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242HD heavy clunk/thump over speed bumps

3K views 23 replies 7 participants last post by  Bigrigr 
#1 ·
Every time the rear end compresses over things like speed bumps and gutters in the road I can hear and feel a heavy thump/clunk in the center of the jeep.
All suspension parts are new and bolts re-tightened. Shocks new. U-joints new. Steering and axle parts checked.

Anyone ever experience this? It seems like every time the slip yoke compresses/extends I get a clunk. I've greased the slip yoke, no change.
Today I'll remove the rear driveshaft, cap the hole, and drive over a speed bump in FWD to see if it does it. Ill post the update.

Update: drove without the rear driveshaft, tc rear out capped, and 4hi. No thump at all. Definetly TC slip yoke related somehow.

SOLVED - See below
 
#3 ·
I've replaced the rear arms with the IRO kit. No longer have a ball joint back there. But yeah that would have been my first thing to check as I have experienced that before. Note that this thud/clunk is much more pronounced than when a rear ball joint knocks.
 
#7 ·
Update. Still having this issue and seems to be getting worse. Problem goes away with the rear ds removed. Getting concerned its gonna cause some more serious damage if i let it continue. Planning to replace the output bearing with a tight tolerance bearing to see if that helps or changes anything. Asking for a friend.
 
#8 ·
I get a thump/clunk in mine when i first back out of the driveway.(sounds like someone smacking the floor under the front seats-just one time) Nearly every time, but almost never get any noises going over speed bumps or trail riding. Its enough to make me notice, but never made me wanna tear into the Jeep to find it. I recently found that my initial 242HD swap had a stretched chain. It would grind badly in 4low on steep climbs. I swapped out that 242 for another, and stopped my other noises and general looseness in the drivetrain, but the thump is still there. I was hoping it was going to be fixed, but no go... I have new motor and trans mounts, and new bushings/balljoint in the rear upper control arm. Rear Lower control arms are tight and the bushings in good shape. Front upper control arms are new Core 4x4 adjustables, and the front lower control arms are upgraded with the lift with offset brackets at the frame. Im about to think its something to do with the exhaust. Mine HAD a 3" catback exhaust installed with a flowmaster muffler until I folded the T-pipe into a pretzel the other day while trying to navigate a steep rock wall. I had to cut the t-pipe off to get the engine to breath, and so far I have just added a short downturn tip to the back of the muffler to blow the hot air on the ground in front of the rear axle. I havent driven it much since i did this, but I dont remember it thumping the last time I drove it. And I do remember seeing a shiny spot on the top of the t-pipe where it went over the rear axle( it was just Kissing the floor) when i cut it off....Are you positive it isnt the exhaust hitting something? There is only one hanger after the trans mount. And its clear in the back next to the fuel tank...I know this doesnt jive with your removing the rear driveline, but just brainstorming here...
 
#20 ·
Just a thought about your clunk... Do you have an aftermarket crossmember? Have you checked on the trans mount? I had an issue with my trans mount bumping into the IRO crossmember when going from R to D and sometimes when going over washboard roads. The mount was new but its very flexible. My fix was the grind the crossmember down a bit where I saw contact between the mount and xmember.
 
#9 ·
Every time the rear end compresses over things like speed bumps and gutters in the road I can hear and feel a heavy thump/clunk in the center of the jeep.
All suspension parts are new and bolts re-tightened. Shocks new. U-joints new. Steering and axle parts checked.

Anyone ever experience this? It seems like every time the slip yoke compresses/extends I get a clunk. I've greased the slip yoke, no change.
Today I'll remove the rear driveshaft, cap the hole, and drive over a speed bump in FWD to see if it does it. Ill post the update.

Update: drove without the rear driveshaft, tc rear out capped, and 4hi. No thump at all. Definetly TC slip yoke related somehow.
Try lowering your tyre pressures.
We run 30psi in our lightly loaded 4.7 to reduce the thump over speed bumps.

We also get a quieter more comfortable ride, along with better road holding and steering at 30psi.
If I dropped the rear pressures a bit more, I'd get better road holding and steering.
But our insurers might not like it is they found out.
 
#10 ·
I used to get a noise in a similar fashion going over speed humps and braking - tracked it down to the insulation above the exhaust. It's a kind of aluminium sandwich affair and from what I can make out, due to vibrations it work hardens around the securing studs, then the holes open up and it moves around as you brake, accelerate and the like. Doesn't explain why it would stop with the rear driveshaft off, unless it was hitting the driveshaft?

I was getting a banging noise the other day and this was a broken clamp on the rear sway bar allowing the bar to move.

I have also just greased the slip yoke and the noise I was getting on braking has now disappeared. I used CV joint grease to do this.
 
#12 ·
DS u-joints are all new. Suspension is all new. Torque of everything was checked. I looked around of signs of metal-on-metal contact... I'll be installing a tight-tolerance bearing on the output soon to see if the axial play in the output bearing might be causing this.
 
#13 ·
How about you get a used rear driveshaft from a scrappers?

Then check the length of your shaft against the other shaft?

If the scrappers shaft is shorted than yours, use it.

If the scrappers shaft is the same length, cut say an 1/8th inch of the front end, and try it?
 
#14 ·
Problem solved with the following method for future reference in case anyone else has this issue. The cause of my issue was too much axial play between the tailcone, bearing, and snap ring. When the suspension compresses, the driveshaft pushes/pulls on the splined output shaft.

Replaced the rear output bearing with a tight-tolerance one from mcmaster (PN 6661K48).

Replaced the output snap ring with a shaft collar (PN 6063K23). I made sure the shaft collar was installed tight up against the bearing.

Sanded down the tailcone housing mount face so the bearing is more tightly clamped. I did this by spray gluing 240 grit sandpaper on my welding table and sanded it down by hand. Time consuming but the finish is nice and flat. You can test the depth by marking the outer bearing race and tailcone mount face with sharpie, slide the tailcone over (no bolts), and rotate it around. The areas where the tailcone contacts will wear away. I did this until the mount face barely touched and the bearing race had full contact.
 
#17 ·
This was with a stock d/shaft? I ask because I am rebuilding a 242hd this winter for mine but am going to a double cardan at the case.
 
#19 ·
Yup stock shaft with the original slip yoke.

Amazing solution to this problem. This is one that most would not take the time to dig this deep. I need to look closer at this myself. I dont always get this clunk, but every once in a while.....Thanks for the extra effort, and posting the solution here once you found it.
If it bothers me enough I go as deep as I need to lol. Its a pretty simple fix that reduces stress on the output bearing. I highly recommend doing it.
 
#18 ·
Amazing solution to this problem. This is one that most would not take the time to dig this deep. I need to look closer at this myself. I dont always get this clunk, but every once in a while.....Thanks for the extera effort, and posting the solution here once you found it.
 
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#24 ·
I have checked this trans mount situation a couple times, and one time i found a couple slightly lose bolts on the crossmember. I had apparantly not gotten them all the way tight when I swapped out the old trans mount. That was a few months ago, and honestly, I havent really heard it since.I am driving this Jeep every day now to get to work, and It doesnt seem to do it like it did. Maybe I got lucky...I am still running the factory crossmember.
 
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