Technical 7.5" GM 10-Bolt noise

I have a 7.5" 10 bolt out of an '84 S-10 behind a mildly built 355. It has lived happily for about 15 years but recently has developed a noise while driving. I did a little burnout one day and afterwards the rearend makes a "clang, clang, clang" noise at cruising speeds above 30mph and upon deceleration. It does not do it under acceleration. The noise seems to reverberate through the driveshaft. I have checked the carrier bearing and all the u-joints and even replaced the rear u-joint due to a little slop. I am not a differential expert. What could cause this noise? I am hoping against odds that maybe something has backed-off and just needs re-torqued. The operation of the rearend does not seem to be affected. It steels feels smooth with no jerking or lurching.

 

Older GM rearends tend to crack teeth on the pinion gear, then the teeth fall off. But there are other things that could be wrong, too. You probably need to open it up and take a look. 15 years is good service out of one of those little rears.

did you check the torque on the pinion nut when you had the driveshaft out?

 

I did not. Not sure of the process or the torque specs. I presume you mean the nut in the middle of the u-joint saddle on the pinion?

 

yeah, that one. The torque on the nut is supposed to be kind of high, but it helps if you understand how the crush sleeve (bearing spacer) works, and about pinion bearing preload, etc. If the nut is loose, you kind of need to take the rearend apart and fix things.

 

If your diff is broken and has metal debris , replace all bearings no matter what they look like.
And clean out the axel tubes, metal likes to hide in them

 

The bearings in those axles wear fairly quickly, I have one of those trucks with 260k on it and its on its second pinion bearing and third set of axle bearings. truck has never been loaded heavy or towed, I'd bet its an axle bearing

Dave

 

sounds about due for a total rebuild , for one they do not like to be abused and the center sections are known to break in half ( and will still move the vehicle ) that ussually is a clicking noise under power or turning, and also for spitting gear teeth .. , if you overhaul it inspect the axle ends as often the bearing area wears and pits , new better alloy axles are available cheaper than OEM .and use nothing but Timken or SKF bearings ..