1968 300 Rear Main Seal Leak

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mgm1986

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Fellow enthusiasts, looking for input from those who have done it before. I have been driving my 300 for probably a hundred or so miles now, just local back road running. I am very happy how well it runs and very surprised how much gas it burns cause I can't stay out of the secondaries!

What I don't love is the rear main seal is leaking. I can confirm it is not the oil pressure switch or the valve covers which leads me to the rear main seal. I have seen a few videos, read through the FSM and crawled under the car to inspect. I am not looking forward to this task but I also hate leaving oil everywhere I park. Although the undercarriage is mostly rust free being so coated in oil.

Remove the steering linkage to get the oil pan off (half the pan bolts aren't even screwed all the way), remove the two bolts holding the cap on and work out the old seal and replace with new.

Is it feasible to do this job without a lift laying under the car or am I going to need better access to do it the right way?

440BB, no idea if it's original to the car. Thanks in advance for your sage advice!
 
I know people who have rebuilt their engines lying on their back in February. Could I do it? Absolutely no way. For me the engine needs to be out of the car or up on the lift.
I suggest unbolting the engine mounts, raise the engine and pulling the entire pan off. I don't see the need to touch the steering gear at all.
After all is said and done, it might still leak, lol.
 
I have replaced the rear main seal in our 65 Ranchero. It wasn’t too bad. I botched the first seal, so I had to replace it and ended up boogering the oil pan gasket on removing it, so I had to replace that too. Nonetheless, with patience and attention to detail, I am confident that you can do this.
 
It seems like one of those jobs that is only difficult because you have to remove so much other stuff. And if it leaks you're pulling the oil pan off again.

I'll plan on getting it as high off the ground as I can and take a crack at it.

Thanks for the motivation
 
commando1 said:
I know people who have rebuilt their engines lying on their back in February. Could I do it? Absolutely no way. For me the engine needs to be out of the car or up on the lift.
I suggest unbolting the engine mounts, raise the engine and pulling the entire pan off. I don't see the need to touch the steering gear at all.
After all is said and done, it might still leak, lol.
Click to expand...

I will definitely remove the entire pan but I'm thinking the steering linkage is gonna need to get taken apart to get the pan off. If I could jack the engine high enough to get the pan off that would be awesome but I just did the motor mounts and it didn't look like an option.
 
You might check the Chrysler factory service manual to see about removing the oil pan "in car". Seems like there is something about manually turning the engine to get crankshaft counterweights out of the way?

Work safely!
CBODY67
 
My advice is to drive it some more and keep track of the leak amount. My 383 will leak a tiny bit (2-3 small drops) after a winter slumber then stop completely.. Seeing you have only driven 100 miles, maybe give it a little more time/mileage to see what you are up against. I've seen too many people go nuts replacing rear main seals and then... drip drip.. (as commando said above). You might get lucky but.. are you feeling lucky?

Good luck..
 
Finally decided to tackle the rear main seal leak. I removed the steering linkage and was able to lift the engine a couple inches to remove the oil pan.

After removing the rear main seal retainer I found the bolts used were too long which cracked the retainer on both sides. Now I am trying to figure out how to remove the old rope seal from the engine. Doing some research it seems I may need to loosen some of the caps to lower the crank but I am going to ask here before I start loosening those bolts.

I have tried to tap it through with a dowel. I also tried using a screw to pull it out (like a corkscrew). My next thought seemed dangerous to try; set the thing on fire and let it burn itself out!

Any suggestions or wisdom on removing an old rope seal while the engine is still in the car?
 
Dang, guess my google search skills need work! I ordered the sneaky pete, will be here in a couple of weeks. Will report back with my results. Cleaning it all up once the seal is out will be another fun challenge!
 
Unfortunately the Sneaky Pete did not work to remove the upper half of the rear main seal (it is a rope seal). It would only screw in about half way before seemingly bottoming out. I removed the rear crank cap to improve access but still unable to get the old seal out.

I am now planning to remove the engine and transmission to finish the job. I half everything except the drive shaft and exhaust manifolds disconnected. Once those are apart it looks like it will slide out fairly easily.

With the engine out I am going to give the engine bay a good clean, re-gasket the engine and give it a coat of paint. My first engine removal so hopefully it goes back together as easy as it comes apart!
 
mgm1986 said:
Unfortunately the Sneaky Pete did not work to remove the upper half of the rear main seal (it is a rope seal). It would only screw in about half way before seemingly bottoming out. I removed the rear crank cap to improve access but still unable to get the old seal out.

I am now planning to remove the engine and transmission to finish the job. I half everything except the drive shaft and exhaust manifolds disconnected. Once those are apart it looks like it will slide out fairly easily.

With the engine out I am going to give the engine bay a good clean, re-gasket the engine and give it a coat of paint. My first engine removal so hopefully it goes back together as easy as it comes apart!
Click to expand...
Sorry to hear about that. You’ll get there.
 
I’d replace the rope seal with another rope seal. I can almost guarantee a lip seal will leak as much or worse…
 
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Finally had time this morning to pull the engine. I did not remove the transmission cross member but I should have and will before dropping it back in. With a little luck I'll have everything cleaned up and the front suspension rebuilt before spring.
 
Pulling the 440 apart, taking my time best I can.

It appears to be a 1973 block, stamped J 440 T and the casting says 73 albeit very hard to read. It has a forged crank with "six pack" rods (#2951908) although I've read that's not necessarily a pro or con, just making note of it.

It has 213 heads on both sides. I pulled, cleaned and lapped the valves and replaced the valve seals. Hopefully I didn't futz anything up cause it was running nice before. Would hate to have to get new heads and free up some torque and HP :p

The log style manifolds are badly pitted and frankly I just wanted to try headers so I went with Hedman mid length headers. I did need to grind down a small chunk of the block to get them to sit flush on the head (circled red in picture). Outside of that they fit nicely and access to spark plugs was fine. How they fit in the car is TBD.

Hedman Hedders 78070 Hedman Street Headers | Summit Racing

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Had two nice days of warm weather so I turned my attention to painting the block. Learned a lot.

I brushed on POR-15 Gray as the first coat and their Chrysler Turquoise as the top coat. It looks very nice. I had to sand the gray because I didn't have time/weather to get the top coat on before it cured. It could probably use a second coat in some spots, my lighting sucks in the garage.

After I get it back on the engine hoist I'll paint the back of the block before mating the transmission.

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20241231_152700.jpg
 
Finally got the motor back together enough to put oil in. I used a new 6 quart pan from 440source and the all-in-one windage tray gasket torqued to 100 inch pounds. Both very nice products.

I then primed the engine to make sure I was getting oil through the valve train on both sides (I swapped heads side to side); I was. To do this, I cut the head off a big 5 gallon paint stirrer I had as it fit perfectly in the oil pump. I made sure to wrap it with a good amount of electrical tape where it was going to ride in the bushing and it worked great.

I was able to rotate the engine while running the pump with the drill which was great because it helped me confirm that the new rear main seal was leaking. This was the orange two piece fel-pro seal that came with the new Hughes engine retainer. As @detmatt pointed out, I should have gone rope seal which I just ordered from Mancini.

What I did notice was the orange two piece seal wasn't actually sitting flush on the crank, even when trying to press it down.

The black fel-pro two piece seal that came with my engine gasket set actually seems to fit very nice and flush on the crank BUT, I am still concerned that a rubber seal isn't going to actually seal very well against the knurl on the crank. At least my brain tells me all those little knurls are just crevices for oil to seep through when the engine isn't running.

I will try again with the rope seal and report back.
 
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