904 tailshaft mystery leak.

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JoePole1

JoePole1

A dude in a B body
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So I have this annoying trans leak at the back of my 904 and it's got me scratching my head.
Thinking that it was the rear seal or possibly the bushing, I replaced both a couple of years ago. The tailshaft is completely dry and so is the yoke but you can see the spray pattern above the u-joint. The leak is not heavy (occasional drips) but it gets flung around. It's been going on a few years. Most times I take a ride I wipe it down afterwards.
The picture is from my car that has been sitting for over 2 months. I had wiped everything down prior to that. It almost looks like it's coming from u-joint. Definitely trans fluid.
Got any ideas?

IMG_20210319_160554_hdr.jpg
 
Any chance that it's leaking through the yoke? If the outside of the straight part of the yoke is dry, I couldn't see where else it may be coming from?
 
Yeah, I was taking a shot in the dark. I think the slip part is welded to the u-joint part so I though there might be an issue there:(
 
That Front Yoke could be welded on there and leaking through pin holes in the welding.

Swap on a different front Yoke and see if it quits leaking. Or clean and seal the outside center of the slip tube at the yoke slip tube area with RTV gasket maker.

There probably is a centering point there too for turning on a lathe that may have been drilled too deep causing the leak.

Have to clean up that area on the yoke and have a look. Can even test the splined slip tube area with some air pressure and see if it leaks out by the u-joint.

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Kind of looking like one piece yoke here but could be a pin hole of some sort in the casting.

20210320_064201.jpg


Take some brake parts cleaner on a wrag right behind the rubber tail shaft boot and get that part of the shaft dry. Let sit for a while and see if it gets wet on the shaft again.

Capillary action can pull the fluid from that seal area too.
 
Can try ^^^ squeezing that tail shaft dust boot and see if any fluid comes out from there,

There is supposed to be a weep hole in the bottom of that dust boot to let oil out if it gets past the rear tail shaft seal.

Someone could have installed it with the weep hole up, creating a collection point for trans fluid.
 
Looking at it again, where the spray pattern up in the tunnel is, I would say it is the tail seal that is leaking even though new 2 years ago.

That slip tube on the Yokes can have rust pits in them from over time. They can have a groove cut in them too where the seal runs, both causing slow leaks.

Sometimes you just have to put on a new yoke/slip tube to get a new sealing surface for the tail seal. New seal too at the same time.
 
^^^ That's the sucker that comes to mind, the one with that drilled hole, good job finding a pic slickchick .
 
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George is correct, have seen this before. Oil is migrating down the splines and exiting the back plug in the yoke. Since there is no oil pressure there, you can repair by cleaning the area and apply silicone around the edge of the plug.
 
Murray said:
George is correct, have seen this before. Oil is migrating down the splines and exiting the back plug in the yoke. Since there is no oil pressure there, you can repair by cleaning the area and apply silicone around the edge of the plug.
Click to expand...

Seems to me I heard a few years back, someone coated the spline grooves in the slip yoke with grease to create a dam to help keep the trans fluid from getting to that yoke plug. ^^^^^

That plug area sounds about right as far as the leak.
 
I may be wrong but I believe the yoke is one casting ( maybe a forging).

Then it is machined.

I believe the center of the yoke has a form of freeze plug in it.

Maybe that's where the leak is comming from?
 
Thanks guys. The boot is bone dry so looking like the yoke center may be the culprit. Sounds logical. I'll pull the prop shaft and check the "plug".
 
Just a follow-up on this thread. I finally pulled the prop shaft, cleaned the inside and outside of the yoke with CRC spray cleaner and sealed the plug on both sides as recommended by you guys. Reinstalled and let it dry. Took the car out for the first ride of the year today. No Leaks!!!! Thanks to all for your help.
 
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