Deterioration of brake pedal "feel"
03-05-2009, 11:59 PM
#1
Race Director
Thread Starter
Deterioration of brake pedal "feel"
I was thinking that even as the pads wear down and the rotors wear down, that as long as I was bleeding and using good fluid, that I'd still have a firm, short pedal.
It doesn't seem that way.
New pads & rotors seem to bring it back though.
Brake lines are good & no caliper spread. Pads bedded in, all that stuff good.
Brakes stop ok, it's just pedal feel seems less than short & firm as the pads & rotors wear.
Should this be? If so, why?
No guesses please.
It doesn't seem that way.
New pads & rotors seem to bring it back though.
Brake lines are good & no caliper spread. Pads bedded in, all that stuff good.
Brakes stop ok, it's just pedal feel seems less than short & firm as the pads & rotors wear.
Should this be? If so, why?
No guesses please.
03-06-2009, 12:51 AM
#2
Former Vendor
I was thinking that even as the pads wear down and the rotors wear down, that as long as I was bleeding and using good fluid, that I'd still have a firm, short pedal.
It doesn't seem that way.
New pads & rotors seem to bring it back though.
Brake lines are good & no caliper spread. Pads bedded in, all that stuff good.
Brakes stop ok, it's just pedal feel seems less than short & firm as the pads & rotors wear.
Should this be? If so, why?
No guesses please.
It doesn't seem that way.
New pads & rotors seem to bring it back though.
Brake lines are good & no caliper spread. Pads bedded in, all that stuff good.
Brakes stop ok, it's just pedal feel seems less than short & firm as the pads & rotors wear.
Should this be? If so, why?
No guesses please.
Easy, as the pistons move further out, the volume of the system increases. The master has a set amount of fluid it moves. So as the volume increases the amount of brake pedal travel increases.
Randy
03-06-2009, 01:19 AM
#3
Burning Brakes
Not unless when you release the pedal the pistons pull back farther from the pads/rotors as they wear. Do they? A given amount of pedal travel will move the pistons the exact same amount no matter where the pistons are in the bore.
03-06-2009, 01:28 AM
#4
Former Vendor
Randy
03-06-2009, 04:10 AM
#6
Racer
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I noticed this the other day with the stoptech ST40 calipers. Dumped my
half-used HPS pads, installed Axxis Ultimates and woop, the pedal was
higher and firmer. A lot. I assumed that it was the different pad types, not
with any particular justification.
I know I'm not allowed to guess, but...
One reason might be that the piston seals are not as rigid when the piston
is extended further (sounds improbable).
Another reason might be that the piston and the pad are no longer
perpendicular (ie: caliper spreading). So each time pressure is applied, a little
bit of the fluid volume is used to rotate the piston about its axis so that it fully
mates with the rear of the pad.
<runs out and measures the HPS's>
Yup, 0.2mm difference. So if my theory is correct then when the brakes are
released, one side of the piston is touching the pad while the other side of
the piston has about a 0.1mm gap. So it will require about 0.05mm piston
travel before the piston is fully mated against the rear of the pad. Dunno if
that's a noticeable amount of travel though.
Of course, it could be that the piston does not straighten itself up when it
is released from a wedge-shaped pad, in which case my theory is bunk.
But you did ask for guesses, didn't you?
half-used HPS pads, installed Axxis Ultimates and woop, the pedal was
higher and firmer. A lot. I assumed that it was the different pad types, not
with any particular justification.
I know I'm not allowed to guess, but...
One reason might be that the piston seals are not as rigid when the piston
is extended further (sounds improbable).
Another reason might be that the piston and the pad are no longer
perpendicular (ie: caliper spreading). So each time pressure is applied, a little
bit of the fluid volume is used to rotate the piston about its axis so that it fully
mates with the rear of the pad.
<runs out and measures the HPS's>
Yup, 0.2mm difference. So if my theory is correct then when the brakes are
released, one side of the piston is touching the pad while the other side of
the piston has about a 0.1mm gap. So it will require about 0.05mm piston
travel before the piston is fully mated against the rear of the pad. Dunno if
that's a noticeable amount of travel though.
Of course, it could be that the piston does not straighten itself up when it
is released from a wedge-shaped pad, in which case my theory is bunk.
But you did ask for guesses, didn't you?
