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Got it installed, oil leaked right out through the bottom center hole under the door cover. My old trap door did not have this hole. The hole is threaded. If I stick a q-tip thru it, I can see it inside the transmission.
What is this hole for, and what would it be called? Couldn't find anything about it. What to do about it?
If it is simply a plug, anyone know what size? Maybe I can get it done at an Ace Hardware.
Probably a threaded hole for exhaust mounting bracket. Get the correct size screw/bolt, put some good thread sealer on it and plug it up.
From the website:
Features:
This is a cost-effective way to replace your worn or cracked trap door with an OE spec unit.
This Chrome Plated Trap Door features an ear with a threaded hole for an exhaust hanger mount.
Made from Cast Aluminum specifically for Harley 5-Speed Transmissions
It's making more sense now. I saw the part about the exhaust hanger, but was thinking they meant the two other hangers. So thanks for pointing that out.
I think the hole is 3/8-24. If I could find a big hex head set screw locally, I'd seal it up with that rather than hunt for and wait for OEM.
Then we are not talking the same language because the hole is much larger than 1/8". But maybe I am understanding something wrong, I don't know much about NPT.. I can say with confidence at this point the hole is larger than the 5/16" door mounting holes.
A 1/8 NPT plug is bigger than 1/8 inch. Don't try to indiscriminately screw fasteners into the threaded hole until you verify the thread pitch. Like others here have told you, it's a drain plug for use in Softail applications. Take your time and think things through when working on your motorcycle. Getting in a hurry will only cost you money replacing things you mess up.
That hole is for a drain plug, used on EVO Softails.
Part number 739A.
Yes, it is a 1/8" pipe plug, and yes, it is way bigger than 1/8".
Plumbers must use special rulers
Since your transmission has a drain plug on the bottom, you don`t need a drain plug in the trapdoor, you just need to fill that opening.
Go to a hardware store and get a 1/8 pipe plug (Allen wrench type), wrap some Teflon tape around it and snug (snug, not tight) it into the case, and forget about it.
Don`t use the 739A part, it has a magnet on it, so you would need to remove it periodically to clean it off, no need for that magnet because your bottom drain plug has one, and the less you mess with a tapered pipe plug, the better.
Last edited by Dan89FLSTC; Apr 21, 2025 at 10:24 AM.
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Trap Dorr replacement extra hole
