Help diagnose this problem

[SamD]

I have a completely stock 1975 with a C4 with only 30K miles. Frequently as I am coming to a stop, there is a "Thump" that I can feel and hear that seems to be coming from the rear. Does this sound familiar to anyone?

sam

 

[twisted 66]

Check your axle u bolts, driveshaft bolts to make sure they are tight then look at your springs and brake mounting bolts...

 

[SamD]

Just went out and checked, and the Axle u-bolts, driveshaft bolts and break mounting bolts are all tight. The only thing that looks off is the small leaf on the passenger side is splayed a bit, and the upper shock rubber bushing is coming apart and the shock is slightly loose.

Sam

 

[Rustytruck]

Pull the rear driveshaft and check the u-joints and center bearing in the cv joint. While the shaft is out lock the hubs and drive the truck on the front end in 4wd. See if it was rearend related or drave shaft related. Check the slip yolk on the driveshaft. Make sure its greased and slips easily. I would also check motor mounts and transmission mounts. I would check the leaf spring and shock bushings.

 

[No Hay]

I had "thumps" too on my '76 with C4. I could feel it in my feet. I had my CV and U joints replaced and now smooth as ever.

 

[B RON CO]

Hi, as mentioned check the U joints. It could very well be that shock bushing. if it is not time for new shocks sometimes the bushings are replaceable. I would remove the shock and take it around the block. Good luck

 

[SHX669]

What they said but also check the driveline "slipjoint " when that gets worn the driveline can flex more up and down.
The CV joint is the #1 cause of vibration , noise etc in the drivetrain. It was the #1 warranty issue with EBs - due to lack of lube/maintenance . Some people didn't know it was there , some thought it was too much trouble to grease . A better idea for the CV is on my - Gee I Wish list.

 

[SamD]

New Bilstein shocks and a drive shaft rebuild kit are on the way. They were on my list anyway, so I just moved them to the top of the list.

Sam

 

[MarsChariot]

I had a vague "thump" in our '76 with C4 that I could feel in my feet, too. The drive shaft, CV, and U-joints were new. Turned out to be the nut on the drivers side of the rear engine-T-case mount was totally loose letting the drive train lift up and drop down on that side ever so slightly.

 

[Big Fish]

I have a completely stock 1975 with a C4 with only 30K miles. Frequently as I am coming to a stop, there is a "Thump" that I can feel and hear that seems to be coming from the rear. Does this sound familiar to anyone?

sam

My guess is the trans. Mine started doing the same thing when coming to a stop and at times sitting at red light it would get a bump after I was stopped

 

[LouisT]

On my '67, it was the slip joint as said here. During a stop it would slid open just a bit and then on acceleration the joint needed to close but the joint was worn and would pop because it couldn't slide smoothly. At the time, back in the early 80's I was told by other Bronco owners it was a fairly common problem.

 

[broncobilly72]

My 72 would make a bump noise on hard stops. I guess they used to call it axel wrap. Anyway everything looked good but I went ahead and installed traction bars and the bump went away.