Whirring/moaning sound while decelerating

[RustyS]

Hi there, I've been lurking on the forums for a while but I finally decided to create an account and ask for your guys help.

Recently I've noticed a loud whirring/moaning sound coming from the front end while decelerating, typically around 35-45 mph. I've read a few threads on the 80-series forum and folks point out the differential/pinion as a possible culprit. Assuming this, I looked at the pinion/yolk interface and there is no observable play. Is it possible that the pinion preload has gone out of wack/pinion bearings worn? Or could worn carrier bearings allow for audible noise as well? Ultimately, I feel I would need to pull the third member to get a clue but Im no mechanics elbow.

My cruiser is a 97. 295,000 miles with stock suspension and I'm confident it hasn't had any differential work before.

Any thoughts are appreciated, thanks

 

[BILT4ME]

Hi there, I've been lurking on the forums for a while but I finally decided to create an account and ask for your guys help.

Recently I've noticed a loud whirring/moaning sound coming from the front end while decelerating, typically around 35-45 mph. I've read a few threads on the 80-series forum and folks point out the differential/pinion as a possible culprit. Assuming this, I looked at the pinion/yolk interface and there is no observable play. Is it possible that the pinion preload has gone out of wack/pinion bearings worn? Or could worn carrier bearings allow for audible noise as well? Ultimately, I feel I would need to pull the third member to get a clue but Im no mechanics elbow.

My cruiser is a 97. 295,000 miles with stock suspension and I'm confident it hasn't had any differential work before.

Any thoughts are appreciated, thanks

Welcome!

There are a number of things that this COULD be. Let's start with simple and cheap.

1) Check your differential fluid levels front and rear.
2) Check your U-Joints. Truck on level ground, in NEUTRAL, WHEELS CHOCKED, parking brake set. Grab each end of each drive shaft and check for play. Up, Down, forward and back, and rotational. There should be no play in these on the first four, but will be about 15° to 30° rotational (figure from about 12:00 to 2:00 max from one extreme to the other of the rotation.)
3) Check for drive shaft sideways wobble at the yoke. Are the splines worn enough to make the DS wobble side to side? While you're under here doing this, grease the U-Joints and the yokes. If you've never done this before, this could be your problem. If you don;t know how, do a search for greasing drive shafts or greasing U-Joints on this forum.
4) Look for leaks at the yoke on the front (and rear) differential. This COULD indicate severe pinion wear.
5) Check your transfer case oil level. This could also be the front or rear output haft of the transfer case.

Start with those, then post your results.

 

[RustyS]

Welcome!

There are a number of things that this COULD be. Let's start with simple and cheap.

1) Check your differential fluid levels front and rear.
2) Check your U-Joints. Truck on level ground, in NEUTRAL, WHEELS CHOCKED, parking brake set. Grab each end of each drive shaft and check for play. Up, Down, forward and back, and rotational. There should be no play in these on the first four, but will be about 15° to 30° rotational (figure from about 12:00 to 2:00 max from one extreme to the other of the rotation.)
3) Check for drive shaft sideways wobble at the yoke. Are the splines worn enough to make the DS wobble side to side? While you're under here doing this, grease the U-Joints and the yokes. If you've never done this before, this could be your problem. If you don;t know how, do a search for greasing drive shafts or greasing U-Joints on this forum.
4) Look for leaks at the yoke on the front (and rear) differential. This COULD indicate severe pinion wear.
5) Check your transfer case oil level. This could also be the front or rear output haft of the transfer case.

Start with those, then post your results.

Thank you for the detailed response!

I was looking at the drives shafts for play and everything felt tight. In addition theres no leaks at the difs or T-case. I will go ahead and grease U-joints and see if that dues the trick.

 

[White Sheep]

Thank you for the detailed response!

I was looking at the drives shafts for play and everything felt tight. In addition theres no leaks at the difs or T-case. I will go ahead and grease U-joints and see if that dues the trick.

Mine is making a noise at that sped when idle/touch the pedal. I changed the gears, but didnt do the trick. I think i narrowed it down to the U-joints. I have quite a bit of play in all of them.

 

[SUMMIT CRUISERS]

Drop the front driveshaft. Check the rotation of each UJoint on both of its axis. If not perfectly smooth replace. If one has a hard spot, that’s your problem. Can’t be tested unless you drop the driveshaft.

 

[BILT4ME]

Thank you for the detailed response!

I was looking at the drives shafts for play and everything felt tight. In addition theres no leaks at the difs or T-case. I will go ahead and grease U-joints and see if that dues the trick.

Did you check the DS with the transmission in N and wheels CHOCKED, or did you just slide under it with it in park?

 

[RustyS]

Did you check the DS with the transmission in N and wheels CHOCKED, or did you just slide under it with it in park?

It was in neutral and chalked

There was minor rotational movement of the drive shafts but looked to be within the 12:00-2:00 range you described.