Drivetrain T5 leak - output shaft when on an incline

stangman16

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Nov 16, 2004
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I have a T5 in my '66 mustang which leaks through the output shaft when the car is on an incline. Had it towed, and it leaked loading and unloading while on an incline - practically poured out that rear seal. Rear seal was replaced some time ago and the appears to be no leak while the car is level and running..

I had bought this off someone who had supposedly rebuilt it and I ended up breaking a dog tooth and replaced it myself using a t5 rebuild book many years ago.. didnt notice any missing parts or have spare parts afterwards. All gears work fine now too.

Not sure if this is a WC or non-WC trans. Attached is a pic of the inside i had taken.

Is there something possibly missing inside the trans that I need to look at which should block fluid from draining out the output shaft while on an incline?
 

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Mustang5L5

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Was this T5 overfilled? The only thing that prevents the T5 from leaking out the rear is the tailhousing seal. There is a short and a long one, and it's possible that if the long one is used and the car is low, that the driveshaft does bump into it damaging it and causing a leak. Was the seal installed with some grease where the driveshaft rides against it?

The bushing inside will keep the output shaft from wobbling too much, but when the vehicle is static, the seal against the driveshaft yoke should still contain the fluid inside the trans.

When these transmissions are built and sold new, there is a plug that is installed on the mainshaft that fits into the bushing at the end. WHen the trans is installed at the factory, the driveshaft pushes this seal in. At this point it's no longer needed. When a virgin T5 is rebuilt, you'll usually find this black rubber seal on the mainshaft, but it does nothing to prevent leakage once a driveshaft is installed.
 

stangman16

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Nov 16, 2004
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San Antonio, TX
I filled the trans to where fluid starts to come out of the fill hole while the car is level.

I believe i have the short seal installed and I dont think I had used any grease where the driveshaft rides against it.

Are you thinking the seal got damaged?

On a side note, the driveshaft is the same one that went into my 4spd toploader, no changes were made to it or the yoke when I swapped to this T5.


Was this T5 overfilled? The only thing that prevents the T5 from leaking out the rear is the tailhousing seal. There is a short and a long one, and it's possible that if the long one is used and the car is low, that the driveshaft does bump into it damaging it and causing a leak. Was the seal installed with some grease where the driveshaft rides against it?

The bushing inside will keep the output shaft from wobbling too much, but when the vehicle is static, the seal against the driveshaft yoke should still contain the fluid inside the trans.

When these transmissions are built and sold new, there is a plug that is installed on the mainshaft that fits into the bushing at the end. WHen the trans is installed at the factory, the driveshaft pushes this seal in. At this point it's no longer needed. When a virgin T5 is rebuilt, you'll usually find this black rubber seal on the mainshaft, but it does nothing to prevent leakage once a driveshaft is installed.
 

Rdub6

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I have replaced the seal, havent touched the bushing. I suppose I could change that as well.
The bushing doesn’t keep the fluid in, but a worn out bushing will cause seals to fail pretty quickly.
 
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Mustang5L5

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If you grab the yoke of the trans, is there any up/down/side to side play?

If the bushing is failed, it will wobble and destroy the seal
 
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stangman16

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Nov 16, 2004
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If you grab the yoke of the trans, is there any up/down/side to side play?

If the bushing is failed, it will wobble and destroy the seal
Just got home and checked, it is the long seal, and the driveshaft seems to be slightly compressing it. I will change it for the shorter seal. When i touch the seal (the boot part) fluid leaks out. There is a slight wobble when i grab the yoke. Looks like you all figured out the problem. Thanks!

How do you get the bushing out?
 
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stangman16

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Nov 16, 2004
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Having a hard time finding the right tool and bushing installer. Found one that said for GM T5, would this work? Not sure of the differences in this area between Ford and GM. I know the shift area locations were different...
 

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Rdub6

So while I wait to figure out my rear end issues
Dec 29, 2017
2,660
1,967
133
Long Island, NY
Having a hard time finding the right tool and bushing installer. Found one that said for GM T5, would this work? Not sure of the differences in this area between Ford and GM. I know the shift area locations were different...
I’m not sure what stage of disassembly you’re in, if any, but I pulled the trans out. I removed the tail shaft and brought it to a shop to remove the old bushing and press the new one in. Cost me about $30 bucks!
 

manicmechanic007

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Make sure it is not the air pisser hole in the yoke that is leaking. I assume you've checked the basics like seal condition yoke diameter and bushing clearance and the garter spring is there. You will see pros like me put real thick grease on the splines. The ford stuff is teflon driveline grease XG-8A. You could try one of the splined rubber washers like Ford used on the AOD-E yokes in the late 80's. I have had to remove the yoke and braze up the pisser hole on the bitchy ones
 

stangman16

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Nov 16, 2004
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San Antonio, TX
Pulled the driveshaft and the yoke is trash. Fluid is leaking out the back of the yoke and it is worn with grooves on the surface. I will replace the yoke, u joints and bushing inside the tailshaft.

I notice I have about 3/4" from the yoke to rear housing - is this sufficient or will I need to have the driveshaft shortened?

Thanks again!