Trying to track down a major source of vibration and knocking sound coming from my Jeep ... seems to be dead center of jeep near the front of rear drive shaft.

I thought it might be related to my exhaust system -- as it was very loose, but I bolted it down tightly and made no difference.

The knocking sound picks up with RPMs until I get to highway speeds - then it disappears. And increases with engine RPMs from a stand still ... pushing in clutch makes it go away.

I got under and pulled the entire rear drive line to examine U-joints ... replaced one that looked a bit worn (rear one near rear axle) ... but made no difference.

Its a Tom Woods drive shaft along with SYE ... but the Woods shaft U-Joints still look good, although when disconnected the elbow seemed to stick a little when moving it by hand but I greased it up good and put back together.

It made 0% difference on the sound ... in fact now that muffler is secured its more noticeable and sounds almost like a U joint about ready to explode.

But its metallic clunking sound, like the drive-line is hitting the muffler on each rotation or such (its not).

Any ideas how to further troubleshoot this ?

Could it be that front elbow on the woods drive shaft ?
Or possible issues with the transmission or transfer case itself ?
Maybe a broken mount somewhere ?

specs:
1992 jeep cherokee sport (4.0l)
5 speed manual transmission
after market exhaust (cat back)
firepower ignition system
SYE kit
Tom Woods replacement drive shaft (~3 years old)

so far:
* pulled drive-shaft and inspected
* replaced rear U-joint on rear drive shaft
* greased everything possible
* secured exhaust system to stock mount points

 

no suggestions ?? Considering taking to local tranny shop and see if they have any idea -

 

I would guess maybe in the clutch pressure plate?you say it goes away when clutch is pushed? which stops the plate from spinning. thats a good one u have!! kinda tricky...

 

I removed the rear drive line and took it for a ride - and the noise disappeared.

After inspecting the driveline more closely, it appears the forward ujoint + ball + ujoint setup was binding.

The ujoints has zircs for greasing, but the ball itself was dry and damaged ... sent the entire thing back to Tom Woods custom drive shafts for repairs.

[edit]
Just got it back today, they had to replace the ball and all u-joints ... but drive shaft was still good.

Putting it back on today, will post if that resolved it 100% or not.