Braking problem and pad suggestions
12-25-2010, 05:36 PM
#1
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Braking problem and pad suggestions
My car is a '91 miata and the brake system is 100% stock, the car has 207,000 miles on it. I've noticed around the same time that I addes forced induction to the car the brakes have been going.
Now I have to pump the brakes to build up pressure so i can stop the car it seems. but most of the time it stops normally with the brakes engaging with the pedal nice and high where it should be. Other times I have to pump the brake pedal at least once to build up pressure because the first time the pedal just goes straight to the floor and does nothing to stop the car until I pump again!!!!
I've been told that maybe boost is getting into my brake booster but it does this even if I haven't gotten into boost yet sometimes, and sometimes I will have gone into boost but the brakes are fine. Nothing is consistant. Maybe there's air in the lines somehow or maybe my booster is going out? I have no idea.
After I fix the big brake problem I need to replace these old pads. I do a lot of canyon driving, daily driving, and a few roadcourse and auto-x events here and there. What would be a good pad for that? I was looking at Hawk HPS and maybe some SS lines.
Now I have to pump the brakes to build up pressure so i can stop the car it seems. but most of the time it stops normally with the brakes engaging with the pedal nice and high where it should be. Other times I have to pump the brake pedal at least once to build up pressure because the first time the pedal just goes straight to the floor and does nothing to stop the car until I pump again!!!!
I've been told that maybe boost is getting into my brake booster but it does this even if I haven't gotten into boost yet sometimes, and sometimes I will have gone into boost but the brakes are fine. Nothing is consistant. Maybe there's air in the lines somehow or maybe my booster is going out? I have no idea.
After I fix the big brake problem I need to replace these old pads. I do a lot of canyon driving, daily driving, and a few roadcourse and auto-x events here and there. What would be a good pad for that? I was looking at Hawk HPS and maybe some SS lines.
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12-25-2010, 07:39 PM
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Diagnose this in steps:
1. bleed the system
2. check the 1-way valve in the booster (these rarely fail): go into boost, stomp the brake and hold, then let off the gas
3. check for knock back (see below)
I bet you have pad knock back. Crank the wheel left and right hard, then stomp on the brakes...does the pedal drop then get hard after you check-up on the pedal? Now slightly pull the e-brake and crank the wheel back and for and check for play in the pedal. Finally ride the brake pedal, crank the wheel left and right, then check for play. It's easier to diagnose front to rear, left and right knock back problems with this method than checking for radial play in the bearings/hubs. The dial indicator can lie due to the position of the pads and the amount of load on the bearings to induce play. I spent half a season and $1500 chasing knock-back problems; learn from my mcstakes.
A long pedal on cold brakes does not indicate a pad compound problem. Usually a bad check-valve in the booster translates to extreme pedal pressure needed to stop the car (no vacuum "lever advantage").
1. bleed the system
2. check the 1-way valve in the booster (these rarely fail): go into boost, stomp the brake and hold, then let off the gas
3. check for knock back (see below)
I bet you have pad knock back. Crank the wheel left and right hard, then stomp on the brakes...does the pedal drop then get hard after you check-up on the pedal? Now slightly pull the e-brake and crank the wheel back and for and check for play in the pedal. Finally ride the brake pedal, crank the wheel left and right, then check for play. It's easier to diagnose front to rear, left and right knock back problems with this method than checking for radial play in the bearings/hubs. The dial indicator can lie due to the position of the pads and the amount of load on the bearings to induce play. I spent half a season and $1500 chasing knock-back problems; learn from my mcstakes.
A long pedal on cold brakes does not indicate a pad compound problem. Usually a bad check-valve in the booster translates to extreme pedal pressure needed to stop the car (no vacuum "lever advantage").
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12-25-2010, 08:23 PM
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Regarding what pads to use, I had HPS for a while. For canyon carving they were pretty decent, but as soon as I got on track, they were ****. I'm on HP+, and they do ok on track, but I'm going with something better next time.
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12-25-2010, 08:44 PM
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Racetracks require a track-pad, period. I don't know why you guys waste your time on street pads when you can use something with more bite and even torque-temp. I got to the point where I was cooking HP+in 90-minutes of track time on Azenis with 86whp. I then switched to Hawk blue and I never knew what I was missing.
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12-25-2010, 09:31 PM
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I will follow your procedure tomorrow night if I have time. It might have to wait until monday. I will be out of town until then. I hope it's just air in the line. Kinda odd though. I don't see how air could get in. They have been fine for a long time.
I only do a track day once or twice per year so maybe the Hawk HPS pads will do fine for me. How are the blue for daily driving? I bet they eat rotors in a week.
I only do a track day once or twice per year so maybe the Hawk HPS pads will do fine for me. How are the blue for daily driving? I bet they eat rotors in a week.
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12-25-2010, 09:40 PM
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How does brake knock back make the pedal go to the floor like that?
NVM, I googled it. I'm almost certain it's pad knockback now. I remember it was much worse in the canyon than it was driving to work and that's almost all straight.
NVM, I googled it. I'm almost certain it's pad knockback now. I remember it was much worse in the canyon than it was driving to work and that's almost all straight.
Last edited by Cookie Monster; 12-25-2010 at 09:58 PM.
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12-27-2010, 06:29 PM
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In for info on DD'ing blues.
EDIT: A search revealed that Hawk Blues will eat through rotors. I guess...in for info on DDing something like a DTC 30.
Last edited by MartinezA92; 12-27-2010 at 10:54 PM.
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01-03-2011, 09:09 PM
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It turns out that the right fron caliper had a slight leak in it. I rebuilt the front calipers with news seals and now the pedal feels firm but I have a new problem.....
The drivers front caliper doesn't have enough pressure to work properly! It Sorta works but I can rotate it with a breaker bar while the pedal is being pressed! When I replaced the line with the SS line and put it all back together the fluid from the resivoir was all let out. I've been told the brake proportioning valve has now blocked that line off from getting the presure it needs because it's a safety feature. How do I reset it?
The drivers front caliper doesn't have enough pressure to work properly! It Sorta works but I can rotate it with a breaker bar while the pedal is being pressed! When I replaced the line with the SS line and put it all back together the fluid from the resivoir was all let out. I've been told the brake proportioning valve has now blocked that line off from getting the presure it needs because it's a safety feature. How do I reset it?
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01-03-2011, 09:59 PM
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01-03-2011, 10:21 PM
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Daily driving a track pad will destroy your rotors. Any Hawk pads can be swapped on the same rotor without rebedding. I was running HP+ for autocross and HT-10 for track all this year without issue.
When I replaced the line with the SS line and put it all back together the fluid from the resivoir was all let out. I've been told the brake proportioning valve has now blocked that line off from getting the presure it needs because it's a safety feature. How do I reset it?
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01-05-2011, 02:59 AM
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Besides, stock Miata rotors are like $15 each, aren't they?
--Ian
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