brake pedal travel
03-16-2004, 07:43 AM
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brake pedal travel
I've read posts that people talk about the brake pedal travle being too long. does anyone have any advice on how to decrease the travel or make the brakes grab quicker.
I just did new rotor, pads, stainless steel lines, and fluid last night and the pedal travel seems to be about the same.
How much travel does your brake pedal have before it starts to grab? either in inches or percentage of total travel.
I just did new rotor, pads, stainless steel lines, and fluid last night and the pedal travel seems to be about the same.
How much travel does your brake pedal have before it starts to grab? either in inches or percentage of total travel.
03-16-2004, 08:01 AM
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Don't know if the A4 has this problem, but ...
I'm sitting in my S8 with the hood up, feeling rather unhappy about 5" of brake pedal travel, and making plans to install the new master cylinder I purchased after Audi claimed my brake upgrades caused this problem. Anyway, I pumped the brake pedal in disgust a few times and noticed that the master cylinder was moving!?
The first pic is what you see when you remove the plastic cover at the rear of the engine compartment. The master cylinder sits directly under the brake fluid reservoir and is tilted slightly up, "aiming" at the strut bar (unique to the S8) connecting the shock towers. A neighbor happened to walk by, and I asked him how much the master cylinder moved forward when I pressed on the brake pedal ... about ½" !! With a brake pedal ratio of ~4.5:1, this means that over 2" of brake pedal travel is wasted just moving the master cylinder.
<img src="http://pictureposter.audiworld.com/17157/strutbar.jpg">
OK, I can fix this. I assumed that the firewall was flexing where the master cylinder and vacuum booster assembly bolted to it. I originally planned to make a small strut connecting a M/C bolt and one of the bolts on the shock tower, but the angle was shallower than I wanted, and an electrical connector and one of the hard brake lines were in the way. The flat end of the M/C, though, was only ~3/4" from the strut bar and very close to the end where it bolts to the shock tower. After ~4 hr with a small block of wood, hacksaw, file, and Dremel tool, I have a nice C-shaped piece of wood that slips snugly over the strut bar with an angled face that's tight up against the rear of the M/C.
On my way to the Audi Club Road America event, I stop in Illinois where a friend of my brother makes aluminum sand casting replicas of old toys. He saw the block of wood, made an aluminum copy in about an hour, and you see the finished installation below.
<img src="http://pictureposter.audiworld.com/17157/TheBlock.jpg">
So how well does this work? ...
Of everything I've done with my brakes, the biggest improvement in pedal feel comes from just switching to Ferodo DS3000 track pads. Since their coefficient of friction is more than 50% higher than stock pads, this alone firms up the pedal nicely. Unfortunately, you can't use them on the street. When cold, they screech louder than a scalded cat and are also very abrasive and eat rotors. "The Block" made more of an improvement in pedal feel than everything else combined ... Alcon monobloc calipers, larger rotors front and rear, and braided SS brake lines front and rear. Amazing!!
The first pic is what you see when you remove the plastic cover at the rear of the engine compartment. The master cylinder sits directly under the brake fluid reservoir and is tilted slightly up, "aiming" at the strut bar (unique to the S8) connecting the shock towers. A neighbor happened to walk by, and I asked him how much the master cylinder moved forward when I pressed on the brake pedal ... about ½" !! With a brake pedal ratio of ~4.5:1, this means that over 2" of brake pedal travel is wasted just moving the master cylinder.
<img src="http://pictureposter.audiworld.com/17157/strutbar.jpg">
OK, I can fix this. I assumed that the firewall was flexing where the master cylinder and vacuum booster assembly bolted to it. I originally planned to make a small strut connecting a M/C bolt and one of the bolts on the shock tower, but the angle was shallower than I wanted, and an electrical connector and one of the hard brake lines were in the way. The flat end of the M/C, though, was only ~3/4" from the strut bar and very close to the end where it bolts to the shock tower. After ~4 hr with a small block of wood, hacksaw, file, and Dremel tool, I have a nice C-shaped piece of wood that slips snugly over the strut bar with an angled face that's tight up against the rear of the M/C.
On my way to the Audi Club Road America event, I stop in Illinois where a friend of my brother makes aluminum sand casting replicas of old toys. He saw the block of wood, made an aluminum copy in about an hour, and you see the finished installation below.
<img src="http://pictureposter.audiworld.com/17157/TheBlock.jpg">
So how well does this work? ...
Of everything I've done with my brakes, the biggest improvement in pedal feel comes from just switching to Ferodo DS3000 track pads. Since their coefficient of friction is more than 50% higher than stock pads, this alone firms up the pedal nicely. Unfortunately, you can't use them on the street. When cold, they screech louder than a scalded cat and are also very abrasive and eat rotors. "The Block" made more of an improvement in pedal feel than everything else combined ... Alcon monobloc calipers, larger rotors front and rear, and braided SS brake lines front and rear. Amazing!!
03-16-2004, 08:19 AM
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It's a common problem with many cars, ...
My Saab 900 had a similar problem; and I talked to mechanic for a Porsche race team who said they need to brace the firewall to prevent master cylinder movement.
And it's easy to check -- Pump up the brake pedal, push hard, and have someone under the hood watch what happens.
And it's easy to check -- Pump up the brake pedal, push hard, and have someone under the hood watch what happens.
03-16-2004, 08:45 AM
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how much pressure do you need to apply before your MC would move?
was that half inch using as much force as you would use at the track or just a regular stop on the street? I'm wondering how big of a problem this is for those of us that don't slam our brake pedal through the floorboard.
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03-16-2004, 10:35 AM
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1/2" with a max-effort threshold braking stop, ...
as either on track or during an emergency panic stop on the street, but the master cylinder begins moving with even moderate brake pedal effort.
The improvement in pedal feel, though, is <b>very</b> noticable with even normal street stops. I believe this is one reason why the Ferodo DS3000 track pads do feel so good on the street. Because the cf of these pads is very high, less pedal effort is needed for normal braking, and the M/C moves less. I got similar results from larger front and rear rotor diameters, but not as dramatic.
I had been chasing this soft brake pedal for more than two years and had tried almost everything to remove compliance from the system ... -AN ss brake lines of course, but also replacing the 2-piece Brembo calipers with the extremely rigid Alcon TA-6, MMC (aluminum/ceramic metal matrix) monobloc calipers. [Trust me on this, you don't want to know what they cost.] I was starting to prepare mentally to replace the rear sliding calipers with the Alcon TA-4 or MB-4 MMC calipers when I discovered that by far the majority of the compliance in the brake system is simply movement of the master cylinder.
The bottom line result: My brakes now inspire great confidence, whether street or track.
The improvement in pedal feel, though, is <b>very</b> noticable with even normal street stops. I believe this is one reason why the Ferodo DS3000 track pads do feel so good on the street. Because the cf of these pads is very high, less pedal effort is needed for normal braking, and the M/C moves less. I got similar results from larger front and rear rotor diameters, but not as dramatic.
I had been chasing this soft brake pedal for more than two years and had tried almost everything to remove compliance from the system ... -AN ss brake lines of course, but also replacing the 2-piece Brembo calipers with the extremely rigid Alcon TA-6, MMC (aluminum/ceramic metal matrix) monobloc calipers. [Trust me on this, you don't want to know what they cost.] I was starting to prepare mentally to replace the rear sliding calipers with the Alcon TA-4 or MB-4 MMC calipers when I discovered that by far the majority of the compliance in the brake system is simply movement of the master cylinder.
The bottom line result: My brakes now inspire great confidence, whether street or track.
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