brake squeal (update)
05-13-2004, 12:12 AM
#1
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brake squeal (update)
those of you with long memories will remember that i've been chasing a squeal in the brakes of the chariot. the squeal occurs at about 80km/hr and up, and is noticable if you have the stereo off.
after determining that it was the rear brakes (handbrake application silenced the squeal), i got the dealer to fit new rear pads after de-glazing of the old ones didn't work effectively (squeal re-appeared after a few weeks). i pointed out that audi had superceded the old part number with a new one and suggested that this was because others had found the same problem.
now, the 1st day after the new rear pads were fitted and the rear rotors skimmed - the squeal is still there.
bugger....
symptoms:
1) squeal from about 80km/hr
2) disappears with a hard application of the handbrake.
3) with a very light application of the footbrake, the squeal sound will increase in volume noticeably and then disappear all together.
4) when cornering hard the squeal will disappear
the dealer is taking the car back and going to put a electronic sound monitor on the car to determine precisely where the sound is coming from.
my thoughts:
1) skimming the rear rotors should take any issues of out-of-round rotors.
2) glazed pads were not the cause
3) hubs?
4) front brakes - why the increase in sound when the footbrakes are operated and not when the handbrake is?
5) new pads should discount any issues around anti-rattle springs
any ideas?
after determining that it was the rear brakes (handbrake application silenced the squeal), i got the dealer to fit new rear pads after de-glazing of the old ones didn't work effectively (squeal re-appeared after a few weeks). i pointed out that audi had superceded the old part number with a new one and suggested that this was because others had found the same problem.
now, the 1st day after the new rear pads were fitted and the rear rotors skimmed - the squeal is still there.
bugger....
symptoms:
1) squeal from about 80km/hr
2) disappears with a hard application of the handbrake.
3) with a very light application of the footbrake, the squeal sound will increase in volume noticeably and then disappear all together.
4) when cornering hard the squeal will disappear
the dealer is taking the car back and going to put a electronic sound monitor on the car to determine precisely where the sound is coming from.
my thoughts:
1) skimming the rear rotors should take any issues of out-of-round rotors.
2) glazed pads were not the cause
3) hubs?
4) front brakes - why the increase in sound when the footbrakes are operated and not when the handbrake is?
5) new pads should discount any issues around anti-rattle springs
any ideas?
05-13-2004, 04:33 AM
#2
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Long rambling and thinking out loud ...
1. You said hard application of either the brake pedal or handbrake makes the squeal disappear. Light application of the brake pedal makes the squeal worse. You didn't say what happens with light application of the handbrake, but modulation would be difficult; let's assume that this would make the squeal worse.
2. De-glazed or new pads made the squeal disappear, if only for one day or a few weeks. The squeal returned sooner when the rotors were skimmed, and the pads would bed in sooner in this case also.
I'll guess that at least one of the rear pads is dragging ever so slightly, enough that even just hard cornering gets the pad off the rotor and makes the squeal disappear.
So a few questions:
Are the inside and outside rear pads on both sides wearing evenly?
Are all 4 rubber boots (at #6 in the pic) protecting the sliding pins of the rear caliper carriers intact?
Were these pins re-lubricated with brake caliper grease when the rotors were removed?
Do the pins fit snuggly in the carrier but slide in and out freely?
When the rotors were removed for turning, the caliper carriers also need to be removed. Even if the rubber boots are now installed correctly, one might have been off for a while, allowing water in alongside the pin and corrosion of either the pin and/or the inside of the carrier. If these pins are dragging, I believe the outside pad would not release completely.
A longer shot ...
When the rear pads are installed, do they drop freely into the carrier?
When the rear pads are installed, can they move freely laterally in the carrier?
If there's corrosion on the carrier and the pads fit too tightly, they might not release even when the caliper pistons retracts after application of the brakes.
The longest (and an unlikely) shot ...
The piston seals get stiff as they age or get overheated. The brakes rely on flexible square cross-section piston seals to distort when braking and then to grap the piston and retract it when the seal "relaxes". You have a relatively new car, and it's difficult to overheat the rear brakes, but I suppose it's possible that a seal is shot, doesn't retract the piston, and the light drag causes the squeal.
<img src="http://www.audipages.com/Tech_Articles/susp_whls_brake_steer/rbrakes1.gif">
2. De-glazed or new pads made the squeal disappear, if only for one day or a few weeks. The squeal returned sooner when the rotors were skimmed, and the pads would bed in sooner in this case also.
