Premature u joint failure

99 chevy suburban 4wd

i had replaced the rear (differential) u joint about 3 months ago and it failed, so i put another one on and it failed within 15 miles!

in both cases the first sign of failure was vibration at higher speeds (over 45 or so)

one of the bearings on the differential side failed in the first case, and at least one of the same bearings failed the latest time

the differential bearings are held by bolts and straps

what should i look for first?

over tightening?

deformed yoke ears?

bent drive shaft?

unbalanced drive shaft?

Is the suspension lifted? An increase in the shaft angle can shorted U-joint life.

Try this the next time the U-joint is replaced. Before reinstalling the driveshaft back into the transmission, lube up the splines on the slip yoke with some molydenum disulfide grease. There have been cases where the slip yokes on these vehicles have been known to bind. And if the driveshaft can’t slide along the slip yoke to compensate for the rear axle moving up and down, something else has got to give.


I was thinking the same thing, namely that something is “off” with the splined shaft. Was it lubricated prior to installation of either of the replacement u-joints? As Tester stated, if the driveshaft can’t move in and out via the splined part of the shaft, that can destroy a u-joint very quickly.

Another possibility is that the new U-joints are not being lubricated properly. Many have just enough grease to hold the needles in place and since new U-joints are generally provided with grease zerks the joint should be pumped full of grease after installation and before use.

Is it known that the new joints are being greased?

no, it is 100% stock

good idea! i should have thought of that, however i do not think it is the problem as the slip yoke was smooth and free on disassembly and reassembly, but will try it if i ever get the time to work on the thing!

yes, the replacement joints were fully greased after assembly

If the rear end is kind of low, you may have a perfectly straight pinion angle and that will cause annual U-joint failure. At 15 miles, there may be other problems. The differential input shaft may be loose.

the drive shaft has a noticeable angle, not sure how many degrees, i will look at the differential input shaft when i replace the u-joint which i will probably be doing today, do you know if i will be able to feel if there is excessive play?