03-06-2009, 12:02 PM
#7
Safety Car
Isn't this why the frugal types often stuff a old backing plate as a spacer between the pistons and the pad? I know some folks say "heat barrier" but ... ;-)
03-06-2009, 12:43 PM
#8
Drifting
Piston knock back........thats why you have to pump the pedal in a 'holy crap' manner on occasion......it WILL increase the 'sphincter factor' if you aren't expecting it. Not so much on a solo pad.........
03-06-2009, 02:44 PM
#9
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Pad taper.
As they wear, pads lose their "parallelism" (just invented that word...pretty good, huh ?). Leading end of the pad wears differently than the trailing edge, due to temperature, "firebrand wipe", etc. etc. etc.
As they get "unparallel", you'll get more piston movement required to go from "relaxed" to "CLAMP THAT SUCKER".
Easy way to check is just take the pads out, and stack them face to face. If you can see any difference in wear between the leading and trailing ends, THAT is your problem. If you've got really big pads and multiple pistons, you can feel the problem without it even being visually apparent. I have Wilwood 6-piston GN calipers on one of the race fleet, and the big-*** pads & caliper layout are really susceptible to longer pedal travel as the pads get tapered.
As they wear, pads lose their "parallelism" (just invented that word...pretty good, huh ?). Leading end of the pad wears differently than the trailing edge, due to temperature, "firebrand wipe", etc. etc. etc.
As they get "unparallel", you'll get more piston movement required to go from "relaxed" to "CLAMP THAT SUCKER".
Easy way to check is just take the pads out, and stack them face to face. If you can see any difference in wear between the leading and trailing ends, THAT is your problem. If you've got really big pads and multiple pistons, you can feel the problem without it even being visually apparent. I have Wilwood 6-piston GN calipers on one of the race fleet, and the big-*** pads & caliper layout are really susceptible to longer pedal travel as the pads get tapered.
03-06-2009, 03:04 PM
#11
Race Director
Thread Starter
Pad taper.
As they wear, pads lose their "parallelism" (just invented that word...pretty good, huh ?). Leading end of the pad wears differently than the trailing edge, due to temperature, "firebrand wipe", etc. etc. etc.
As they get "unparallel", you'll get more piston movement required to go from "relaxed" to "CLAMP THAT SUCKER".
Easy way to check is just take the pads out, and stack them face to face. If you can see any difference in wear between the leading and trailing ends, THAT is your problem. If you've got really big pads and multiple pistons, you can feel the problem without it even being visually apparent. I have Wilwood 6-piston GN calipers on one of the race fleet, and the big-*** pads & caliper layout are really susceptible to longer pedal travel as the pads get tapered.
As they wear, pads lose their "parallelism" (just invented that word...pretty good, huh ?). Leading end of the pad wears differently than the trailing edge, due to temperature, "firebrand wipe", etc. etc. etc.
As they get "unparallel", you'll get more piston movement required to go from "relaxed" to "CLAMP THAT SUCKER".
Easy way to check is just take the pads out, and stack them face to face. If you can see any difference in wear between the leading and trailing ends, THAT is your problem. If you've got really big pads and multiple pistons, you can feel the problem without it even being visually apparent. I have Wilwood 6-piston GN calipers on one of the race fleet, and the big-*** pads & caliper layout are really susceptible to longer pedal travel as the pads get tapered.
03-06-2009, 03:05 PM
#12
Melting Slicks
As long as you have a good bleed and not boiled over brake fluid. It was my understand that pad taper with stock C5 calipers and race pads. The more they taper the deeper that pedal feel gets. The car still stops but it isn't a good feeling. Fresh set of pads and voila, good pedal feel.
To help control tapering I have been swapping the pads in the front left to right after day 1 at a 2 day DE. Helps with that pedal feel and gets me maybe an extra weekend out of the pads.
The only race pads I have used on track so far are Carbotechs. They are kinda soft and taper fast in the stock caliper.
To help control tapering I have been swapping the pads in the front left to right after day 1 at a 2 day DE. Helps with that pedal feel and gets me maybe an extra weekend out of the pads.
The only race pads I have used on track so far are Carbotechs. They are kinda soft and taper fast in the stock caliper.
03-06-2009, 03:10 PM
#13
Race Director
Thread Starter
As long as you have a good bleed and not boiled over brake fluid. It was my understand that pad taper with stock C5 calipers and race pads. The more they taper the deeper that pedal feel gets. The car still stops but it isn't a good feeling. Fresh set of pads and voila, good pedal feel.
