21 Stud rear main leak??

70mach1

70mach1

Junior Member
I have a 21 stud flathead in my 35 Cabriolet and up to now the car has leaked only a very small amount of oil, a couple of drips in 2 months on my garage floor. I drove it some yesterday morning and about an hour after I returned home I noticed a big drop of oil every foot on my driveway. Peered under the car and in that hour I had a circle of oil about 10inches in diameter on the floor. It appears to be coming from the hole in the back of the pan under the flywheel (weep hole) which would indicate a probable rear main leak. With it becoming so bad so quick, does that mean the babbit let loose or cracked? Any other thoughts? I am new to flatheads, I am hoping there is an easy answer
 
I have a 21 stud also, 36, and have gotten some tutoring here during the assembly. It has a labrynth seal at the rear main in stock config, there isn't a rubber contact seal. Where I am going is with no rubber seal to leak, ever, if it has suddenly started to force oil through the labrynth, it may be due to pressure in the crankcase. Since it just started, perhaps the vent on top is clogged, easy to check as a start.

Assume oil qty is correct and you are not parked on a hill facing up?
 
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The oil level was down a little , didn't have any water or anything in the oil to raise the level suddenly. It is reading a half quart low on the dipstick, this is after the leak started, I haven't added any. I will check the crankcase vent filter. If you can think of any other reason why it would go from no leak to a rapid drip with no other changes let me know. Last time I drove it ( a week ago) no leak, yesterday leaking bad.
 
I also suspect elevated crankcase pressures. Check your breather cap and how it seats. Possible the ventilation is defeated by cap positioning?
 
was the eng overhauled with in the last few years? some of the gasket sets they sell today the rear seal is junk. they look like a piece of clothes line & fail in a short time. we get cars here at the shop all the time with that proulbem. we onley use n.o.s seals.
 
Peered under the car and in that hour I had a circle of oil about 10inches in diameter on the floor. It appears to be coming from the hole in the back of the pan under the flywheel (weep hole) which would indicate a probable rear main leak.
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That "hole" should have a big cotter pin in it. The pin just rattles around to keep the hole clean. There is a chance someone removed it thinking it doesn't belong there and the oil has been pooling behind some dirt that finally let go. Worth a look.
 
The 21 stud does not have a rear crank shaft seal, it has a slinger that slings the oil back into the pan, It could be the cork gasket that goes over the rear main cap to seal the oil pan. NOW. if the engine is all worn out and the mains have a lot of clearance they will leak. Ford didn't use a rear main seal until 46 on the 59AB engine. Walt
 
I had the exact same sequence of events with my '36, which has a babbitt-bearing 221 motor. What happened was the cork gasket between the 2 sections of the oil pan(the main section, and the flywheel "chamber" behind it) disintegrated. Went from the usual few drips to a gusher in one day. Dropped the pan and replaced the seal, all was well.

Adam
 
Adam/Mill Valley CA said:
I had the exact same sequence of events with my '36, which has a babbitt-bearing 221 motor. What happened was the cork gasket between the 2 sections of the oil pan(the main section, and the flywheel "chamber" behind it) disintegrated. Went from the usual few drips to a gusher in one day. Dropped the pan and replaced the seal, all was well.

Adam
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Adam, I had kinda come to that conclusion that the pan gasket may have failed. Thanks!!
 
I had the same issue, the first time the drain pipe was not on the rear main .The second time the cork outer seal had moved .With a 34 pan on a 36 block there may be a vent issue .Ted
 
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