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Old 01-18-2008, 12:00 AM   #1
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Default Strange Brake Noise

I'm running into some odd brake noise. Sometimes, when braking gradually downhill, I get a strange moaning noise from the rear brakes, but generally only around 10-30mph. It also happens occasionally when backing up. It doesn't sound like a normal brake groan, or squeak. It sounds more like the sound when you blow across an empty glass bottle, and almost doesn't feel like it is coming from the brakes.

The car is a 2005 SE, the brakes are all less than 15k old, and checked out okay the last time they were measured, about 5k ago. The rear brakes have squeaked a little from the day they were put on, were checked, and nothing was found wrong.

Any ideas?
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Old 01-18-2008, 12:31 AM   #2
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Mine do that too. There are plenty of tricks to keep brakes quiet. Everything can be mechanically sound and you can still get noise. Sometimes there are special pads to install behind the brake pads, or some goo to put on the back of the brake pad.

Usually the noise is just annoying and not a real safety issue. You say the brakes are fairly new and have been inspected so this is probably the case here.

I am putting up with mine until they need to be replaced anyway, then I will spend the effort to get them quiet.
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Old 01-18-2008, 10:24 AM   #3
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Hawkjet,

Thanks for the advice. I didn't figure it was a safety issue, but it sure is embarassing.
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Old 02-17-2008, 12:49 AM   #4
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so whats the fix here ?
my 92 does it really badly

the brakes work fine

really noisy hum/moan grab noise

especially when after sitting in high humidity and when cold

really bad

how do you fix this

what is the exact cause

is it the brake pad material face contact to rotor face ?

or the backside of the pads to the caliper and piston contact ?

and how/why ?


if its the pads doing it then what pads do you get that wont do this ?


thanks
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Old 02-17-2008, 12:02 PM   #5
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GM issued a TSB for that issue for the 2000 and 2001 model years, that should have been already applied to yours.
Quote:
Date: September, 2001

TECHNICAL
Subject:
Rear Brake Moan/Hum Noise During Brake Apply
(Replace Rear Disc Brake Pads)

Models:
2000-2001 Buick LeSabre, Park Avenue
1998-2000 Cadillac Seville
2000 Cadillac DeVille
2001 Oldsmobile Aurora
2000-2001 Pontiac Bonneville

Attention:
This repair DOES NOT apply to rear brake grunt/groan, pulsation or squeal.

This bulletin is being revised to add a model and to update the model years. Please discard Corporate Bulletin Number 00-05-23-001 (Section 05 - Brakes).

Condition

Some customers may comment on a moan type noise coming from the rear of the vehicle when applying the brakes. This condition may be more prevalent during city stop-and-go or mountainous driving situations. In rare cases, this moan type noise can also occur during the first or second application of the brakes when the brakes are cold.

As the vehicle slows down from 48 km/h to 0 km/h (30 mph to 0 mph), the rear moan type noise may produce a low resonating "hum".

Cause

This condition may be due to pad vibration being transmitted to the caliper assembly resulting in a low frequency resonance.

Correction

Replace the existing rear disc brake pads with a new rear disc brake pad service kit.

The new rear disc brake pads will reduce the vibration being transmitted to the caliper assembly.
There are several good brands of pads that could lessen the problem. They may have shims attached to the back, or have a special coating. Some will bevel the edges of the pads, and others may have a slit down the center to lessen the vibrations. If you want to try some new pads, go to a good auto parts store that has a knowledgeable person at the counter, or you could try some things on your own, with your current pads.

Buy some disc brake quiet, and apply it to the back of the pads, after cleaning them well. Also clean up the caliper piston. Clean up the metal pad clips well, and apply a touch of brake lube to them, as well as lubing the caliper bolts and pins well. You could also try filing down the side edges of the pads a touch, with a file.

A '92 has drum brakes in the rear, so is a totally different animal. Your best bet is to pull the drums, and inspect the brakes. Check the brake wheel cylinder for leakage, and look for any broken springs. If the cylinder is leaking, replace it, clean up the drum well, and replace the shoes. Also, make sure the brakes are adjusted properly. If you need additional help, that would be better posted in the 92-99 section.
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