Propeller Shaft U-Joint Vibration...again (1 Viewer)

[bajaphile]

Symptom: At highway speeds (55 mph+) when letting off the gas to coast, strong hum and vibration coming from u-joints on rear drive shaft.

I personally replaced both U-joints 1 year ago, probably 8k miles on them. The vibration went away until about a month ago. Now getting worse. When I pump grease in, the vibes go away for maybe 50 miles at most, and then come back.

I have Slee upper adjustable control arms and have set pinion at 0° to match output flange of x-fer case. I've played around with different settings +/- 2° and no effect.

Did I mess up the installation, or what? Anyone else have this problem? Advice?

 

[baldilocks]

What is the operating angle of the shaft itself? Once this angle is more than 6-7 degrees, Ujoints are under more and more stress as the operating angle increases and small imperfections are amplified. In short, joints won't last as long and achieving a smooth running driveline is more and more difficult. My Slee heavy 4" rear springs forced me into a DC rear shaft a couple years ago. No amount of pinion angle adjustment would make the shaft run smoothly at all times with an operating of 12.9 degrees.

 

[inkpot]

Is your slip joint getting loose? If so, then fresh grease will get thrown out pretty fast

 

[69LC]

When you replaced the joints, did you happen to pull the slip yoke apart? If you did, did you then ensure the end yokes were properly phased?

 

[bajaphile]

What is the operating angle of the shaft itself? Once this angle is more than 6-7 degrees, Ujoints are under more and more stress as the operating angle increases and small imperfections are amplified. In short, joints won't last as long and achieving a smooth running driveline is more and more difficult. My Slee heavy 4" rear springs forced me into a DC rear shaft a couple years ago. No amount of pinion angle adjustment would make the shaft run smoothly at all times with an operating of 12.9 degrees.

Hmm interesting. I haven't measured the drive shaft itself. I didn't realize anyone was requiring a DC rear shaft... Hmm. I'll have to check that out. Anyone else running one? I know its a common issue with these rigs, but I don't feel like I'm running any crazy amount of rear lift compared to others I've seen.

Is your slip joint getting loose? If so, then fresh grease will get thrown out pretty fast

I'm not sure.... when you say loose, do you mean axial, or rotational between the two splined parts?

When you replaced the joints, did you happen to pull the slip yoke apart? If you did, did you then ensure the end yokes were properly phased?

Yes, I made sure they were in phase. I marked, checked, etc. That was my first thought, but, the vibes had gone away and now have come back.

 

[baldilocks]

I’d be willing to bet the operating angkenofnyour rear driveline is at least 10 degrees. Even if the companion flanges are dead parallel, the more extreme angle causes exaggerated oscillation of the joint. It has to travel a greater distance n the same period of time. Stress is increased and joints wear out more quickly. The rather short length of the 80 rear driveline doesn’t help us out at all.

I had the same exact grrrrr... sound on declaration.

 

[landtank]

at 4" lift you should be able to get the truck to run clean. Besides the splines on the rear shaft what have you done to the front for caster?

There have been a few cases where people have had vibs with both shafts but when either the front or rear is removed they are fine.

I personally prefer to lengthen the lower control arms in the rear when addressing pinion angle as this takes some angle out of the drive shaft by increasing the distance between the t-case and diff.

I'd pull the front shaft and see if the vib goes away.

 

[baldilocks]

Another thought is the possibility of worn contol arm bushings allowing the pinion to deflect downward more than normal under deceleration increasing the angle in the rear most Ujoint under deceleration. Pinion deflection will happen no matter what under deceleration but worn bushings would exaggerate it.

The cheapest thing to do is to throw a new set of Matsuba joints in it and see what happens. I’m willing to bet your vibe will be gone at least for another 8,000 miles unless the problem happens to be bad bushings.

I’m also going to bet that, with the springs you have, especially when unloaded, your rig is lifted more than 4”.

 

[69LC]

Maybe also check your tcase outputs and pinions for bearing slop.

 

[jonheld]

when you say loose, do you mean axial, or rotational between the two splined parts?

There should be no axial play (zero) in a slip yolk. Any play will show as vibration when coasting (no load) as the 2 halves flop around.

 

[lcwizard]

did you also replace the front u-joints? If so, the front slip in indexed 90 degs out of what we assume is in phase from the factory. If you indexed it as most driveline shops would do ( in phase ) it won''t run smooth. Every time I send a front 80 shaft in the driveshaft shops assemble it
conventionally so I have to clock it 90 once I leave their sight....or they throw a fit

 

[bajaphile]

OK well it looks like I'll have to pull the shaft off and start inspecting. Like I said, if I pump the rear U-joint at diff with grease, it will go away...making me think it is related to that U-joint, but could be just masking a different problem.

I want to ensure I don't have any play in either the output flange of the x-fer case, as well as the pinion flange on the rear diff. I just had Zuk do my 4.88 gears in December, so hopefully the pinion isn't loose or damaged.

@lcwizard nope, I did not mess with the front. I have a DC front shaft and no vibrations from there.

 

[baldilocks]

Measure the shaft operating angle before you remove it. This angle is pertinent info for when you resurrect this thread a few thousand miles down the road to report the same problem again.

 

[bajaphile]

Measure the shaft operating angle before you remove it. This angle is pertinent info for when you resurrect this thread a few thousand miles down the road to report the same problem again.

Ok .. Will do that first!