Trans Leak

01aford

01aford

Senior Member
I have a leak in my 40 transmission. It just started a few months ago and seems to be getting worse. Nothing huge a few drops every week when I pull it out (size of a quarter).
I'm sure it's coming from the front seal. I use straight 140 weight gear oil.

Any additives you guys know that will swell the seal and not damage my gears?
 
Its a lot of work but you might as well go ahead and replace it. It may still have the original leather seal and there probably isnt much left of it. While you have it out go ahead and replace the two small ones on the shifter shafts if its a side shift.
 
The main drive gear bearing baffle or oil slinger usually keeps the oil from going out the front. The later transmissions like the 49 to early 51 Mercury don't even use a seal there. I'd be more inclined to look for leaks from the back of the countershaft or even the front of the countershaft if it's getting loose in the housing. It's also not uncommon to get a crack there between the front countershaft bore and the main drive gear bearing bore. Engine rear main seal leak will also drool its fair share down to the bottom of the bell housing. You can tell that by the smell of the oil. That old 140 smells like crude.

Kerby
 
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