Whining noise from rear axle

[jkersenbr]

I've got a 2000 Dodge Dakota that is making a high-pitched whine from the rear axle. It's the "heavy duty" option 9" rear end WITHOUT limited slip. Has 96K miles on it and the fluid looks pretty clean. (I've only had the truck for the last 12K)

It starts as a slow whirring sound around 20MPH and increases to a whine at highway speed. The noise changes little with acceleration and deceleration.

It's made the noise to some extent as long as I had it. I just thought it was gear noise. But lately it's been getting worse.

I thought maybe I was mistaking tire noise, so put it up on jacks and ran the rear wheels off the ground...still does it.

What do you think? Are the ring and pinion toast? Or maybe just bearings?

 

[SparkyJJO]

I'd get the differential checked out. If it is getting worse that is not a good sign.

 

[iamwiz82]

Does it only occur on acceleration?

I would guess that it's a bearing by your description. You may as well have all of them replaced if the diff is disassembled.

 

[mrblotto]

U-Joints?

 

[jkersenbr]

Originally posted by: iamwiz82
Does it only occur on acceleration?

I would guess that it's a bearing by your description. You may as well have all of them replaced if the diff is disassembled.

No it does it both accelerating and decelerating. Also coasting, even in neutral.

Originally posted by: mrblotto
U-Joints?

The U-Joints are OK. I know what they sound like and this isn't it. They click, ping, and vibrate, they don't whine like a dying TV.

 

[Gillbot]

Bearing and/or gears. I've hears U-joints whine also.

 

[iamwiz82]

Originally posted by: jkersenbr

Originally posted by: iamwiz82
Does it only occur on acceleration?

I would guess that it's a bearing by your description. You may as well have all of them replaced if the diff is disassembled.

No it does it both accelerating and decelerating. Also coasting, even in neutral.

Sounds like bearings then. Gears normally only whine on accel or decel, though it is possible to have gears whine continuously. I have never seen that personally.

 

[woodie1]

"No it does it both accelerating and decelerating. Also coasting, even in neutral. "

That sure sounds like a bad bearing.

 

[mrblotto]

On a slightly related note (no hijack intended), I had the rear diff changed out of my very first new vehicle: an '88 Dodge Dakota. Anyhow, for some reason I guess the real mechanics were on vacation, because a 'higher gear' rear diff was installed. My speedo would say 50, but I was actually going 60. For a few days I thought I was just going crazy 'cause I would be driving down a hill and think 'man, it feels like i'm flying down the road.....' lol

/end hijack

 

[iamwiz82]

Originally posted by: mrblotto
On a slightly related note (no hijack intended), I had the rear diff changed out of my very first new vehicle: an '88 Dodge Dakota. Anyhow, for some reason I guess the real mechanics were on vacation, because a 'higher gear' rear diff was installed. My speedo would say 50, but I was actually going 60. For a few days I thought I was just going crazy 'cause I would be driving down a hill and think 'man, it feels like i'm flying down the road.....' lol

/end hijack

Impossible. Dakotas read the speed well before the differential.

 

[Gillbot]

Originally posted by: iamwiz82

Originally posted by: mrblotto
On a slightly related note (no hijack intended), I had the rear diff changed out of my very first new vehicle: an '88 Dodge Dakota. Anyhow, for some reason I guess the real mechanics were on vacation, because a 'higher gear' rear diff was installed. My speedo would say 50, but I was actually going 60. For a few days I thought I was just going crazy 'cause I would be driving down a hill and think 'man, it feels like i'm flying down the road.....' lol

/end hijack

Impossible. Dakotas read the speed well before the differential.

It doesn't matter where the speed is read as they are calibrated for a certain number of pulses per revolution. Unless you are taking speed on the rear wheel exactly, changing the gear ratio will alter the speedo unless calibrated for.

 

[funboy6942]

Bad bearing as suggested, or just change the diff fluid for it is low, and has been since you got the truck. The fluid can also leak into your drums so look at the tires on the insides for wetness, sign of diff leak, or brake fluid leak. But if the bearing or low, to noe, or very thin, worn oil will cause the moving sound you speak of.

Also I am not sure but does that truck us a split drive shaft? If so may want to check the bearing at the split as well.

 

[Demon-Xanth]

I don't know for sure about the '88 Dakota. But the '97 and up measure the speed off of the ring gear, so changing the gear ratio does NOT affect the speedometer calibration.

OP: for reference, your rear end is a Chrysler 9.25". You can verify this by looking at a small tag on the driver's side axle tube:
http://dodgetruckworld.tenmaga.../DemonXanth/306206.jpg
http://dodgetruckworld.tenmaga.../DemonXanth/306207.jpg (9.25" 3.55 "trac lock")

You'll need about two and a half quarts of fluid to replace your fluid, but it's a pretty easy job. You can check the fluid by simply removing the plug on the cover and sticking your finger in the hole. Also note that a possible culprit is the carrier bearing.

 

[iamwiz82]

Originally posted by: Gillbot

Originally posted by: iamwiz82

Originally posted by: mrblotto
On a slightly related note (no hijack intended), I had the rear diff changed out of my very first new vehicle: an '88 Dodge Dakota. Anyhow, for some reason I guess the real mechanics were on vacation, because a 'higher gear' rear diff was installed. My speedo would say 50, but I was actually going 60. For a few days I thought I was just going crazy 'cause I would be driving down a hill and think 'man, it feels like i'm flying down the road.....' lol

/end hijack

Impossible. Dakotas read the speed well before the differential.

It doesn't matter where the speed is read as they are calibrated for a certain number of pulses per revolution. Unless you are taking speed on the rear wheel exactly, changing the gear ratio will alter the speedo unless calibrated for.

I am an idiot and not sure why I posted that, because I know (and knew) you are right. My only excuse was is that I was tipsy at that point.

 

[Subbaculcha]

Originally posted by: iamwiz82

I am an idiot and not sure why I posted that, because I know (and knew) you are right. My only excuse was is that I was tipsy at that point.

Not necessarily...when I swapped gears on my 96 mustang gt, I had to change out the speedometer driven gear (at the transmission) to get my speedometer in sync with the new gears.

 

[bctbct]

I just had the same symptom on my 05 1500 and it was the pinion bearing. Mine was covered under drivetrain warranty.

 

[cardiac]

I think bctbct hit it on the head. Find a good transmission/differential shop and have them check it. They can replace the pinion bearings and new axle seals for about $300 or so.....

Bob

 

[bctbct]

Check warranty because mopar has many different age/mile restrictions.