motor to do it. Rich

[Edward J.]

Re: Need Help with 1968 L 36 Rear Main Seal

Rich the upper half of the seal can be removed if you look closely at the other half of seal you removed you'll note that it has a thick heavy wire running around the seal if you can find something small in diameter to tap the bottom of the seal on the wire part just to start it, you can rotate the crank and pull on the other half of the seal. There is a special tool that has a shaft made of aluminum with a plastic handle that is used to aid with the starting of seal removal. just be extra careful not to damage or hit the journal of crank.

[Jim D.]

Re: Need Help with 1968 L 36 Rear Main Seal

I've done several, both in the car and on engine stands. All but one when smoothly. I had the engine on a stand and the seal was rock hard/brittle as you state yours is. The half in the main cap shattered into many pieces in order to remove it. The half in the block wouldn't budge when I tried to tap it out. I ended up having to remove the crank to get it out. It too was rock hard and had bonded securely to the block. Not trying to scare you but sometimes a 10 min. job turns into an all day fight. Good luck.

[Joe L.]

Re: Need Help with 1968 L 36 Rear Main Seal

I bought a pretty nice low mile (37,700) 1968 with the L-36 motor. I decided to drop the pan and change the rear main seal, timing cover seal, etc. My problem is the rear main seal will not budge at all. The lower half came out but it wasn't easy. It was brittle and hard. Any ideas for getting the top half out? I really don't want to pull the motor to do it. Rich

Richard-------


Here's the problem: the original rear main seals used for Chevrolet V-8's were made of neoprene. For 1968 big blocks, this seal was GM #3893298. Neoprene is only temperature resistant to a little over 200 degrees F. So, it's right on the edge of normal engine operating temperature, especially for a big block and especially for a 1968 with 195 degree thermostat. If, for whatever reason, the engine operates at a higher temperature for a significant period of time, degradation of the seal can be expected. Maybe even if they operate at normal temperature.

The modern seals, in use for at least the last 20 years, are made of Viton, a fluroelastomer. These seals are temperature resistant to over 400 degrees. The last available GM seal of this material for a Mark IV big block was GM # 10117767 but it's discontinued. No problem. Fel-Pro #2918 is exactly the same seal and easily available. I've even gotten a couple of these that had the 10117767 part number on them which was likely a packaging mistake.

[Richard T.]

Re: Need Help with 1968 L 36 Rear Main Seal

Got it ! Thanks to all who replied. Can't believe how tough it was.