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Hello, My name is Morey and I own a 1968 Cornet RT 440 Magnum. Looking forward to exchanging info with the experts and referencing the forum. I'm currently planning to replace the rear seal and looking for advice what seal to use and tips to help with the process.
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Hello Morey!! Rear seals while the engine is still in the car are certainly more difficult. Many good mechanics have ripped the pan and tranny out to replace the rear seal only to find it's coming from another location. The valve cover gaskets leaking follow the same path down the back of the engine dripping off the bellhousing resembling a leaky rear seal or runny nose. The sending unit is right there above it as well. On the automatics the front seal is right there too. They are prone to leaking. Sniff test to make sure it's not tranny fluid. That said, if it's a drippy rear seal I would try using Quaker State All mileage 10w-40 convention oil, it has seal swell in it with a very high wear protection. Synthetics are great but will definitely find a leak if you have one, so I would avoid synthetics until you discover what's what. Good luck
Thanks for the input. I'll recheck all possible sources. I have procrastinated working on the problem for several years and have created other issues with sitting. First is to fix the brakes and then to the seal. I'm pretty sure it is the seal but will make sure. It appears to be coming though the slot on flywheel cover and started to spread under the car. Not sure how bad a rear seal would leak while driving and makes sense that a sending unit or valve cover gasket would come into play. Thanks again for things to check. I'll post what I find. I did a complete rebuilt on a 383HP when I was 18 so very familiar with the rope seals but all the posts with people having issues with the new seals brought me to the forum.
The rear main has always presented a challenge but in the last few years gasket and seal quality has suffered. I don’t know if is because of Chinese parts or what so it’s hard to recommend anything. Call 440source and ask them what they recommend. I will ask my engine building buddies what they recommend for the bbm, Joe buiilds plenty in a yeas time.
I’ve changed the rear seal on a 383 and a 440 while the engine was in the cars. I replaced with a rope seal using a “sneaky Pete seal tool”. It’s a tedious job. But can be done for sure.
One important key thing we overlooked.. On worn engines the crankshaft being as heavy as it is wears the lower main bearings down slightly causing a gap in the rear seal. You could check the main bottom caps for wear (thickness with micrometer) or eat your spinach and push straight up and down to check for play. Replacing the seal with a worn lower main bearing wouldn't help in that case. I recall a 400 engine with a severe rear main leak that had this very problem.
Last edited by Kuvasz101; Jun 16, 2023 at 05:14 AM.
Reason: Grammar
One important key thing we overlooked.. On worn engines the crankshaft being as heavy as it is wears the lower main bearings down slightly causing a gap in the rear seal. You could check the main bottom caps for wear (thickness with micrometer) or eat your spinach and push straight up and down to check for play. Replacing the seal with a worn lower main bearing wouldn't help in that case. I recall a 400 engine with a severe rear main leak that had this very problem.
I can agree with this, with all the work of installing the rear main seal new mains are a given. Just make sure of any oversize possibility installed and replace with the same…
