There are many possibilities but I would look carefully at the driveshaft - u-joints and balance.  You may have had a balance weight extract itself.  In some cases what you can "feel" in a u-joint by moving it by hand is not what it does under load.  I have a co-worker that lost a u-joint at greater than highway speeds and the carnage included breaking the tailhousing off the transmission and ripping the front out of the bellhousing - so this is not something I would wait and see on.  Replace them both and have it balanced.  If its cured you are in good shape if not, you have eliminated one possiblility.

Also, since you ran with no slide in the tranny yoke, you may have trashed the input shaft to main shaft bearing in the tranny which could do the same things you are seeing.

Adam's a buddy of mine so I can report that the driveshaft has been replaced with a new correct length unit (presumably properly balanced), u-joints are new, slip yoke is new, clutch is new with new pilot bushing and the tailshaft bushing has been replaced as he noted. Here's a pic he sent of the new output shaft seal that came apart within a couple days of being replaced. Might be a little hard to see but the seal flange and some of the seal separated and are riding at the front of the yoke.



I think DC may be on the right track (unfortunately) and the tranny might need some internal attention, makes sense that a drive shaft with no freeplay would hammer pretty hard on the tranny bearings. The guy working on the car said that both the pilot bushing and the tailshaft bushing were out of round and a couple of the bellhousing bolts (I think the bottom two tranny to bellhousing) were stripped out.

Another thought, with bad motor mounts and the two lower bolts not really holding the tranny to the bellhousing tightly seems like you'd have kind a pivotpoint at the top two tranny bolts constantly messing with tranny to crankshaft centerline relationship which could partly explain some of the damage seen so far. Just thinking out loud here, don't really have a lot of experience with this kind of problem.

Last edited by McStang (4/05/2013 12:12 PM)

Thanks for the ideas guys. My mechanic is stopping by my place tomorrow to put a new seal on. I'd like to remove the transmission extension and check for free play.

I'll also check the motor mounts, fan and harmonic balancer. Not sure about the tranny mount.

The drive shaft, U Joints and slip yoke are all new as of last week.

I'll keep you guys posted.

Thanks

Adam

The guy working on the car said that both the pilot bushing and the tailshaft bushing were out of round and a couple of the bellhousing bolts (I think the bottom two tranny to bellhousing) were stripped out.

, with bad motor mounts and the two lower bolts not really holding the tranny to the bellhousing tightly seems like you'd have kind a pivotpoint at the top two tranny bolts constantly messing with tranny to crankshaft centerline relationship

 That alone would be enough to "tear up" a tranny,in my book.
Bet that's causing the problem!!
6sally6

Not 100% sure yet but I'm thinking its the transmission. If I do end up replacing the T-10 I'm interested in putting in a T-5.  What should I look out for when sourcing a replacement and what sort of modifications if any would be needed for the swap?

With all of the posts I've received and doing some other research I feel like the drive shaft being too long caused a chain reaction. Since the drive shaft was pushing into the tail of the transmission it wore out the bushing and has proceeded to beat the hell out of the gearbox.  Also, since the drive shaft was pushing into the transmission extension it caused the bottom two bolts on the bell housing to strip out. Seams to make sense.

McStang and I have been wrapping about it for a minute and I think its time for a replacement.

Let me know what you guys recommend for a replacement.

Any recommendations on t-5 models, bell housings and first gear ratios for a 289 with 3.25 rear? A reasonable first and second gear are needed. Reality of living in the hills of San Francisco. Also my 289 seems to have a mild cam but not putting out more the 300 hp. Thinking about putting hi-po exhaust manifolds for my dual exhaust setup and cable clutch while I'm at it. 

Along with your driveshaft and u-joints that can change under load versus coast, up-hill, etc., it also sounds like it could be a shift in driveline angle.  I can't see how that would happen suddenly unless you dropped a shim or broke a perch/mount on the rear.  Can you measure your driveline angle and pinion angle to make sure you are about 3 degrees on the engine/transmission and perhaps 2 degrees up on the pinion?  If the pinion is rotating up excessively it could cause the vibration you describe if it does it under load and not while coasting.  I love to spend other people's money but I would change the u-joints just to make sure you are not fighting a problem that you can't feel when twisting them by hand.

So I had some help and pulled the transmission out over the weekend.  My new slip yoke is showing extensive wear for being less than two weeks old. Also the output shaft isn't balanced.  Its easy to see the output shaft is bent if you manual spin the input shaft.

Looks like I found the cause of the vibration.  Long driveshaft really did a number on the old bird. All that banging against the extension ruined a perfectly good T-10.  Luckily the rest of the tranny seems to be in really good shape. 

I'm on the hunt for another T-10 output shaft and slip yoke.  Let me know if you guys know of any sources for the output shaft.  Yoke seems to be readily available.

Thanks

the1stman wrote:

.....My new slip yoke is showing extensive wear for being less than two weeks old. Also the output shaft isn't balanced.  Its easy to see the output shaft is bent if you manual spin the input shaft.

Had this happen with my T5 in less than a month of driving as well. Had an extra 3/4" taken out of the Aerostar aluminum driveshaft and rebalanced at the company's cost that did it the first time.