Ok here's the problem about 2 years ago I put a posi and a set of frpp 4:10 gears installed since then i have had a virbation and because of it I have had to replace the rear bearing and race 5 times 3 trans tail shafts. 2 diffrent shops have done the work the last time I had it done was 700 miles ago to evacuate for katrina by the time I got 3/4 of the way back the bearing was screaming at me. The vibration starts at 78 mph and just get worse the faster I go. I have had the drive shaft balanced & the vibration is still there. I have asked both shops if it could be in the gears and they said the gears and setup look fine.Any idea HELP!!!!!

This is what the bearing race look like after 700 miles:
<img src="http://fordtruckworld.tenmagazines.com/gallery/WhiteWizard/609298.jpg"><br>

 

Is your truck lifted or lowered?

Have you checked the angles of the driveline at the tranny and rear end? Are they equal?

The picture gives me the impression that the pinion preload was to great. Was the 'crush sleeve' replaced each time the bearing was replaced?

Did you 'skimp' on the bearing? Easy now, just asking, I am not trying to imply anything. But I have had Autozone bearing fail rather quickly. I have had the best luck with Timken bearings. Have you examined the other bearings in the rear end? I am wondering if you may have a wheel bearing out and shavings/pieces from them are contributing to the bearing carnage.

I would also like to suggest that you spend some EXTRA time cleaning the differential housing. Make double sure that everyting is clean before reassembly.

Lastly, use a good quality oil/grease. I like the AMSOIL 85-140, but that is me.

Good luck.

 

I agree with the above, I'm thinking you've got a pinion bearing preload problem. Pull the entire housing down and throughly clean it, I'm talking go through a bunch of brake clean or solvents or whatever you have, get it as clean as possible. Also, inspect the tailshaft bushing at the transmission, to make sure the front slip yoke isn't flopping around or loose or anything.

 

1:Ok the truck is lowered 2 /4 and the local ford deal did a drive line check and said the angles where fine. did'nt get to see this done tho.
2:the the crush sleve and pinion nut where replaced ea. time
3: last time the rearend was down I replaced all the bearings clutch packs with ford parts and motorcraft gear oil and I watched him install all the new parts when it was last done.
This time I am going to do the job my self and spend the extra time cleaning the housing and parts. and all ready bought plenty of brake cleaner that was my thinking the was dirt or trash in the housing some where. but the vibration is there from the start after ea. bearing reinstall.Could it be pinion bearing shaft warped or out of round?

And Thanks for the Help!!!!!!!!!!!!

 

Was the Driveshaft Length changed when the vehicle was altered (lowered)? Was the pinion angle changed, by rewelding the spring mounting brackets or using wedges at the spring mounting points on the axle mounting brackets to accomodate the change in pinion angle?

 

6 degree shims where installed and no the drive shaft is still factory length.
its a belltech 2/4 lowering kit . The thicker part of the wedge is facing to the front of the truck.

Thanks for the reply's

 

Too much preload. The bearing cup has spalled due to overloading.