700R4 Tailshaft bushing and seal

[81Cheyenne]

Hi,
I'm having a chronic problem with my tailshaft bushing and seal backing out of the housing at highway speeds (70-75mph). This has been going on ever since I changed over to a 700R4 and a 12-bolt 3.73 posi rear end with heavy duty springs. I did have a 350T and a 10-bolt standard ratio with light duty springs.  I have already:
changed out the tailshaft housing, bushing and seal (twice)
changed over to a longer yoke (3/4" longer)
had new u joints installed and drive shaft balanced
I'm running out of ideas here. I've changed out about everything that I believe might be causing this. The only other thing that I can think of might be the drive shaft angle due to the truck sitting higher or possibly a bent output shaft. I haven't noticed a lot of vibration until the bushing and seal has already backed out.  Any ideas?

[Grim 82]

Is there a lot of slop between the output shaft and the splines in the driveshaft? It could be a bent output, or too much play in the splines. ?

[81Cheyenne]

There doesn't seem to be a lot of slop.  I've noticed that the output shaft does have some side play in it when the tail housing is off.  Is it supposed to have some slop?

[Irish_Alley]

how hard does the seal go in place?

[81Cheyenne]

The seal and bushing fit good.  I've raplaced both along with the tailshaft housing.

[81Cheyenne]

Still haven't found an answer....anybody?

[Grim 82]

Maybe there is too much play in the rear diff? Is the trans mount in good shape? I doubt it's your driveshaft angle, but it's entirely possible.

[HAULIN IT]

Does the yoke have a small hole in the center of it looking in near the U-joint? Some yokes have them & fluid drips out & appears to be the seal. Lorne

[VileZambonie]

Usually this means there is insufficient travel in the slip yoke and it pops the seal right out

[81Cheyenne]

After I changed out the rear end and springs is set up a lot higher in the back. If anything, the yoke wasn't quite long enough so I replaced it with a yoke that was 3/4" longer...still has plenty of travel and this one doesn't have a weep hole either....the bushing and seal actually rides out of the housing onto the yoke when it comes out.

[bake74]

  This is just a thought, you seemed to check all the major items over and over again.  Have you checked your new rear end where the seal sits to make sure it perfectly round and not bent a little, or if the surface inside is uneven or has a burr in it ?  In my line of work it often is the little things customers overlook and when I show up and it is a quick fix, they can't believe they overlooked it.  I always say check the simplest things first to save yourself some frustration.  Like I said just a thought.