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Old 05-06-2016, 02:00 PM   #1
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Default Bad Pedal Feel, possibly parking brake related?

So I swapped out for new pads (DTC-60's) and my pedal feel has gone to ****. Stock ABS brakes ('99), and the pedal is spongy for the first 1-2" of travel and then rock solid. Pedal spongyness does not get better if the brakes are pumped, and once the rock solid point is reached the car stops fantastically. Spongy travel does not change at all, under track conditions or regular road driving. I had this problem initially when I bought the car, and finally had it fixed last year with the set of HP+ I had. I bled the brakes (including cycling the ABS with the TBS + Ground jumpered in the diag box) using the 2 person method and have no air left within the system.

I can't remember what fixed it the last time, but I think I wound up setting the rear parking brake adjusters tighter than most seem to recommend (tight then back off 1/3rd turn). I did adjust both the slack at the pedal as well as the parking brake, combined with endless amounts of bleeding. How concerned should I be about a bit of drag on the rear pads? I think what I'm feeling is the rear brakes being too loose on the adjustment, resulting in excessive travel of the caliper. I'm going to try only backing them off a 1/4 turn and see if that makes a difference, I'm just concerned with the drag on the pads.
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Old 05-06-2016, 02:13 PM   #2
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You may find that winding them in to tight is now more than a one third turn. New pads should be seated and then the parking brake re-set.

I normally only do a 1/4 turn on the readjusting and have never hit a problem.
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Old 05-06-2016, 02:57 PM   #3
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Makes sense, will adjust and report back. When you say the pads should be seated, is this as simple as pressing the brake pedal or should it involve bedding the pads? I bled the brakes then adjusted the ebrake, wondering if that's enough or if I should always do the ebrake again after bedding pads.
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Old 05-06-2016, 03:16 PM   #4
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The piston should self adjust. The parking brake adjustment is for adjusting the parking brake.

Even if you don't adjust the parking brake at all, you should be able to pump the brakes and bring the piston out to where it should be. The hand brake will feel like garbage and may not hold, but the pedal should feel fine. I don't suggest doing it this way, just making a point. I think something else is going on.
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Old 05-06-2016, 04:42 PM   #5
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Quote:
Originally Posted by TrueChaos View Post
Makes sense, will adjust and report back. When you say the pads should be seated, is this as simple as pressing the brake pedal or should it involve bedding the pads? I bled the brakes then adjusted the ebrake, wondering if that's enough or if I should always do the ebrake again after bedding pads.
I readjust after bedding. And as Williams805 says, there could be something else going on there.
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Old 05-06-2016, 06:31 PM   #6
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How are your rotors? I've fixed spongy brakes on two cars (one on a miata, after adjusting everything, bleeding well, replacing master and replacing hoses) by replacing excessively worn rotors. Sounds retarded I know. I assume it's excessive pad travel to hit the worn rotor, although I'm Well Aware of how hydraulic brakes self adjust.
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Old 05-06-2016, 07:09 PM   #7
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How are your rotors? I've fixed spongy brakes on two cars (one on a miata, after adjusting everything, bleeding well, replacing master and replacing hoses) by replacing excessively worn rotors. Sounds retarded I know. I assume it's excessive pad travel to hit the worn rotor, although I'm Well Aware of how hydraulic brakes self adjust.
Rotors are brand new.

Trip report: One caliper needed a full 3 turns to tight, backed off 1/4 turn and re-set. I could spin the wheel with the parking brake engaged before the readjustment. The first stop felt great, after that it returned to mushyness. Jacked it back up, set the parking brake, and I can spin the one wheel again... not easily, but it's possible, and if I can do it by hand it's clearly backing off of the adjusted point. Regardless of feel, it'll still lock the wheels at 80mph on mostly dead 225 rs3's.

Looks like I'm in for my 3rd rebuilt caliper on that side. Replaced both rears due to age, the next time I did brakes I had fluid in the adjuster area so time for another rebuilt caliper, and now this. I will say the adjuster on that side seemed to bind frequently when adjusting, so I guess I shouldn't be too surprised. I was checking temps coming off the track with an IR thermometer and both rears were pretty even. I've got a track day on monday though, time to see if I can get a caliper tomorrow.
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Old 05-06-2016, 07:17 PM   #8
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You've buggered the end of the adjuster. They're soft (brass?) so they won't bugger up the gear. Not sure if you can replace the adjuster without getting a new caliper.

Edit: Yes, you can. P/N BW0H26733. About 8 bucks a pop.
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Old 05-06-2016, 07:20 PM   #9
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How's your rotor runout? Are you getting pad kickback?
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Old 05-06-2016, 07:50 PM   #10
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Originally Posted by rleete View Post
You've buggered the end of the adjuster. They're soft (brass?) so they won't bugger up the gear. Not sure if you can replace the adjuster without getting a new caliper.

Edit: Yes, you can. P/N BW0H26733. About 8 bucks a pop.
The end of the adjuster is fine, I pulled it to double check when I realized I had to re-tighten the caliper. The problem is that it seems to bind after around a turn or so, at which point I need to put a bit of weight behind it to get it past whatever is causing the bind. Once it's past whatever is binding it, It'll spin freely for another half to full turn, rinse and repeat. I had the adjustment set properly (tight to the point where you can't spin the wheel, then back off a 1/4-1/3rd of a turn. With this method I can spin the wheel with a minor amount of drag with the parking brake off, and can't spin it at all with the parking brake engaged. After going out and doing a few hard stops, waiting for the brakes to cool, jacking the car and setting the ebrake I can turn the wheel by hand again.

Hornetball - Rotors were new when I installed the pads, and have a single trackday on them now. I don't have a runout gauge - if runout was the issue wouldn't I be getting a decent amount of vibration? I'm not noticing and shaking / vibration under hard braking. As for pad kickback - wouldn't that be solved by pumping the brakes? A few pumps doesn't change the pedal height - and I'm getting some braking force from the spongy start of the pedal.

I get the impression that the screw driving the piston forward (and responsible for holding it forward) has worn, and when things heat up the piston can 'skip' over the threads. See:


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Old 05-06-2016, 09:22 PM   #11
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Is there a special procedure for bleeding ABS cars?
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Old 05-06-2016, 09:35 PM   #12
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Quote:
Originally Posted by TrueChaos View Post
The problem is that it seems to bind after around a turn or so, at which point I need to put a bit of weight behind it to get it past whatever is causing the bind. Once it's past whatever is binding it, It'll spin freely for another half to full turn, rinse and repeat.

I get the impression that the screw driving the piston forward (and responsible for holding it forward) has worn, and when things heat up the piston can 'skip' over the threads.
Sounds to me like the threads in the piston are hosed. Since the screw looks okay, I'd assume the other mating thread is the culprit. Stripped out, worn out or just plain the wrong size. Hence the bind/unbind as the screw turns in the piston.
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Old 05-08-2016, 02:34 PM   #13
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I fought with the adjusters until I ditched em. I would adjust em and pedal would be high and solid. Slowly through the track session the pedal would drop. I would readjust and all was good again. I followed the advise of local spec Miata guys and gutted the parking brake stuff inside the caliper. Problem solved!
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