Loud Thunk

[That Ol 720]

I have a 83 720 and everytime I go for a drive or drive it somewhere I always hear this loud clunk/thunk noise. I have no idea where or what it is, although it sounds like its coming from somewhere near the middle of the bed of the truck. Its really annoying and I need to fix it but im not shure exactly where to start. Any suggestions??

[banzai510(hainz)]

have you put the rear of the truck on jacks and wiggled stuff around.???? Got to make a effort first before we can respond.

Does a 720 have a carrier bearing?  check the u joints, shock. ect or put it in gear and shirt it and see /feel if still makes a cluck

[weldingrod]

Mine was a combination of the slider driveshaft joint and a worn rear end. Slider joint damage caused by rear end- installed spare diffy from parts truck so have a rebuildable rear end if anyone is interested. Does it clunk when applying throttle or releasing it? Other comment here about physically wiggling parts underneath a good place to start.

 

[datzenmike]

2wd had two piece driveshafts with carrier bearing, 4x4 had a much shorter driveshaft with a splined slip yoke. 

 

 

When does it clunk???

 

Step on the gas?

Steady speed?

Let off the gas?

Letting out the clutch after gear changes?

Bumpy roads? smooth roads?

Carrying a load, empty or either?

 

[That Ol 720]

21 hours ago, weldingrod said:

Mine was a combination of the slider driveshaft joint and a worn rear end. Slider joint damage caused by rear end- installed spare diffy from parts truck so have a rebuildable rear end if anyone is interested. Does it clunk when applying throttle or releasing it? Other comment here about physically wiggling parts underneath a good place to start.

 

Not really when I give it gas. But mostly bumpy roads, and sometimes going around turns. I'll starts paying attention to see if it does it while I give it gas or not

[weldingrod]

Sounds more like a suspension issue.

 

[paradime]

My guess is it's a loose shock mount, Could also be an exhaust bolt came off. 

[That Ol 720]

On 10/8/2021 at 11:01 AM, weldingrod said:

Sounds more like a suspension issue.

 

I may be wrong but I'm pretty shure we put in some new leaf springs about a year and a half ago. Could it be a loose U bolt or something down there??

[captain720]

You have to re-torque the u bolts after installing new ones at intervals. If you skip that step they come loose and your axle clunks around

[datzenmike]

Also tighten the front eyelet and the shackles with wheels on the ground.

 

Shake the exhaust pipe. Maybe hitting the body