Driveline vibration

[blue bronc]

Here is the deal.
I had my transmission rebuilt in 12/08. Have not had any trouble with it.
About three weeks ago I was on my way to the auto store and started have this loud nock under the bronco in the transmission area. It was obvious that something was very wrong. Luckily I was only a couple of miles away form my transmission guy so I limped it to his shop and left it for him to check out. He called me right away and said that the rear drive shaft was shot and had a lot of play in it and that is what was rotating and hitting the floor. So I took the shaft to a recommended shop and they rebuilt the entire thing. All new u joints CV kit. I installed the shaft and went on my way. I have noticed in the last two weeks that there is a nock that can be heard from the inside of the cab. Not a bad nock but it can be heard. It will nock when under load or between 1500 and 1700 rpms.
Yesterday I took it to the transmission guy and we checked it out and ruled out the transmission.
The nock has to be the drive shaft.

My question is if I take the shaft out and have the shop check it out and it is balanced and good. What am I left with option wise?
Can you install the shaft incorrectly?
I know that you cannot tighten the ubolts too tight I made sure not to torque them down.


For background: 77 bronco with 5.5 lift and 33/12.50 stock 302 with auto C4 and Dana 20 I understand that the drive line angle might be a little steep but I did not have this problem with the last shaft. Till it went out.

Any ideas would help.
Thanks Mark

 

[Traveler]

Your next step is to pull the shaft and check it again. A lot of things can happen. Sometimes grease does not reach all 4 caps when greased. They could have put it together incorrectly. Who knows.
They should at least check it for free though.

Beyond that, there could be a problem with the tranny or rear end that the tranny guy can't find yet. He did the easy thing and said, not my problem, instead of finding it for you.

 

[Viperwolf1]

Check the rear output on the tcase. It shouldn't have any slop in it. You shouldn't be able to move the yoke up and down or sideways. Same thing is true of the rear axle pinion.

 

[peteacher]

Also check the cross member bolts to make sure they are tight, as well as the bushings/ bolts in the transfer case mount. I found that my body mounts were so bad that the rear drive shaft yoke would contact the floor under load. New body bushings problem solved.

 

[SHX669]

Another thing i've found is that with a suspension lift of 3 1/2 " or more the driveline angle is too steep . Add a 6 degree axle shim . It greatly increases the longevity of the u -joints and smooths out the vibrations . My son was going through a u -joint a week -- on the hiway ; untill we added the shims.
SHX
Oh ; all drivelines aren't the same . Some have different "CV yoke " sizes and different "tube" lengths

 

[blue bronc]

OK i dont have much hair to begin with and this is causing it to fall out faster.
I took the shaft to the shop that built it and they did a recheck.
It balances and all the parts check out.
In responce to the replies.
I checked there is no slop in the drive line
I already have the 6 degree shims and all the bushings on the body and the
t case are good.
Is it possible that in the couple of miles that i drove it to the shop to have it checked when the shaft originally went bad that i bent the shaft in the tcase and that is what is making the rotating sound?
It only makes the sound under load. it does not have to be heavy load just some amount of load till the shaft is going so fast you cant make out the sound.