I have a vibration that I know is from one of two problems. One thing I found is the drive shaft is not inserted as far into the tranny as I would like. It can slide into the tranny 2", I know 3/4-1" is correct. I also can move the tranny tailshaft up and down. Not sure how much but is and 1/8" or more. So the questons are: Is the T400 rear bushing need replaced or does the driveshaft need to be longer? Or both, Thanks in advance

if you moving the output shaft up and down with out the driveshaft in there. the problem is bushing failures inside tranny. if driveshaft in and moving up and down you can try a tail bushing. also driveshaft needs to be a tad bit longer.

You should be able to move the output shaft some with the driveshaft out. This is normal even with all new bushings. The output shaft is kept centered by the yoke riding in the output bushing.
IF you have movement with the yoke in the trans, you have a worn (missing) output bushing and/or yoke.

I would say the tailshaft bushing needs replacement if you have over 1/8 inch of movement. The slip yoke is the deciding factor.

Measure the diameter of an unused portion of the slip yoke and measure the used portion, as seen by the scoring. I would think a diameter or 0.010 inch less than unused, you will need to replace the yoke.

To measure the depth of penetration of slip yoke into trans, marh the t/shaft housing on the outside the width of the bushing at the bushing location from within. Lower the car to the ground and measure from the yoke to seal. Pull out the slip yoke and measure the full length of yoke. Subtract the at rest dimension and subtract the bushing depth. The end of the slip yoke should be past the bushing. Ideally, the bushing should be in the middle of the slip yoke.

thanks for all the great info guys, I stuck a extra yoke I had in the tranny and you can move it up and down very little. I will measure the insert distance but I really think that is the problem. I guess it is not much work to change the rear bushing also.

People have a tendency to stick a driveshaft in without cleaning or deburring. They knock the driveshaft all around and then just stuff it in. It tears stuff up. I always polish mine and blow em out with solvent, wrap em in a big old rag while I get positioned.

Also they get full of crap inside the spline, and IMO that crap works out.

A tailhousing bushing isn't a big deal. Speedo cable worst part of it to me, hate to touch them if they work.:)

thanks for all the great info guys, I stuck a extra yoke I had in the tranny and you can move it up and down very little. I will measure the insert distance but I really think that is the problem. I guess it is not much work to change the rear bushing also.If the replacement yoke cured the problem, then its the yoke that's bad and not the bushing. However, not a bad idea to replace the bushing.

Remove the seal and pry out the old one, get behind it and make it smaller in diameter. Watch the seal bore, you don't want to add injury by scraping it, gouging it, bending it. A pvc pipe with cap makes a great bushing installer and an aid is to freeze it. Better to freeze with dry ice and then it will slide into place. Lube with oil. Install the seal.

Yes, a deeper depth does give more support and less wobble.