tomseal6

2004 ZO6

When driving straight and mostly when turning slow, there is a bad clunk in my rear end and I dont know where to start to diagnose this.

It has always did this when i turned but now when driving straight?

55,000 miles

Eddie 70

There have been several fixes for this I have read about.

One is removing the axle nut and packing the splines for the half shafts with water proof grease and torquing the axle nut back into place.

Another was the pressure release flap located in the rear of the car closing after being lifted. This flap is thin rubber flap that opens when you close the door on the car and releases the pressure in the car.

One thing I found with mine was the floor flexing and making the bump sound when turning into my driveway. I found this by accident when vacuuming out my car. The wall right behind the drivers side seat when pushed on flexes enough that it allows it to make this bump noise. I read about a fix that I want to try just have not gotten around to it yet. It involves a flat piece of aluminum stock and gluing it to the flat wall behind the seat.

tomseal6

I was thinking about doing the axle shaft service on Monday and changing the differential fluid.

Can I just add fresh 75/90 gear oil from the drum and go?

Numb

The rear diff takes 75/90, but you also need a limited slip additive. You can buy the additive from the dealer, or many of the better synthetics have it already, such as Mobil 1, Royal Purple, Amzoil, etc.

tomseal6

did eaxctly what you told me to do. It pretty much got rid of the problem.

I only get a slight clunk when I shift gears or when I snap the gas pedal after coasting. I think I need to do that axle grease service.

tomseal6

I used a full synthetic 75/90 and a 4oz bottle of friction modifier. After driving for a day, I cannot hear a thing in the rear. I cant get over how quiet the rear end is now


Thank you so much CF You guys are always a ton of help I cant find anywhere else.

Z06forGM

Your axle nuts need to be tightened. 99% of the ones i worked on had nuts that backed off. We never had to add the grease, but i suppose it can't hurt.

tomseal6

What is the torque spec on these axle nuts?

Numb

118 ft lbs. I would loosen them up , clean up the threads with some penetrating oil, and and torque back down. If they have never been off, plan on eating your wheaties that morning. I had to extend my 18" breaker bar with an 18" piece of steel pipe to break mine loose the first time.

IPS Motorsports

Have you inspected the mounts for the differential as well?

The axles typically will not make noise (especially clunking) going in a straight line.

Brandon

tomseal6

After driving the car for the last week, I have not been able to hear anything. The noise is completely gone.

All I did was put that full synthetic PX3 fluid in the rear end with the 4 oz additive and it has been working great. The car is very quiet now so I dont think I want to fix anything else thats not broke. If it makes noise again in the future I will do check everything out again but I did not see anything worn out in the rear when I changed the gear lube.