Cobra4B

I got tired of my rear pads squeeling so I replaced them w/ the AC Delco (OEM GM parts) ceramics I've had sitting on the workbench for a couple months and bled the brakes. While I had the car up I repalced the 75w90 Mobil 1 gear oil in the diff w/ 75w110 Severe Duty Amsoil. I wanted to see if it would change the slight diff whine I get w/ the 3.90 rear end.... it seems that it may have made it a tinge quieter, but nothing major. It's stil most prominent just over 60 mph when you back off the throttle to maintain a steady speed.

As for the brakes the pads were about 1/2 worn and nowhere close to the wear tabs. The rotors were/are fine with no unusual wear. They're the original rotors and now have 49,9XX miles on them (They still have the star washer bit that keeps the rotors tight to the hub while on the assembly line). The only thing I found amiss was that the rear caliper slide pins were pretty much dry. I re-greased all the slide pins and applied grease to all the points on the pads and fresh pad springs as specified by the instructions on the Delco box.

Took her out about 30 min ago for the shakedown and all is perfect... nice and quiet now. So being that the pads were not worn, what could have been causing the squeeling? They would squeel at normal brake pedal pressure. When using very light pressure they wouldn't squeel and when hitting the brakes really hard they wouldn't squeel. Basically you could hit the brakes lightly and ramp up the pressure until they'd squeel loudly and then if you kept going and really pressed hard they'd stop.

Any Ideas?

-Brian

PS - the pads were the original factory coupe/vert pads from 2003. They're less aggressive than the stock Z06 pads.

marlinspike

Not getting on them enough or bad application of anti-squeal paste. I guess it could also just be a pad that is made out of spec. If it's the first one, usually you can take care of it by re-bedding them. Go to an MB dealer and buy some MB-branded anti-squeal paste. It's the best one I've found. You can also look and see if anybody makes shims for your rear brake pads. The squeal is not the pad rubbing on the rotor, but rather the pad vibrating when it hits the rotor.

Cobra4B

I'll bet MB's "anti-squeel paste" is just silicone grease of some sort.... my new pads came with a packet of it in each box and instructions on where to apply it. I allready had caliper lube/grease so I actually followed the instructions this time and all is well.

I didn't know the squeel was the pad vibrating.... I'm sure that's why new pad springs and fresh lube fixed it. I'll bet I could re-install the old pads now and not have any issues. Oh well I wanted to install ceramics from the get go.... no dust

marlinspike

Well, yeah, I think all the anti-squeal pastes are the same basic thing, but different consistencies, etc. All I know is I have tried three different pastes (can't remember the brands, this was ~7 years ago) and the best one was the MB.

Cobra4B

I've never ever put any paste/grease/lube on brake pads until yesterday. In all my years of tracking my Z06 and many many many brake pad/rotor swaps I never used it. Never had squeeling either.

Anyway... thanks for the info, I had no idea the pad could vibrate within the caliper and make a squeeling noise.

marlinspike

You probably drive that thing like a bat out of hell, don't you? If I get on the brakes a lot, I can probably get away without using paste on the rear pads of my MB, but the factory specs using shims and paste in the rear...and you find out why fairly quickly if you drive gently. I think not getting them hot makes the surface rough and more prone to vibrate or something. Porsches are the same way, only at all 4 corners.

Cobra4B

Cool.... yeah the Z06 got driven hard when on track.... the convertible I have now is just a nice weather daily.

Fabrik8

Squealing is usually just pad vibration, some pad compounds are much worse than others. Basically they're rocking back and forth at some frequency as they repeatedly grab the rotor and then slip. The motion is actually a lot more complex than that, but that's the basic concept. Most of the noise is from the pad contacting the caliper.

Some pads come with soft materials on the backing plates to help stop squealing, which is a lot more permanent solution than the grease. Basically the whole purpose of all of those things is to damp the pad vibration. I've never had a hell of a lot of luck with the grease unless the squealing is very minor.

sleeperteg

if the pads aren't worn down to the wear markers that squeal to let you know to replace them..
sometimes the brake pad can be slightly loose in the caliper and vibrating, making a squeal.. try putting some of that brake pad anti-squeal grease on

sk8rmike

You can get some stuff called i think...Brake Quiet to spray on the back of the pads. It's in a spray can and it sprays out red like red spraypaint but dries very tacky. It helps a lot. Also, beveling the edges of the pads with a sander so the entire pad surface isn't flat helps quite a bit too.