Question: tranny tail shaft seal

[SRReality]

The tail shaft seal in my Muncie 4-speed is leaking. Can I replace that with the tranny still in the car? It appears to me that if I drop the drive shaft, remove the cross member and support the tranny, I can get to it under the car. Am I kidding myself?

 

[Tom Bryant]

No need to pull the tranny for that. It should be easy once the drive shaft is out of the way.

Tom

 

[Hib Halverson]

As Tom Bryant says, you can replace the extension housing seal without removing the gear box, but....

In many cases of older transmissions, a leaking output shaft seal is a symptom of a failed extension housing bushing. Replace the seal. If the new one leaks or starts to leak soon after installation, you proably have a worn extension housing bushing and the ouput shaft is moving off center enough that it the seal cannot conform to the moving seal surface.

In fact, if the extension housing bushing has failed, you probably need to overhaul the gearbox.

 

[SRReality]

As Tom Bryant says, you can replace the extension housing seal without removing the gear box, but....

In many cases of older transmissions, a leaking output shaft seal is a symptom of a failed extension housing bushing. Replace the seal. If the new one leaks or starts to leak soon after installation, you proably have a worn extension housing bushing and the ouput shaft is moving off center enough that it the seal cannot conform to the moving seal surface.

In fact, if the extension housing bushing has failed, you probably need to overhaul the gearbox.

The gearbox is in good shape. Could it have anything to do with this being an M21 Muncie from a '64 Corvette, installed in a '62? Is the output shaft different size between those years? My theory has been that I don't drive it very much and the seal has dried out. I had planned to replace the bushing and the seal anyway, but wondering why it has happened if "drying out" isn't the real cause.

 

[Hib Halverson]

Support the car on stands. Get underneath, get a good grip on the ouput yoke or the driveshaft and push up and down real hard. There should be little or no movement. If there's a lot of movement, the extension housing bushing might be shot, the yoke might be bad or the output shaft is worn. If you have any of those problems, other parts of the gearbox may need attention.

If there is no movement, just replace the seal and chalk it up to age.

If there is a lot of movment, you can replace the seal but don't be surprised if the leak returns.

 

[SRReality]

Support the car on stands. Get underneath, get a good grip on the ouput yoke or the driveshaft and push up and down real hard. There should be little or no movement. If there's a lot of movement, the extension housing bushing might be shot, the yoke might be bad or the output shaft is worn. If you have any of those problems, other parts of the gearbox may need attention.

If there is no movement, just replace the seal and chalk it up to age.

If there is a lot of movment, you can replace the seal but don't be surprised if the leak returns.

That's what I'll do! Thanks for the help!

 

[maxphunn]

Something else to consider...

The gearbox is in good shape. Could it have anything to do with this being an M21 Muncie from a '64 Corvette, installed in a '62? Is the output shaft different size between those years? My theory has been that I don't drive it very much and the seal has dried out. I had planned to replace the bushing and the seal anyway, but wondering why it has happened if "drying out" isn't the real cause.

I could be all wrong on this, my memory is fading...

When you put a Muncie into a C1, aren't you supposed to change the angle of the driveline with shims or spacers at the tranny mount?
I think a different driveshaft yoke (shorter?) is recommended as well.

 

[SRReality]

Yet another thing to ask!

I could be all wrong on this, my memory is fading...

When you put a Muncie into a C1, aren't you supposed to change the angle of the driveline with shims or spacers at the tranny mount?
I think a different driveshaft yoke (shorter?) is recommended as well.

That I don't know. I bought the car built the way it is. It appears to have spacers on the tranny mount (several extra washers), but I don't know about the shorter yoke. Where would I find out for sure? And if I need a shorter yoke, where to do I get one?

 

[maxphunn]

That I don't know. I bought the car built the way it is. It appears to have spacers on the tranny mount (several extra washers), but I don't know about the shorter yoke. Where would I find out for sure? And if I need a shorter yoke, where to do I get one?

I think I got mine from Paragon Reproductions.

I'm not saying that the yoke caused your problem, just that you may want to check to see if the Muncie conversion was done right while you are working in that area.

 

[SRReality]

Just enough mechanical ability to be dangerous

I think I got mine from Paragon Reproductions.

I'm not saying that the yoke caused your problem, just that you may want to check to see if the Muncie conversion was done right while you are working in that area.

I hear you about the yoke, but I don't know what to look for to see it was "done right"........other than all the other work was well done, very tidy, there are no shimmys, vibrations, clanks or whines. I pushed and pulled on the front end of the drive shaft......didn't feel any play, so to my limited knowledge, it appears fine......except the seal leaks! So, I'll "borrow a lift" and see what I can fix! But, first, Jim Beam and I are going to sit on the back porch and ponder it awhile.

 

[JohnZ]

The '64 Muncie in a '62 is a simple swap - all it needs is the adapter plate for the trans mount (that was used on ALL '62 4-speeds) that moves the two vertical trans mount bolts forward a couple of inches from the '56-'61 location, and about 1/4" of spacers between the trans mount crossmember and the frame to move the trans down a bit for correct driveline angle. It still uses the original "long" (4-1/2"-long tubular section - photo below) front yoke; ALL C1's, regardless of transmission, use the "long" yoke, which was ONLY used on Corvettes, to compensate for the amount of fore-aft movement of the front yoke that results from the extreme driveline angle as the rear axle moves up and down. Passenger cars used the "standard" (3" tubular section) yoke.

 

[SRReality]

The '64 Muncie in a '62 is a simple swap - all it needs is the adapter plate for the trans mount (that was used on ALL '62 4-speeds) that moves the two vertical trans mount bolts forward a couple of inches from the '56-'61 location, and about 1/4" of spacers between the trans mount crossmember and the frame to move the trans down a bit for correct driveline angle. It still uses the original "long" (4-1/2"-long tubular section - photo below) front yoke; ALL C1's, regardless of transmission, use the "long" yoke, which was ONLY used on Corvettes, to compensate for the amount of fore-aft movement of the front yoke that results from the extreme driveline angle as the rear axle moves up and down. Passenger cars used the "standard" (3" tubular section) yoke.


View attachment 4383

Thanks, John! When I have the seal/bushing changed, we'll use this info to make sure the spacers are in there correctly. That could be the reason the seal/bushing has failed.

 

[SRReality]

Just to close this one out...........the yoke, the drive-line angle, etc. all were "OK" - - - tailshaft seal itself was actually "OK", but the bushing inside was not. Had that replaced and a new seal. So far, looks like that did it.

 

[Tom Bryant]

That's good news. Sometimes the simplest things make the biggest difference.