Thump in drivetrain under load

[jnewkirk]

I'm having a problem with my 1998 1/2 2500 4x4 5 speed truck, and before I spend a lot of time troubleshooting I'm tapping the vast knowledge of y'all.



During heavy acceleration or heavy load there is a thump (you feel it rather than hear it). The transmission and transfer case shift levers jump when this occurs. It seems related to driveline torque rather than engine torque as it occurs at lighter throttle in lower gears.



It feels like something is binding and going over-center when torque is applied. Tomorrow I'm going to check the slip yokes on the driveline to make sure there is travel in them. Could be the driveline is bottoming out as the engine/transmission move from the torque.



Anyone know about this problem and have the fix.



John

 

[Crazy Horse]

If you have an C-cab or Q-cab you might be feeling the slop on the carrier bearing in the driveline, especially if the if you are low in the powerband when you are accelerating. I have felt what you are describing a few times in the floor boards between the seats. The only time I have felt it is when the camper has been in the bed and I have accelerated under high torque conditions. Mine has been like a thump, thump, thump. The carrier bearing is encompassed in rubber and it does do some moving when the driveshaft is moving. It wouldn't hurt to take a look at the u-joints and check the carrier bearing, but being a 98. 5 I wouldn't think there would be a problem with them. I don't know if this helps any but I think my situation is normal.

 

[jnewkirk]

I discovered I can simulate the problem by putting on the parking brake and slowly engaging the clutch in 1st gear. I had my wife simulate the problem while I looked underneath. I found that the slip yoke that slides into the transfer case was being shoved to a stop into the transfer case when the engine/trans twisted from the torque causing the driveline to push against the carrier bearing.



As to why this is happening, my calibrated eyeball tells me the carrier bearing mounting bracket is crooked where the bearing cage is welded to the bracket causing it to be tipped toward the transfer case. The carrier bearing bracket does not have any slots in the mounting holes for fore/aft adjustment, so I could'nt slide it to adjust the distance from transfer case to pilot bearing. I ended up slipping a washer under each of the forward mounting holes on the bracket to straighten the "tipped" condition. This moved the yoke about 3/8" out of the transfer case.



Problem is gone!



John

 

[David_VT]

same symptom post clutch job but no carrier bearing?

I've had these same clunks since having my clutch upgraded. Unfortunatly I have a QC shortbed which does not have the carrier bearing.



Anyone have a clue what else could be doing this? I've got a drivetrain wind up that is just awful.



Also I just noticed while backing a heavy trailer across a lawn in 4-lo that I am getting a cyclical sharp clunking from the front end.



The second problem is likely related to driving on dry pavement in 4wd by mistake. It is a sick expensive sound.

 

[Crazy Horse]

David the clunk in the front is curl hop and its normal in a 4wd when turning sharp. The tires are trying to roll under as they are turned side ways.

 

[David_VT]

Thx, I really had never heard it before and it scared me.