Diagnose this clunk/thump

[bluearmz]

Truck is 1987 GMC 2500 4WD / 14 bolt rear. Here's the issue. When taking off from a stop, and sometimes braking, especially downhill, I hear and feel a clunk/thump that sounds like it is coming from the passenger side rear end. It also happens when the rear wheel goes over speedbumps and low speeds. Also, if going down a rough road, where rear suspension is moving, you hear it as you hit little bumps.

It is not really a metal on metal clank... sort of a clunk/thump you can hear and feel too. Inspecting the rear, everything seems to be in order, and front end has got new ball joints and wheel bearings.

Is is maybe a rear shock? I tried that idea where you put leafspring clamps, cause sometimes movement will cause it, but no change. Also already took out and greased the driveshaft splines.

Any ideas?

 

[DoubleDingo]

Could be rear shocks. When I bought my truck it made so much noise the dogs didn't want to ride in it. It was annoying and embarrassing to go down the road with the truck making so much noise. I got under the bed and removed the spare tire hanger, that didn't help. Tightened the bed bolts, that didn't help because they were already tight. Checked the tailgate and rear bumper, nope not it. Finally got right under the shock area, grabbed the frame and started making the suspension bounce, voila! The upper shock mounts on each side were loose as a goose, and the shocks were not moving so I got new shocks, and made sure the top mounts were tight, no more noise, and the truck rode way smoother. I got lucky that holes weren't wollered out, but the upper shock mounts may be causing it.

 

[MadOgre]

Ya either that or a worn spring bushing but a worn spring bushing should be noticeable in that the suspension would float a little when cornering

 

[paulrunyon]

Also, check your motor mounts. I had the problem with my 87 1/2 ton... would only hear it at take-off and sometimes when turning left, my motor mounts were worn to the point that my y-pipe would just touch the transmission cross-member.

 

[bluearmz]

Thanks for the reply's... still trying to figure out this one. I pulled off the rear end cover last night, cause I could prob use a fluid change anyway. Gears look really good, maybe replaced recently by previous owner. Will jack up and inspect it more today.

 

[bluearmz]

Well, I inspected the gears yesterday and here's what I found. All the teeth look fine on all of them. The top spider gear though, does have some play in it, you can move it up and down like 2 milometers. If I grab the ring gear and shake, you can get a slight (very slight) movement at the right (passenger side) bearing. Not sure if this is normal though.

Not sure if this can cause the thump/clunk noise. Seems like very little play to cause it. I haven't checked motor and trans mounts yet.

 

[smoothandlow84]

I'm guessing rear shocks or leaf spring perch bushing. Possibly a u joint?

 

[MadOgre]

U joints will be noticed according to RPM