To help control tapering I have been swapping the pads in the front left to right after day 1 at a 2 day DE. Helps with that pedal feel and gets me maybe an extra weekend out of the pads.
The only race pads I have used on track so far are Carbotechs. They are kinda soft and taper fast in the stock caliper.
To help control tapering I have been swapping the pads in the front left to right after day 1 at a 2 day DE. Helps with that pedal feel and gets me maybe an extra weekend out of the pads.
The only race pads I have used on track so far are Carbotechs. They are kinda soft and taper fast in the stock caliper.
So when you swap tapered pads do you put the taper end up or down?
03-06-2009, 04:12 PM
#14
Melting Slicks
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As long as you have a good bleed and not boiled over brake fluid. It was my understand that pad taper with stock C5 calipers and race pads. The more they taper the deeper that pedal feel gets. The car still stops but it isn't a good feeling. Fresh set of pads and voila, good pedal feel.
To help control tapering I have been swapping the pads in the front left to right after day 1 at a 2 day DE. Helps with that pedal feel and gets me maybe an extra weekend out of the pads.
The only race pads I have used on track so far are Carbotechs. They are kinda soft and taper fast in the stock caliper.
To help control tapering I have been swapping the pads in the front left to right after day 1 at a 2 day DE. Helps with that pedal feel and gets me maybe an extra weekend out of the pads.
The only race pads I have used on track so far are Carbotechs. They are kinda soft and taper fast in the stock caliper.
Frank Gonzalez
03-06-2009, 04:15 PM
#15
Melting Slicks
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Change the pad to the opposite side of the rotor and you will extend its life by minimizing tapering.
Frank Gonzalez
03-06-2009, 04:17 PM
#16
Melting Slicks
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Pad taper.
As they wear, pads lose their "parallelism" (just invented that word...pretty good, huh ?). Leading end of the pad wears differently than the trailing edge, due to temperature, "firebrand wipe", etc. etc. etc.
As they get "unparallel", you'll get more piston movement required to go from "relaxed" to "CLAMP THAT SUCKER".
Easy way to check is just take the pads out, and stack them face to face. If you can see any difference in wear between the leading and trailing ends, THAT is your problem. If you've got really big pads and multiple pistons, you can feel the problem without it even being visually apparent. I have Wilwood 6-piston GN calipers on one of the race fleet, and the big-*** pads & caliper layout are really susceptible to longer pedal travel as the pads get tapered.
As they wear, pads lose their "parallelism" (just invented that word...pretty good, huh ?). Leading end of the pad wears differently than the trailing edge, due to temperature, "firebrand wipe", etc. etc. etc.
As they get "unparallel", you'll get more piston movement required to go from "relaxed" to "CLAMP THAT SUCKER".
Easy way to check is just take the pads out, and stack them face to face. If you can see any difference in wear between the leading and trailing ends, THAT is your problem. If you've got really big pads and multiple pistons, you can feel the problem without it even being visually apparent. I have Wilwood 6-piston GN calipers on one of the race fleet, and the big-*** pads & caliper layout are really susceptible to longer pedal travel as the pads get tapered.
Frank Gonzalez
03-06-2009, 04:49 PM
#17
Melting Slicks
I got some lightly used Hawk DTC70s from Joe that I am going to try in a couple of weeks. If I understand it right the Hawks will wear slower but the rotors will wear/crack faster. NAPA blanks are cheaper than new pads so it seems like a fair trade. Even if swapping rotors is more time consuming.
03-06-2009, 05:37 PM
#18
Race Director
Thread Starter
It is not a question of top or bottom. The leading edge of the pad wears more than the trailing edge. In the front brakes the leading edge is at the bottom. In the rear brakes the leading edge is at the top.
Change the pad to the opposite side of the rotor and you will extend its life by minimizing tapering.
Frank Gonzalez
Change the pad to the opposite side of the rotor and you will extend its life by minimizing tapering.
Frank Gonzalez
03-06-2009, 05:41 PM
#19
Former Vendor
We found a trick a long time ago for pad taper. Put a 45 degree angle on the leading edge of the pad. No more "end milling" so to speak. You can run this 45 degree about 1/2 inch down the pad.
Randy
Randy
03-06-2009, 07:34 PM
#20
Melting Slicks
As you describe the leading edge of the pad always wears more than the trailing edge, which is a normal wear pattern.