Help Driveline Gurus!

On Monday I experienced a harsh vibration in the rearend that I thought was a tire going flat. It went away as soon as I pulled off the road and I took a trip back home (150 miles) without any problem. Yesterday at lunchtime I went out, got onto a nearby highway to go home for lunch and the vibration started again, Really bad too. Just as if I was doing 60 on the rumble strip on the side of the road. I called work and told them I was broke down and took the rest of the day to fix it. I went home jacked up the rearend, wiggled the U joints and everything seemed fine. It was due for a transmission fluid change so I did that, and noticed the the filter came out with the pan, so it must have been loose. Thinking that was my problem, I buttoned it back up with Motorcraft fluid and a Motorcarft filter. Took it for a ride and put about 50 miles on it. Truck ran as smooth as silk.

This morning the vibration came back, but not as bad. Here is what I noticed:

1) Vibration is definately coming from the rear

2) Speedmeter moves a little back and forth when it vibrates

3) The rear U-joint is very smooth and tight, no slack. I bought a replacement just in case but didn't put it in.

4) The output shaft of the transfer-case is a little loose, but seems an acceptable amount for a slip yoke. I took the drive shaft off of the rearend and cycled the output shaft yoke in and out and couldn't find any sign of unacceptable wear or slack.

Could this be a tire issue? These are the original POS Goodyear RTS tires and they have been rotated from the front to the back.
Could one of the belts be slipping or maybe just out of balance. I run them all at 40 psi ( 35 max on the sidewall) for better gas mileage. Could I have damaged them? Any and all answers are appreciated. Thanks!

 

Crashz,

At what speed did the vibration occure? Was it on acceleration or coasting or at a set speed?

Regards

Jean Marc Chartier

 

This reminds me of an emergency cable that locked-up on the right rear on my 1979, F-150. My vibration would go away after I stopped the vehicle and backed-up and foward a few times.

Also had a severe vibration when one of the upper rear shock mounts broke!

 

The vibration would come and go at any speeds higher than 45 mph and regardless of coasting, accelerating, or deccelerating.

Found a small chunk of metal on the right rear tire which is my lead suspect so far. I put my spare on and have felt it only once (very mild vibration this time), which could be just a road variation. I took it for a run last night and pushed up to 90 mph without any troubles, so (knock on wood) i think the problem is cured.

My emphasis on these tires are only because they have 60,000 miles on them, much of which I have run a few psi over the max, and New England is the pothole capital of the world. It wouldn't surprise me if all 4 tires are out of whack, but just the same that vibration had me panic-ing a little.

If you think I should watch out for something else, please let me know. I'll have my eyes peeled for the next few weeks watch ing everthing it does. Thanks guys

Leo

 

Scratch that last post-

Just got out on the highway at lunchtime (again!) and the vibration came on while going 70. I pulled to the far right lane, slowed to 50, still kept vibrating. Accelerated and kept vibrating. And after about a minute or two, it slowly got better and went away.

Now no dash lights came on but check this out. As I was accelerating / deccelerating the speedmeter didn't move in a smooth manner but jumped in 5mph increments.


Hmmm......

 

Crashz,

Check the oil level in the T-Case. The 4x4s take the vehicle speed info from the T-Case. Also check the slip yoke. If you play off road at all it gets dirty and may need a bit of grease. You have to remove the Drive shaft to get the slip yoke off. Make sure you index the shaft so you put it back on the same way.

JMC

 

I would drain T/Case & examine lube and magnetic drain plug. Speedo fluctuation leads me to believe transfer case (as JMC had indicated).

 

Thanks JMC and gearmanx17,

I hadn't thought of the transfer case. I'll check it out tonight when I get home. Thanks again and I'll keep everyone posted!

 

After a couple days of seemlessly smooth operation, the vibration came back last night on the way home from work. It got really bad as I slowed down. So I finally dropped the rear driveshaft the inspect the constant velocity joint at the tranfercase side.

What do ya know? It seemed tight, but would seize solid if you tried to move it. Felt like the a needle bearing was screwed up and locking up the joint.

So I took the driveshaft down to a machine shop to have the double U joint rebuilt. $165, but well worth the money for greasable U joints! I'll reinstall it tonight and see how she runs!