Blowing through U Joints

[mtully79]

I took my 72 down to 6 inches from 8, and now I'm burning through U joints every few hundred miles or so. What setup has anyone seen that works well for these trucks?

It's not a mudder, and will only see roads and dunes occasionally.

[jaros44sr]

Originally Posted by mtully79

I took my 72 down to 6 inches from 8, and now I'm burning through U joints every few hundred miles or so. What setup has anyone seen that works well for these trucks?

It's not a mudder, and will only see roads and dunes occasionally.

Is there enough room on your slip joint, which u-joints are breaking

[cleszkie]

Since you say you had an 8 inch lift, I am going to assume that you have a CV joint at the transfer case end of your rear driveshaft, and that you had the rear pinion pointing straight at the CV joint when the 8 inch lift was in. Did you adjust the pinion angle on the axle by either rotating the perches or adding shims? If not, you probably have a misaligned driveshaft, and your pinion is probably pointing up too much. This would lead to shortened u-joint life at the pinion.

[hemi43]

Something mechanical is wrong !! Having the pinion angle off would not cause the u-joints to fail in such a short time. I agree with Jaros that maybe you're bottoming out your slip yoke. Poor installation of the cups, or a damaged yoke could also lead to premature failure. If you installed these yourself, did you make sure there was no binding after the c-clips were installed?

[mtully79]

Originally Posted by jaros44sr

Is there enough room on your slip joint, which u-joints are breaking

The u joint at the top of the rear drive shaft is having the issue. It was lowered by a shop here in Va Beach using BDS suspension kit. I don't know for certain what the angles were prior to lowering it. Stock drive shaft and yoke, never been altered by me since I've owned it.

[mtully79]

I installed replacement U joints myself hemi43, and no binding after install. And no CV joints on the vehicle, was wondering if that was my fix.

I appreciate the feedback gentlemen!

[GMC-YA68]

You can run a factory rear driveshaft with a 8" lift?

[tjsblazer]

I doubt that is a factory shaft. When I bought my Blazer it had a 4" lift and the factory shaft splines were stretched out as far as I would be comfortable with.

[hemi43]

Hopefully we find out what's wrong. I know too little, or to much angle (within reason) will damage a U-joint, but it takes a long time, sometimes thousands of miles. This is why I suspect some sort of mechanical interference if it's happening within a few hundred miles. I once had a car that ate U-joints, and it ended up being a yoke that had an oval cup bore. I'm still betting on a binding slip yoke. Like Jeff and others have said, more than likely the shaft was longer than stock to accommodate the 8" lift, and now it's too long with a 6" lift and bottoming out when the suspension is under compression.

[GMC-YA68]

Are you feeling like you are having any axle wrap while under acceleration?

[mtully79]

I never really 'get on it' and have never felt any axle wrap. I'll hear a ping when I shift from Park to either reverse or drive which alerts me to the issue happening again. Truck was purchased at 8" lift, and I've never measured the drive shaft...I'll do that tonight and compare to stock length. Yolk is the next thing I'll take out and have a friend who is more mechanically inclined take a look at and see if there is any obvious signs of defect.

[jaros44sr]

Originally Posted by mtully79

I never really 'get on it' and have never felt any axle wrap. I'll hear a ping when I shift from Park to either reverse or drive which alerts me to the issue happening again. Truck was purchased at 8" lift, and I've never measured the drive shaft...I'll do that tonight and compare to stock length. Yolk is the next thing I'll take out and have a friend who is more mechanically inclined take a look at and see if there is any obvious signs of defect.

When you get a chance, measure your driveshaft, and I'll measure mine, since I've a 4" lift, see if the answer lies there
Whenever I have a problem, I return to the last thing I did, and undo it

[jaros44sr]

Any new updates?....

[mtully79]

Been busy with work and "honey do" projects at home...the joys of marriage.

Plan is to measure the drive shaft tonight with a couple pics for reference. Weather is improving so I'll see if the shop can have a look at it when I have a couple days of sunny weather.

[cleszkie]

Definitely measure how much travel you have left in the slip yoke before it bottoms out. As mentioned above, if you don't have enough travel left to counteract the shortening of the driveshaft upon compression of the rear suspension, the driveshaft will want to force its way into your transfer case straight through the u-joint.

[hemi43]

Originally Posted by mtully79

Been busy with work and "honey do" projects at home...the joys of marriage.

Plan is to measure the drive shaft tonight with a couple pics for reference. Weather is improving so I'll see if the shop can have a look at it when I have a couple days of sunny weather.

Measuring isn't really going to tell you anything. You need to unbolt the rear U-joint from the differential yoke, and collapse the slip yoke to see how far it will go before it bottoms out. If you only have 1/2 inch of travel, that would explain why you're chewing up u-joints. My 2 cents.

[mtully79]

Originally Posted by hemi43

Measuring isn't really going to tell you anything. You need to unbolt the rear U-joint from the differential yoke, and collapse the slip yoke to see how far it will go before it bottoms out. If you only have 1/2 inch of travel, that would explain why you're chewing up u-joints. My 2 cents.

Roger that, I'll pull and measure this weekend. Thanks for the tip.

[jaros44sr]

Originally Posted by hemi43

Measuring isn't really going to tell you anything. You need to unbolt the rear U-joint from the differential yoke, and collapse the slip yoke to see how far it will go before it bottoms out. If you only have 1/2 inch of travel, that would explain why you're chewing up u-joints. My 2 cents.

I was just thinking, if our driveshaft are the same length, then it wasn't lengthened for the lift. If it was measured yoke to yoke, I wouldn't have to drop my driveshaft...

Am I wrong in my thinking?

[hemi43]

Originally Posted by jaros44sr

I was just thinking, if our driveshaft are the same length, then it wasn't lengthened for the lift. If it was measured yoke to yoke, I wouldn't have to drop my driveshaft...

Am I wrong in my thinking?

Sorry Jaros, I'm not quite sure I understand your question.
I would still drop the shaft and check to make sure there's enough travel in the slip yoke. Another problem could be a corroded slip yoke. If it's seized up, it will cause problems. Disconnecting the shaft (which takes 5 minutes) will answer many questions.

[mtully79]

It's been a minute since I was on here, between a move and a new baby(can there be an old baby?) I was MIA. Installed a new shaft with more travel and that solved the issue.