"thunking" when let off on the brakes

[Steeveo]

I have a 98 extended cab 1500 z71 with 340,000 km. I have had the truck for 5 years and still love the rig. One thing that has annoyed me since I got it: When I come to a stop and then let my foot off the brake I get a thunk in the rear. It is almost like someone ran into the back of the truck and gave it a bump. I have checked everything and can only figure that it is my Dif wrapping around becauce of the rear springs being a little sloppy and the plastic bushings between the springs being worn out.

Anyone with any thoughts on this.

[hraney]

Have you checked the brakes? My 97 K3500 had a slight thunk (not "rear-ender" level, but noticeable). I pulled the drums and my axle seals were leaking. Once the shoes were soaked, they swelled and acted 3 kinds of goofy.
But it could still be the differential. An old Plymouth Fury I had in HS had what seemed to be 3-4 turns of slack in the rear diff.

[Steeveo]

Thanks for the input. Brakes? na, been thru two sets of rear brakes since I got the rig. They're not the problem. Now the Dif could be the problem. Never have taken it apart and it does have a little hum of noise from it.

[sixnickel]

One thing you want to check is the slip joint on the driveshaft. The splines wear in their normal running position, as you apply the brakes, the axle winds up the opposite direction and the pinion moves downward, pulling the spline out just a little bit to where the spline is not worn. When you release the brakes and add power the shaft moves back in and will bind on the spline in the worn area. Sometimes just pulling it out and greasing it will help. It might just be the nature of the beast.

Sixnickel

1999 K1500 Suburban
BD 40 HP computer
SS Diesel Air Intake
FSD Cooler

2000 K3500 SRW
SS Diesel Power Package
FSD Heat Sync

[Steeveo]

That is an easy one to try. I'll do that on my next day without rain or snow.

[94Mule]

Is the thunking getting louder & harder? This is the tell-tale sign of a rearend going bad. Too much play in the diff. Have the backlash checked by a mechanic.

[Steeveo]

This does kind of make sense. The diff in these have adjusters don't they? They only ones I have played with are the old Posi diffs with clutches and shims. If this is the problem I should likely change the bearings at the same time.