1992 HD81 Baselining Drivetrain: vibration and clunk (1 Viewer)

[phoenix60]

I have a 1992 HDJ81 that I purchased in Sept 2014. Have been driving it weekends mostly (10Kin a year) and slowly base lining the rig.

Symptoms:
The major complaint is a vibration at higher speeds (predictably,more noticeable when wife is riding along, lol). Also a noticeable clunk/vibe when acelerating through 70-80km/hr (45-50mph).

New variables:
Upgraded front brakes to 16" so put on 16" tires and wheels. They are pretty much new, maybe 15K on them. 255/85R16 BFG MT's. (Ride was great when they were on my 88HJ61, so I don't think that balance is a concern.)

Treatment:
Have drained and replaced fluids in front and rear diffs, transmission and transfer.
Removed rear drive shaft and replaced u joints.
Removed front drive shaft for test drive with CDL engaged. - Ride was noticeably smoother, I thought to myself, "what have I been putting up with, this is great!" Clunk/vibe at 70-80km/hr was still present.
Upon inspection one ujoint is stiff, but no play in them.

Plan:
Today I will do the u joints in front drive shaft and reinstall. I will keep same phase as current: Sleeve and shaft yokes are same alignment, and flange yokes are also same alignment so I believe that is 'in phase' CIIW. Front drive shaft yokes are (--) (--).

Or should I install out of phase as on post 93 80's?

I'll also look at the throttle cable adjustment and post back.

 

[OffGridOverland]

Checked for a bent rim?

Is the vibration in the steering wheel / pedals?
Or the seat?

 

[CRSHR]

A stiff u-joint would be a failing u-joint and will cause a vibration most notably on accel. Replace and retest like you are doing. I would eliminate one variable at a time. Put the driveshaft in the same way you took it out. Make sure you mark it before you replace the u-joints so it goes back in the same way. Good luck!

 

[phoenix60]

Thanks crshr, I like the one variable at a time idea. Ran into one snag, front DS Ujoints are smaller than the rear so I have to return and exchange on Monday for the right size. I adjusted the throttle cable and on first test it seems to be smoother through the 70-80 acceleration zone, got my fingers crossed that a quick easy adjustment has eliminated the clunk!

Edit: Nope. Drove it for an hour today. Acceleration clunk is still present. If I stomp on the throttle, its not there, but under normal driving it is

 

[phoenix60]

Checked for a bent rim?

Is the vibration in the steering wheel / pedals?
Or the seat?

That's a good question, I had never thought about. The clunky/vibe is felt through the seat, not through the steering wheel.

 

[phoenix60]

The chase continues... Swapped in another rear drive shaft. That made a difference so I got mine balanced (and straightened!). Still a bit of a vibe but 95% less than before. Also swapped fluids in tcase and both diffs, set preload and checked wheel bearings, extended diff breathers.

 

[canman]

I always find that cleaning out the slip yokes splines helps a lot every couple years with driveline "clunk". Sometimes greases builds up or gets "hard" over the years with gunk.