Rear main seal
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Junior User
Joined: Aug 2003
Posts: 50
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From: New Jersey
Rear main seal
I have an 87 Bronco with a 351W and C6 tranny. I am pretty sure the rear main seal is gone, after driving it there is a puddle of oil underneath the rear of the motor and you can see where the oil is running down the front of the tranny plate. Just wondering if anyone has replaced one before and if rear main seals are a problem on these motors. It has 143,000 miles.
Elder User
Joined: Apr 2002
Posts: 813
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From: NJ
Rear main seal
actually what you describe sounds more like an oil pan gasket. usually when the rear main leaks the oil is on the inside of the bell housing, take off the inspection cover and see if it is wet inside. i would climb under there with a can of carb cleaner and some rags and clean it up really good and then make your decision. i thought i had a bad rear main and it was the oil pan gasket,this was no easy job either but i think it was esier then a rear main seal. just make sure exacly what is leaking because it stinks when you dont get it the first time.and remember it is always the simple things that trick us into thinking it is serious.
New User
Joined: Sep 2003
Posts: 4
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Rear main seal
I keep seeing people refer to the main seal or the oil pan... I had this problem. Turned out to be the valve covers. Check the bolts and/or replace the gaskets. They will leak down the back of the block and over the bell housing cover plate. I replaced my gaskets, properly torqued the bolts, no more leak.
Senior User
Joined: Mar 2001
Posts: 194
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From: Austin USA
Rear main seal
Just LAST WEEK I posted the exact same problem. Found out it was only the oil pan gasket (the rear seal to the oil pan gasket). That is why it is running down the tranny plate. See my post (heybrent) on the same topic for a ton of suggestions but DO THIS and you won't be disappointed. Unbolt the engine block (two bolts very easy) and jack it up 4-6 inches. Unbolt the muffler if it is in the way and take off the oil pan. I can almost BET it is the oil pan and the leak can be VERY decieving. The valve covers COULD be the problem as well but if you have EFI these aren't as easy to trouble shoot. You can almost BET it IS the oil pan gasket. I was losing 5 quarts every two days (that's how much the oil pan CAN leak). GOOD LUCK!
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Joined: Sep 2003
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Rear main seal
It could be any of the reasons stated in this thread. I, too, thought my Bronco's leak was the oil pan. So, like any half-a** shadetree, I jacked my engine up off it's mounts to change the oil pan gasket. That came to a stop when the upper intake manifold hit the firewall. Ended up having to pay someone to finish the job. Didn't stop the leak. Not long after, I changed the transmission fluid which started the tranny slipping. Ended up having the tranny rebuilt. Asked the mech "since you have the tranny out, throw in a new rear seal". He said I didn't need one, no leak there. Lastly, I replaced my valve cover gaskets and properly torqued them. Leak gone.
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Junior User
Joined: Aug 2003
Posts: 50
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From: New Jersey
Rear main seal
Thanks for all the replies. It is not the valve cover gaskets, there is no oil running down the heads. I am pretty sure it is a combo of the oil pan gasket and the rear main. The left side(drivers side) of the oil pan is covered with oil from about the middle to the back. And there is also oil dripping from the back side of the tranny cover, not the front. I actually just bought the truck a month ago, and it is not my daily driver, just something to have fun with on the side, and fix up (although it is in excellent condition already) and modify even more. I have been driving it lately and it only leaks when the motor is hot, once it cools off, the leak is gone 100%. I am gonna just leave it until next spring. I have an engine lift and a tranny jack and I have pulled and installed motors and trannys a couple times so this is a job I can handle. I have put about 200 miles on it sine the last oil change and have not needed to add any oil yet. btw, it is not the EFI, it is a 4bbl
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Senior User
Joined: Mar 2001
Posts: 194
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From: Austin USA
Rear main seal
I am telling you...it is a 5 hour job with minimal stress to replace the oil pan gasket and whala no more oil leak 
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Senior User
Joined: Mar 2001
Posts: 167
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From: Corona, CA
Rear main seal
Also check your PVC, mine had become disconnected and was leaking oil all over the place when I did the Injectors last week I discovered the reason why, some nimrod had ziptied it to a wiring harness so when I popped my engine mount last winter it pulled out the hose.
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