I'll guess that at least one of the rear pads is dragging ever so slightly, enough that even just hard cornering gets the pad off the rotor and makes the squeal disappear.
So a few questions:
Are the inside and outside rear pads on both sides wearing evenly?
Are all 4 rubber boots (at #6 in the pic) protecting the sliding pins of the rear caliper carriers intact?
Were these pins re-lubricated with brake caliper grease when the rotors were removed?
Do the pins fit snuggly in the carrier but slide in and out freely?
When the rotors were removed for turning, the caliper carriers also need to be removed. Even if the rubber boots are now installed correctly, one might have been off for a while, allowing water in alongside the pin and corrosion of either the pin and/or the inside of the carrier. If these pins are dragging, I believe the outside pad would not release completely.
A longer shot ...
When the rear pads are installed, do they drop freely into the carrier?
When the rear pads are installed, can they move freely laterally in the carrier?
If there's corrosion on the carrier and the pads fit too tightly, they might not release even when the caliper pistons retracts after application of the brakes.
The longest (and an unlikely) shot ...
The piston seals get stiff as they age or get overheated. The brakes rely on flexible square cross-section piston seals to distort when braking and then to grap the piston and retract it when the seal "relaxes". You have a relatively new car, and it's difficult to overheat the rear brakes, but I suppose it's possible that a seal is shot, doesn't retract the piston, and the light drag causes the squeal.
<img src="http://www.audipages.com/Tech_Articles/susp_whls_brake_steer/rbrakes1.gif">
05-13-2004, 08:35 AM
#3
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thanks randy, some more thoughts
excellent thinking and you've given me some things to work on.
other comments:
1) the rear pads were replaced at the same time as the rotors were skimmed.
2) the operation of the handbrake never makes the squeal worse as it does (noticeably) with the footbrake. the squeal will disappear with a hard application of the handbrake.
3) i assume that the h/brake works the pads physically, while the footbrake works them hydraulically.
all-in-all it makes me think that we have a seal sticking...
other comments:
1) the rear pads were replaced at the same time as the rotors were skimmed.
2) the operation of the handbrake never makes the squeal worse as it does (noticeably) with the footbrake. the squeal will disappear with a hard application of the handbrake.
3) i assume that the h/brake works the pads physically, while the footbrake works them hydraulically.
all-in-all it makes me think that we have a seal sticking...
05-13-2004, 10:53 AM
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Re: "a longer shot" ...
Forgot to mention: I had this problem with my front Alcons.
I went to swap out my Pagid RS4-2-1 street pads before Grattan, but couldn't remove the inner pad on both sides! As you can see from the pic, there's nothing fancy here; the backing plates of the pad is straight-sided, and the pads just drop in and sit on the lip inside the caliper. After struggling with one side for over an hour, I finally gave up, removed the caliper, and twisted the pad out of the caliper.
As it turned out, the pads didn't survive the salty Pennsylvania winter well. The end of the pad's steel backing plate corroded, and the rust jammed the pads in tight against the calipers SS guides. Also, the inner jammed pads were worn less than half the outer pads. The inner pads weren't jammed to tight that they wouldn't budge under the high hydraulic pressure of hard braking, but I suspect they never released completely and were always dragging. Under normal (light) braking, it looks like the outer pads did all the work.
Our rear calipers could have a similar problem, except both the pad's backing plate and the caliper carrier are steel/iron. Since my Stasis rear brakes uses the S4 caliper carrier, I was just playing with my original S8 carriers and a set of new pads. The pad does fit pretty snuggly, and it looks like it wouldn't take much rust to get them stuck in the carrier.
BTW: I now smear a bit of high temp anti-sieze on the sides of the backing plate of my front pads before dropping them into the caliper.
<img src="http://pictureposter.audiworld.com/17157/alconta6_d.jpg">
I went to swap out my Pagid RS4-2-1 street pads before Grattan, but couldn't remove the inner pad on both sides! As you can see from the pic, there's nothing fancy here; the backing plates of the pad is straight-sided, and the pads just drop in and sit on the lip inside the caliper. After struggling with one side for over an hour, I finally gave up, removed the caliper, and twisted the pad out of the caliper.
As it turned out, the pads didn't survive the salty Pennsylvania winter well. The end of the pad's steel backing plate corroded, and the rust jammed the pads in tight against the calipers SS guides. Also, the inner jammed pads were worn less than half the outer pads. The inner pads weren't jammed to tight that they wouldn't budge under the high hydraulic pressure of hard braking, but I suspect they never released completely and were always dragging. Under normal (light) braking, it looks like the outer pads did all the work.
