U-Joint or Rear End Noise?

1997 Chevy K1500 350 4x4 Extended Cab short box 100,000 miles.

While driving in town 30mph or less with the window down you can hear a low whoomp whoomp whoomp. Then while driving higher speeds of 45+ on the highway and all the windows up you can hear sort of a high pitched sound that changes pitches with vehicle speed. It sounds almost like a whistle you would hear if you were driving a car with a chunk of weather stripping missing.

The sound is barely noticable. In fact, I doubt I could capture it on a video or sound clip. I would rather get it repaired before I rip my rear end apart.

Does anyone have any ideas? The u-joints are original, but to me it does not sound like a bad u-joint. The rear differential is full and so is the transfir case. I think maybe I'll pull the differential cover off and see what I can see.

Thanks for any insight!

Check for signs of rust coming out of the U joint cups.Also unbolt it and check the u joints for binding.

Does the noise stay the same or change depending on whether you are accelerating or coasting? I have almost the exact same truck, but it is a 1997 with 194,000 and mine whines while applying throttle. I am assuming the rear end is just getting worn out and hoping she will run another 50,000 or so!!

If nothing else, just turn the radio up louder!! :smokin:

The high-pitched sound that changes pitch with speed is usually associated with the differential. If it's been a while between diff fluid changes, drain it and check inside the pumpkin for significant metallic residue. Also look at the ring and helical gear wear patterns as well as excessive slop. Good luck!

Copy, thanks guys!

When I have a chance I am going to yank it apart and see what I have. I checked the fluid because I thought maybe it is just low. Well, when I pulled the plug out, it started to come out so I assumed its got enough.

Right now it is to the point of being just an annoyance more than anything. If nothing else I'll probably just drive with it like that for the winter and save up and get the rear end rebuilt. How much do you think it would cost to have a shop install all new carrier, pinion, and axel bearings and seals, and adjust the shims? Shouldn't be any more than a few hundered. If I had a lift in my garage I would do it myself.

One more question, Is there a special wrench to take off the u-joint bolts to get the driveshaft out? I dont want to round off a bolt (a guy did that in the shop one time and had to cut it out and install a new pinion). Should I try and find a 6 sided wrench to avoid rounding them off?

One more question, if I were to replace the u-joints with greasable ones, what brand should I go with? Ac-delco?

Thanks!

~Tim

Looks like I need a new rear end, or a rebuild. Does anyone know how much a rebuild is going to run me? I realize it is depending on exactly what all needs replacing, but it cant be any more than a few hundred can it?

No idea on costs, but I'd guess that replacing the guts versus installing a salvaged rear would be about same. You'll have to call around to see what quotes you get. Just be sure that if you go used, make sure the ratios are the same as your front diff or you will kill the TC. Best way is to get the RPO code from the glovebox (probably G80) and ask the counter salesperson to find a donor match.

It may be time-consuming but you might try changing the fluid, especially if it has been a long time, you've gone through deep water, or the last time you filled it with a synthetic gear lube. Use regular non-synthetic lube and check your owner's manual for the need for any "friction modifier" additive (doubt it, but always check).

As for the "whoomp-whoomp" sound, that may be a tire out of balance or irregularly worn, or the rear shocks could be shot. Swap the front and rear tires to see if the noise source changes.

Good luck!

Sounds good! I've got 3.73's, checked the original window sticker. I have been recommended to this one shop that specializes in differentials and manual transmissions by two different people, so I called him today. He said he would call me back on monday and see when they can schedule it in. He said its common for the left carrier bearing to go out which causes the whole carrier assemply to shift left slightly and increase the distance between the ring and pinion gears. Sounds like a possibility to me. Either way I'll let him yank it apart and see what he thinks.

You dont like synthetic 80/90 gear lube? Glad you told me before I went and put it in because I probably would have.

Follow up!

Replacement of the carrier bearings fixed the issue! Exactly what I wrote above is what happened. No more sound, and best of all the clunk when going from R to D or vice versa is gone!