U-joint problem

After 35K miles, I've had 2 rear u-joints fail. It's a t-bucket -sbc, 4-speed. ford 8" rear. Engine & trans. is 2* down, pinion is 2* up, driveshaft is at 0*. Normal suspension travel is about 2" up/down. Driveshaft is 13" long. Frt. u-joint is still the one I started with. They are the "good" napa greaseable joints. Anyone have any idea why I'm experiencing what I consider to be "early" failure of the rear joint?

Thanks , dave

 

Does the rearend wrap any under power?

 

I wouldn't think so , it's a pretty generic radius rod /ladder bar setup [7/8" DOM tubing , heims on the front , clevis on the rear]

dave

 

How about the rear yoke, friend had a one that was bent somehow and when the u-bolt was tightened it deformed the cap and this led to a couple of quick failures before he found the problem. Also heard of the same results due the use of the wrong joint which had a different cap diameter.

 

Only 3 things I can think of are the aforementioned axle angle change under acceleration, a slight misalignment of the rear yoke in the driveshaft or that short of a shaft might need a constant velocity joint. 18k mile average isn't that bad. I've had some that didn't make it 5 miles but the problem was in my right foot.

 

You have a lot of change in angle in just for inches of movement from the rear axle. Larger, more robust Universal Joint will prolong the lifespan, but will still go away after a while.

Most universals are designed for less than 2º of angle change. At higher angles the less power the joints can transfer, so if you're on it and the suspension squats you could see 4-5-6º of angle on the joints, well past their effective range and outside of the torque transmission thresholds.

 

The wear shows on all 4 legs of the cross on the trust side, so I've kind of ruled out yoke derformation . AFA the short shaft, why just the rear joint & not both ??

dave

Joint number is NAPA 403

 

Did the math, if your suspension squats 2" that puts the universal joints at 10+ degrees of angle.

Be happy you are getting that kind of mileage out of your U-joints!

 

WOW , that much !! Thanks guys, guess I'll Quit bitchin' .

dave

 

Thats exactly what I was thinkin.

I bet its like driving on Ice when you drop the hammer

 

What are the symptoms of the failures? Needles wearing into the cross or just going to hell in a hand basket prematurely? Or the cross breaking?

You do have the correct U joint for the yoke that the rear axle has ?

You probably have a 369 Joint at the trans but there are several different numbers that work with the Ford 8 inch rear and may be just enough off to cause problems especially if the joint is failing on the yoke side rather than the drive shaft side.

Going back and reading ElPaloko's comments he probably nailed it and if your rod was a jacked up 4x4 instead you would probably be congratulating yourself for getting 18k out of a U joint.

 

When you measured the pinion angle, was the weight of the car on all four wheels?

 

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wear, or the cross material is spalling and pitting?

 

Yea, The angles are at ride height, on the ground. Failure is bearings eating into the cross.

As per previous post ... NAPA 403

dave

 

I've seen that happen when the straps holding the caps were tightened too much.

puts kind of a cross hatch across the part the bearings spin on..just something else to think about.

 

Actually if you are getting a bunch of straight lines dented into the cross journals that normally is a sign of no angle and the needles are not moving as the joint rotates.

 

Yea , however that would only show wear on strapped crosses, this shows wear on all 4,[preesed in & strapped in]

dave

 

The wear lines are about 3-4 "bearing widths" wide.& "slanted" slightly.


dave

 

You sure the shaft rear yoke is clocked perfectly with the front one? And 90* to the tube? With angled wear I suspect a yoke alignement issue.

 

Yep, it's dead-on , fella that did my shaft was very meticulous!!

dave

 

Check it out: http://www.machineservice.com/technical-101/drive-shaft-failure-guides/universal-joint-failure/

 

I wonder if the way your u-joints are phased are causing early wear? On first gen Camaros, GM phased the u-joints 15 degrees of each other. GM did this to preload the driveshaft. The tranny driving yoke leads the rear driven joke, thus the driveshaft is always preloaded. Did GM do this to eliminate vibration to minimize wear? I had a driveshaft shortened and had the yokes phased 15 degrees of each other. The driveshaft shop didn't feel it was necessary, but said they knew GM did it at one time.

 

Thanks , Elpolacko, As per the pictures, it appears I'm experiencing "brinelling caused by torque!! That I can live with.

dave

 

A few extras, the steeper the angle the less life expectancy from the u-joint.

 

I've been there....

does it look anything like these pictures?

http://www.jalopyjournal.com/forum/showthread.php?t=378968

if so, go to the end of the thread.

 

The rear is where the angle is changing. What does the guy who made the driveshaft say? They usually only put a constant velocity setup on one end of the shaft.

 

Sadly , the guy who built the driveshaft passed , rear is a single joint & the angle changes at the front also??

dave

 

Nope . the wear is "even" across 1 face of each cross.

dave

 

Look into either CV joints or double cardon u-joint. These are often found at 4x4 shops for jeeps, as when they are lifted very high their angles become extreme and also have short shaft issues. A double cardon has essentially two ujoints back to back.
Also, is it possible to lessen your initial static driveline angles by raising/lowering engine/trans and rear axle in order o give you more angle to play with when your suspension travels?

 

Since I have worked extensively in the 4x4 world, choosing a CV style shaft was a natural choice for my driveshaft-up Model A. I have a fixed yoke in my T56, where the CV assembly resides. The slip splines are in the shaft itself. Works like a charm, in the A, and both ends of my 4x4 rig.