68 Camaro Rear Disc Brake & Differential Problem

[Judges4u]

Folks,

My friend's 68 has some issues with the rear disc brakes dragging with a differential clunking noise. Rear drums converted to disc brakes by former owner.

When turning the wheels to the right or left moving very slowly, or moving forward or backwards very slowly, the rear wheels drag in a pulsating manner and you can hear a loud metallic noise coming from the The 12 bolt differential. I thought perhaps the rotor(s) were warped.

I removed both wheels and inspected the disc brake conversion kit parts. I noticed the shims are mounted on the outer side of the caliper holding brackets vice the inside where the spacer grooves are for installing the shims (they look like Summit Racing brand kit brackets) so that is one problem where axles will have to be pulled and shims installed correctly. The three bolts that hold the caliper brackets to the axle tubes on each side were not torqued enough creating way too much movement in the calipers while depressing the brakes so I tightened to decrease about 75% of the play / slop. With wheels back on, the issue was still not solved. At higher speeds I didn't notice any differential wining or howling. I initially thought perhaps the former owner didn't add the posi-lube, maybe causing this rear brakes to pulsate / drag during slow movement and turning of the wheels and moving forward or backwards. I was also thinking badly warn axle bearings.

Any ideas what else may be causing the issue? I'll be pulling the axles this weekend.

Thanks in advance.

Jim

[big gear head]

Most of the time this type of problem is due to old oil. The clutches in the differential are not slipping smoothly and causing the noise that you are hearing. Many times simply changing the oil and using the correct GM limited slip oil additive will cure the problem. It may take about a week for the new oil to completely fix the problem, so give it little time.

While you have the brakes off you can do a simple check to see how much the clutches are worn in the differential. Pull and push on the axles and see how much they move in and out. If they move more than 1/16 inch then they need to be shimmed or replaced. If this has the Eaton Posi in it then most of the time shimming the clutches is all that is needed. If it has an Auburn then replacing the differential is the only way to fix it. Axle end play is important when using disc brakes. When the axles move in and out it pushes the caliper pistons in and can cause problems braking.

[earntaz]

Try the GM limited slip oil additive #88900330 to get rid of the chatter. After resolving your brake issue and refilling the diff with a quality lube (including additive), in a large empty parking lot and drive slowly in a number of figure "8's" ... do the same in reverse and if everything in mechanically sound, you should be good to go ... Good luck ... TAZ

[Judges4u]

BGH and Taz! The money I spent supporting this site was the best investment ever. SCR is the most informative of all the sites I belong to. Thanks Gents and happy holidays to you two and your families and all the members and staff on this site. Semper Fi, Goat