whining under acceleration (gear sound from rear)

[GSLENK]

This whining is barely audible. It reminds me of the gear sound of reverse once you go over 10 mph. Sounds as if it is coming from the back. Becomes audible at around 20mph+ and only under load and at cruise with gas pedal pressed cruise. Under decel it is non existent.

It varies with speed and not engine rpm as far as I can tell.

I thinks its a differential issue. I cannot duplicate on jackstands, loading the engine with front and rear brakes isn't helping, (and is too crazy imo).

I poked around with a stethoscope, (a real one)...

-I hear a clunk in the diff on sharp acceleration (pedal jabs) with and without stethoscope, and I can hear it in the car.
-I do hear a gear noise in the diff but only with the stethoscope, it is otherwise drown out by my slightly rusty rear brakes noise (car sat a little)

-I can rotate the driveshaft about 10-30 degrees until the rear diff stops it. There is mo play in the drive shaft it self, no play in the axles.

-I recently switched to redline lightweight shockproof gear oil. I have heavy shockproof in the mail on its way, just to check.

The carrier bearing made no noise whatsoever even with the stethoscope.


Any ideas? anyone have this happen before?

 

[spyderdrifter]

How recent was your gear oil change and how discolored was the old oil?

 

[1slow03cobra]

pull the cover and run a pattern on it to see how the gears are riding

 

[GSLENK]

I swapped sub frames. then took advantage and changed fluid. it was OEM fluid. probably 22 years old and about 28 k miles old (yes 28 not 280).

Color was mostly grey towards the end. I guess half grey half yellow ish. no chunks. just a fine oily paste on the magnetic drain plug. I assume its metallic powder from "normal" wear.


So do I just pop the rear cover off and stare at it? I've never opened a diff or trans or anything like that.

 

[spyderdrifter]

To look inside, yes just take off the cover. But to really do much else, you'll need to take it apart. Not with all repairs, but most.

 

[bkiel]

Have you checked run out on the ring gear? Or clearanced the pinion/ring teeth? Pretty easy to do with right tools. Did this just start or has it always done this? Some rear-ends seem to hum when they are slightly loaded when cruising.

 

[GSLENK]

just started. could you point me in the direction of such a tutorial?

also, It does seem like there is a lot of play in the diff. I can grab the driveshaft, and rotate it about 20 degrees (about a 1/2 inch of the circumference) and it I can make it "clunk" at the extremes of each turn by hand.

 

[spyderdrifter]

Here's a start, hope it helps: Differential Measurements and Adjustments

That's basically what I did when I went through manual transmission and diff training. I'll look through all the power point stuff I was given during that class to see if it explains everything better. If so, I'll upload it here.