Rear Axle Howl Under Load Only....14 Bolt

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So on my 1990 K1500 pick up with 14-Bolt, the rear end howls around 35MPH. It's at it's loudest at 35MPH. You can hear it at 30 and at 40, but before and after that, it's hardly audible.

The noise is only present when under acceleration. Not there when your foot is off the gas.

The noise as always been there since I purchased this truck a few years ago.

In an attempt to address the howl right after I purchased the truck, I had new pinion bearings installed (there was play at the snout), along with new spider gears (they had chipped teeth). Ring and Pinion gears looked real nice.

Axle was QUIET for 1000 miles. Then howl came back. Mechanic re-tightened pinion nut. Howl went away. Came back 500 miles later. Re-tightened nut again, went away for 500 miles.

He says you can't tight it anymore.

What could be causing this? Perhaps the axle housing has some wear in the casing, where the bearings fit? who knows how long the pinion bearings were bad.

Kinda upset that the this 14-Bolt is shot. Do I have anything to worry about? Should it be safe to drive. It's just a $2500 truck. I already spent $600 on the axle 18 months ago. I don't want to put a junk yard unit it, if this axle is safe, just annoying at time.

And one last thing....the axle won't howl at 35 when cold, but once warm, it does.

Any comments? Thoughts?
 
This may be normal for GM axles. I have a 2012 with 29000 miles and it started soon after my first oil change. Do a UOA to see if wear is normal.
 
You can't just "re-tighten" the pinion nut. You have to take the carrier out and make sure there's a proper amount of preload on the pinion bearings. If you try to "ball park" it as this mechanic did, you risk screwing up the pinion bearings. Which it seems is what happened to you.
 
Originally Posted By: exranger06
You can't just "re-tighten" the pinion nut. You have to take the carrier out and make sure there's a proper amount of preload on the pinion bearings. If you try to "ball park" it as this mechanic did, you risk screwing up the pinion bearings. Which it seems is what happened to you.


This

Whoever "fixed" it the first time didn't add enough preload so its only tight,and howling when load is applied. You ether have to live with it or replace the crown and pinion and have it installed properly.
 
On a 1985 S10 delivery vehicle,at about 80K miles the rear axle showed a lot of slack (manual trans),when it was opened up it was shown as a blued ring gear (heated up) and 2-1/2 teeth chipped off.My take was the OEM GM fluid was too dilluted with other additives to aid the break in of the gears.At 80K the fluid was beat.The axle was buttoned up and driven until traded in....for a 92 S10 (mistake).I bought a new 89 S10 and at 10K I changed out the OEM fluid.Boy did it stink! Couldnt get near it while it drained.Of course I unloaded the truck at 29K miles as it was falling apart....my last GM vehicle.
 
The diff shouldn't howl if setup correctly. Agree with exranger06 regarding pinion preload. There is a crush sleeve in there that must be crushed just enough to create the proper pinion bearing preload. Over tightening the pinion nut will likely create too much preload. I would take your truck to another mechanic, maybe a place that specializes in 4X4's because they setup many, many differentials.
 
Take it to someone that knows what they are doing. I used a 4x4 shop that does gear changes almost everyday. I know for a fact that you just don't keep tightening the pinion nut. He might have done more damage then good.
 
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