Hi guys
Got a good one for you.
My truck has always eaten through rear ujoints about every couple years.
Few weeks ago I replaced the rear and the new one failed in two days.
Replaced it with a Moog heavy duty and it failed in two days.
Replaced it with another Moog heavy duty and it failed in two days.
Got another Moog heavy duty and replaced it on my bench taking painstaking time to lube and make sure all is well.
Failed in two days. So that's four joints.
Obviously I took every precaution installing. All is perfect and in place.
My truck doesn't stutter letting the clutch out.
I have traction bars so no crazy movement. I broke them with and without the traction bars in place.
Ideas?

 

How hard are you torquing down the u-bolts at the back? Too tight, and you'll crush the bearing caps, which can lead to premature failure. I think the spec is like 15 ft-lb.

 

Don't scratch too much, it causes baldness..

Is the drive shaft balanced?

What shape is the transmission mount in?

Is there any extra play in the pinion?

 

Well I am putting more than 15 lbs on them but never had a problem before.

To late

Recently had the drive shaft rebuilt at a real good drive shaft shop.
Tranny mount is old but in good shape.
Pinion only seems to have gear lash play but I have not looked for wobble.
The fact that it's always the diff side is troubling though.
May be a combo of both of your thoughts.

 

Recently had driveshaft work done ... I might look there for any potential causes too.

 

Pinion angle correct?

 

Well, now we're really getting into it.
The short answer is, no.
I've been working my way back to the rear end from the front.
So when you do that and all your improvements start to have an impact on your un improved places this stuff happens.
However, going through u joints every 18 months to two years I figured was my penalty for letting that slide.
This is another story though. All the sudden breaking them after two days is a bit different.
So no, my angle is not optimized, but I'm getting to it.
I just have a 3 inch lift so shouldn't be to big a deal there but you are correct to ask especially when you throw in a 500 ft/lb engine into the equation.

 

Very strange..sounds like ya got the bases covered with the above responses, i.e. pinion angle.


But ask Cammer what is going on.. he'll sniff out the problem.

 

Funny you say that. I'll be under the truck and all of the sudden I'll get a ball tossed at me with him standing there with this sh_t eating grin on his face.
"C'mon throw the ball. Screw that truck"
Makes me smile.

 

maybe a dumb question but are the U joints in phase?

 

Yes sir and not a dumb question.

 

I recently did joints on my '78 F250 (PM for the originals!). First set I got were "premium" NAPA. Distance from end to end on the cross was too large and they wanted to bind. I tried "premium" AZ joints and fit was good. No binding and no problems. Ouch for NAPA!

Possible something like that is going on?

Another possible problem is pinching the driveshaft ends. I had that on my front axle shafts. It took a lot of press force to get the 35+ YO originals out and it pinched the ends in a little. I had to set up the press to expand them a bit afterwards to prevent binding with new joints.

A digital caliper was my "helper" on the above situations to figure out what was going on. Old joint vs new and joint vs driveshaft dimensions.

 

Entirely possible.
Though they fit well to the eye.
I may have time tomorrow to diagnose some more.
I'm going to go to the driveline shop and get a different (brand) set of joints and new hardware.
I'm willing to believe I'm over tightening but I've been doing this my whole life and this is the first time I have had a problem.
I'll break out the caliper and give it a good going over.

 

I would expect over-tightening to take longer than a couple days to show problems ... but it was something to check. The alignment/tolerance suggestions are probably closer to the mark.

 

I agree.
It's shattering the bearings in short order.