Our rear calipers could have a similar problem, except both the pad's backing plate and the caliper carrier are steel/iron. Since my Stasis rear brakes uses the S4 caliper carrier, I was just playing with my original S8 carriers and a set of new pads. The pad does fit pretty snuggly, and it looks like it wouldn't take much rust to get them stuck in the carrier.
BTW: I now smear a bit of high temp anti-sieze on the sides of the backing plate of my front pads before dropping them into the caliper.
<img src="http://pictureposter.audiworld.com/17157/alconta6_d.jpg">
05-20-2004, 11:29 PM
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another update
got the car in the shop, after working with the dealer lead technican on an approach...
this saw the car up on the lift, the abs pump disabled, and 100km/hr achieved (virtually).
the squeal:
1) was front left brembo
2) remained upon pad replacement
the disc is true, the calliper straight, and no-one has any real idea what is the culprit. the discs at the front are being replaced overnight, and we will see if that has fixed the fault.
i know a bit about cars, but this sort of fault makes me think that the dealer tech earns his money.
on the plus side, with the car out of warranty in 6 months, i now have 2 new front discs, and 4 new brake pads :-)
this saw the car up on the lift, the abs pump disabled, and 100km/hr achieved (virtually).
the squeal:
1) was front left brembo
2) remained upon pad replacement
the disc is true, the calliper straight, and no-one has any real idea what is the culprit. the discs at the front are being replaced overnight, and we will see if that has fixed the fault.
i know a bit about cars, but this sort of fault makes me think that the dealer tech earns his money.
on the plus side, with the car out of warranty in 6 months, i now have 2 new front discs, and 4 new brake pads :-)
09-24-2011, 08:36 PM
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dealing with the same issue here in the tropics. Had new rotors, brake pads, calipers refurbished, new brake lines, still annoying squealing ONLY at low speeds, a bit embarrassing, given the otherwise fine car.
Some here have suggested big red ceramic brake pads. Will try at the next go. But not many options for the D2 S8.
Cheers
Some here have suggested big red ceramic brake pads. Will try at the next go. But not many options for the D2 S8.
Cheers
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09-25-2011, 06:00 AM
#8
AudiWorld Super User
I suggest a simple maneuver that has always worked for me, with every German car I've owned...this "adjustment" actually came (where I learned it) straight out of one of my father's Renault owners manuals, back when disc brakes were a less common item:
Floor the car backwards and lock up the brakes a couple of times for "re-adjustment".
Works for me EVERY time, with every combination of disc and pad I've ever had. No more squeal at any speed for months....sometimes much longer.
Much of the brake squeal in many cars comes from brake pads settling too tight into the pad-to-caliper sliding surfaces...I also buff down and coat those surfaces with high-impact grease when I first install the pads, and often maybe once more during the pads' lives.
More often than not, brake squeal is not a product of materials (maybe more likely with some?), but just normal resonance being transmitted through the caliper, when the pads have settled too well (from being shoved in the same direction constantly) and lost their necessary independent "floating" ability.
Floor the car backwards and lock up the brakes a couple of times for "re-adjustment".
Works for me EVERY time, with every combination of disc and pad I've ever had. No more squeal at any speed for months....sometimes much longer.
Much of the brake squeal in many cars comes from brake pads settling too tight into the pad-to-caliper sliding surfaces...I also buff down and coat those surfaces with high-impact grease when I first install the pads, and often maybe once more during the pads' lives.
More often than not, brake squeal is not a product of materials (maybe more likely with some?), but just normal resonance being transmitted through the caliper, when the pads have settled too well (from being shoved in the same direction constantly) and lost their necessary independent "floating" ability.
09-30-2011, 05:57 AM
#9
AudiWorld Member
Using some pad insulating material (sprayed on) hasn't been mentioned.
Also; if you have any air in your system (this could be caused by old fluid BTW)
results in the pad(s) not retracting (completely) from the rotor.
Do not put lube or DOT 4 brake fluid on the seal ring or piston when it is first assembled into the caliper. I know this sounds off the wall but the seal will roll (slightly), allowing the piston to retract fully, which it will not do if it has been pre-lubed.
pc
Also; if you have any air in your system (this could be caused by old fluid BTW)
results in the pad(s) not retracting (completely) from the rotor.
Do not put lube or DOT 4 brake fluid on the seal ring or piston when it is first assembled into the caliper. I know this sounds off the wall but the seal will roll (slightly), allowing the piston to retract fully, which it will not do if it has been pre-lubed.
pc
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