The Differential Man Shop

   OK, Let's start as if you come to my shop. You say, I have a noise. I've had it in several shops and they say I need to replace the entire differential. I'll say to them, It's OK. Let's go for a spin. I always want the customer with me so I can show him what I'm doing and what's going on. I always end up saying, You hear that, that's you pinion bearings or axle bearings or something else. When I was 16, I was taught by my boss, never take anything apart until you first know what part is bad. Once you start tearing into it, it too late for diagnosing. 

   One more thing, When ever I'm disassembling a differential, I'm always looking, turning, feeling and listening. I'm always gathering clues. When I see enough of the same problem, especially with newer trucks or cars, then I know something is going on at the factory. It's not the customer's fault.     So let's get to it. 

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Pinion Noise:

Pinion noise will always start the minute the driveshaft starts turning. It's a constant whirling ( not grinding ) and gets louder as the vehicle speeds up. The noise doesn't change usually because the pinion bearings still have preload or tight. the bearings and/or races have pitting due to to much preload from the factory. 

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Carrier Bearing Noise.

( Non C-Clip Axles ) Or "bolt in" axle models. These are differentials that have axles with pressed on bearings and held in place using bolt on flanges. The Carrier bearings will make a lower rumble or whirling noise. If the carrier bearings are worn and loose their preload, they allow the carrier to mis-align and you'll get some gear whine. But the gear whine will change when you push and let off the gas. It will not change when you swerve  back and forth, left to right and back. 

( C-Clip Axles )  These Differentials have axles that are held in place using c-clips that are located between the side gears and cross pin. The Carrier bearings will also make a rumbling or whiling noise. If the carrier bearings are warn and become loose than the noise will change when you swerve left to right and back. 

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Whining or Gear Noise: If the noise starts at about 20 mph as stays consistent until you let off the gas. It's usually the gears are damaged on the power side, but good on the coast side. Or the Carrier is loose and is shifting. If the Gear oil hasn't been changed and is burnt or milky, the power side wear score and wear out causing a lot of metal in the oil. Bottom line, If the noise changes when you push and let off the gas, its in the gear area. 

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Turning Corners, Vibrating or Rumbling noise. ( Usually feel it )  

( Non Positraction Differential )  When turning corners, you hear rumbling or feel roughness. Worn out internals will cause the differential to have a lot of play ( turning pinion back and forth ) To Test, Turn the corner while you push the gas and brake so you can load it. The noise will be loader under load. 

( Positraction Differentials )  The noise is coming from the clutches. They are grinding against each other due to dirty, burnt or milky gear oil. More severe, the clutch material on the discs are worn away and the discs are metal on metal. I see a lot of this because the posi clutches are set up to tight and wear prematurely. Also, the metal particles in the oil. needs to be removed by changing the oil.