1999 - A8 braking problems
11-03-2002, 02:01 AM
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1999 - A8 braking problems
I have a 1999 A8 4.2Q and i've changed the braking discs 5 times. Finaly i put Brembo Braking system on the car but after 3000 km i have again a big trepidation at 120km/h. Does anybody had such a problem? I don't know what to do anymore.
11-03-2002, 02:53 AM
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Can you provide some additional information?
.
Exactly what were the symptoms of the problem that resulted in the 5 disc replacements? Have you always used Audi original equipment brake pads?
When you say "trepidation at 120 km/h", do you mean vibration? If so, do you have vibration when braking from 120 km/hr, or vibration at 120 km/hr without braking? Except for this, is everything else normal?
Is the Brembo system you installed identical to the S8's 4-pot brake calipers? Are you also using the S8 rotor? What brake pads are you using?
Do you take the car to the track or did this problem develop only from street use?
Exactly what were the symptoms of the problem that resulted in the 5 disc replacements? Have you always used Audi original equipment brake pads?
When you say "trepidation at 120 km/h", do you mean vibration? If so, do you have vibration when braking from 120 km/hr, or vibration at 120 km/hr without braking? Except for this, is everything else normal?
Is the Brembo system you installed identical to the S8's 4-pot brake calipers? Are you also using the S8 rotor? What brake pads are you using?
Do you take the car to the track or did this problem develop only from street use?
11-03-2002, 04:49 AM
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A8 braking problems
I allways used Audi original parts.The vibration appear when i push the braking pedal.It is a very strong vibration.The brake pads i use now are provided by Brembo.The discs are ventilated and the calipers are with 4 pistons.
I get the car to the Audi service and they told me that the discs are ok. Also they didn't find anything else. I don't know what to do.
I get the car to the Audi service and they told me that the discs are ok. Also they didn't find anything else. I don't know what to do.
11-03-2002, 08:31 AM
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Possible causes of pedal vibration during braking (long) ...
.
Some thoughts/ideas,
1. ABS activates under normal braking -- If you don't see the ABS warning light, I doubt that this is the problem.
2. Warped rotor, excessive run-out -- Since your Audi dealer has checked this, it's probably not the problem.
3. Swapping to a dissimilar pad -- The pads are designed to leave a VERY thin deposit on the rotor. If you change to a different pad, at some point the rotor will have deposits from both. If the coefficient of friction between the new pad is different with the two different pad deposits, you'll experience vibration until the old deposit is worn away (I've had this problem). Or worse yet, the different pad deposit can result in severe galling of the rotor, which I've also seen (but thankfully not on my car). Since you used only Audi pads with the first 5 rotors, or a Brembo pad with your current set-up, this is not the problem.
4. Using a race only pad on the street -- Especially if the pad has not been properly bedded, you may have an uneven pad deposit on the rotor, which causes vibration as in #3 above. Can you determine exactly what pad compound your currently using, or confirm that it's a street pad?
5. Cracked rotor -- Especially if you now have drilled rotors not made by Brembo, cracks can initiate at the holes, grow radially from hole to hole, and cause vibration especially when the rotor is very hot. The crack will tend to close when the rotor is cold, and the crack can occur on either side of the rotor. As a result, your rotors need to be removed from the car, and both sides must be carefully examined.
I lost the link I had to a great photo of a crack across a drilled rotor, it looked like the holes were connected with stitching, but this photo shows what can happen. Needless to say, these rotors are close to a catastrophic failure, a major safety issue.
<img src="http://www.mouthbreather.net/images/rotors_small.jpg">
Surface cracks, like those in the photo of the rotor on my S8, are not a problem.
<img src="http://pictureposter.audiworld.com/17157/rotorcracks.jpg">
6. Rotor distorts under pressure -- I've never seen this, but others have reported this can occur if the wheel bolts are not properly torqued in the proper order when the wheel is mounted. I gather that you're not located in the U.S.; but here, half of the mechanics I've seen either don't properly torque wheels or don't know how. If I didn't personally witness a mechanic torque my wheels, I'll redo it myself when I get home.
6. Bad wheel bearing -- This can cause vibration under braking loads. Since you've had a vibration problem with 6 rotors now, perhaps this is the problem?
7. An A6 owner reported that his problem with vibration under braking was caused by worn tie rods.
Well ... this is about all I can think of. Good luck!
Some thoughts/ideas,
1. ABS activates under normal braking -- If you don't see the ABS warning light, I doubt that this is the problem.
2. Warped rotor, excessive run-out -- Since your Audi dealer has checked this, it's probably not the problem.
3. Swapping to a dissimilar pad -- The pads are designed to leave a VERY thin deposit on the rotor. If you change to a different pad, at some point the rotor will have deposits from both. If the coefficient of friction between the new pad is different with the two different pad deposits, you'll experience vibration until the old deposit is worn away (I've had this problem). Or worse yet, the different pad deposit can result in severe galling of the rotor, which I've also seen (but thankfully not on my car). Since you used only Audi pads with the first 5 rotors, or a Brembo pad with your current set-up, this is not the problem.
4. Using a race only pad on the street -- Especially if the pad has not been properly bedded, you may have an uneven pad deposit on the rotor, which causes vibration as in #3 above. Can you determine exactly what pad compound your currently using, or confirm that it's a street pad?
5. Cracked rotor -- Especially if you now have drilled rotors not made by Brembo, cracks can initiate at the holes, grow radially from hole to hole, and cause vibration especially when the rotor is very hot. The crack will tend to close when the rotor is cold, and the crack can occur on either side of the rotor. As a result, your rotors need to be removed from the car, and both sides must be carefully examined.
I lost the link I had to a great photo of a crack across a drilled rotor, it looked like the holes were connected with stitching, but this photo shows what can happen. Needless to say, these rotors are close to a catastrophic failure, a major safety issue.
<img src="http://www.mouthbreather.net/images/rotors_small.jpg">
Surface cracks, like those in the photo of the rotor on my S8, are not a problem.
<img src="http://pictureposter.audiworld.com/17157/rotorcracks.jpg">
6. Rotor distorts under pressure -- I've never seen this, but others have reported this can occur if the wheel bolts are not properly torqued in the proper order when the wheel is mounted. I gather that you're not located in the U.S.; but here, half of the mechanics I've seen either don't properly torque wheels or don't know how. If I didn't personally witness a mechanic torque my wheels, I'll redo it myself when I get home.
6. Bad wheel bearing -- This can cause vibration under braking loads. Since you've had a vibration problem with 6 rotors now, perhaps this is the problem?
7. An A6 owner reported that his problem with vibration under braking was caused by worn tie rods.
Well ... this is about all I can think of. Good luck!
11-03-2002, 06:12 PM
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are all the parts where they should be?
It may sound like a stupid question but I had a ford a few years ago and in three months I had four or five complete brake systems installed. Only to find that it still did not fix the problem. Then one day I decided to look under the truck for myself (this is impressive since I know very little about cars). What I saw amazed me. A bushing was missing and none of the idiots at the dealership noticed this. $15 in bushings latter and the problem was fixed. So I ask, are all the parts that are supposed to be there, really there.
Just my very uniformed 2 cents
Brent
Just my very uniformed 2 cents
Brent
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