[MotorCityMadman]

:help

Changed my rear diff fluid today. Bought the truck 3 months ago and was concerned about the rear diff because that's what went on my 98 K1500($750 repair) before I stopped driving it, so I am now paranoid by differentials.

Replaced with Lucas 75W-90 synthetic(Hopefully I do not regret the synthetic)
Only expected amount of metal shavings on magnet
Only drained did not remove cover


Took it out seemed to be driving smoother, so I hit the gas really punched it out of a red light, and once I started rapid acceleration I could hear a chatter kind of like a cross between kicking up gravel on the undercarriage and a stun gun.

Had a friend stand next to it and confirm that it was coming from somewhere between the gas fill and the rear axle and he said it sounded almost identical on either side.

I am really hoping that I did not shatter anything in the differential, I am thinking U-joint? read another thread on here that said something about a clicking from a u-joint.

Really nervous about this especially since I start a new job tuesday and need the truck.

No noise under smooth accel conditions.

PLEASE HELP!!!

Truck is a 2007.5 LMM 3500HD LTZ ext cab long bed approx 145k miles

 

[rd05lly]

just under a hard pull from a stop it does... normal it is the rear locking up ... if it does all the time and over 30 mph ... not normal

 

[MotorCityMadman]

Anyone agree? can I stop pulling my hair out? Was too busy freaking out look at the speedo and on the road let off the gas as soon as I heard it.

The truck was unloaded but I was gunning it pretty good. soon as I let off it goes away.

You have to understand I'm a few weeks shy of 21 years old and I owe more on this truck than I make in a year. Something is bound to go horribly wrong. It's my first diesel, first truck bigger than a 1/2 ton. First truck with 4 wheel disc, and first truck that I can officially say is MINE

 

[rd05lly]

as long as it was not a peg leg you are good to go.. wait til the ice comes you will hear the clicking more then

 

[MotorCityMadman]

Just thought I would post the final solution. It did turn out to be a u-joint. Turned out to be the cause of both this noise and the whistling noise that I thought was rear brakes.

One of the four caps was completely seized to the point I couldn't even take it off after pressing it out. Replaced with a NAPA greasable for around $30 also ordered a spare since it was a special order item

 

[andrew24dub]

What was the whistling sound you wrote about? I have almost the exact same situation here but mine only chatters when accelerating hard and turning so far. I haven't tried just a straight pull to see if it'll do it.