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1999 front brake drag

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#1
havoc

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new ESR calipers all around(rebuilt fronts and no change), new ss brake lines all around, new proportioning valve, new master cylinder, pads are not binding, wheels spin great when cold, when hot front left has minor resistance and front right has major resistance, open bleeder valve on either front and fluid comes out, then wheels spin easy, brake pedal travel is a fair amount before brakes engage, not a firm brake pedal, brakes have been bleed numerous times, always use fresh SRF fluid, lots of kickback



#2
Steve Scheifler

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You said a lot of pedal travel, but to be clear, travel not just requires more force?

That part aside it sounds like the valve inside the brake booster may not be allowing the back side to get vacuum when brakes not being applied, allowing the vacuum on the front side to apply a little pedal. Or similarly something mechanically sticking in the pedal so it doesn’t fully release.
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#3
Steve Scheifler

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You didn’t mention if this started only with replacing or rebuilding calipers, or was happening before that. Had you run the car long without the problem?
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#4
havoc

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lots of pedal travel, not force, problem existed when I bought the car 1.5 years ago and after replacing everything. So are you suggesting to replace the brake booster and that may cure the problem? If it is the brake booster would it matter that the brakes don't have any drag at all when cold?



#5
Steve Scheifler

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Good questions but the best answers I can offer are all maybes. Given all the things you already replaced and assuming for the moment that they are good, there isn’t much left. Temperature aside for a moment, I can visualize ways that a sticky/leaky booster could cause both symptoms at least as described. But I’m at a disadvantage of not feeling it for myself and you are (I’m assuming) at a disadvantage of not having enough experience with a properly functioning system to be highly detailed in the differences.

As for the temperature, although not hot compared to the brakes the booster does get warm from being above the exhaust manifold. So if it’s acting up, sticky, whatever, that could get worse as it heats up and things expand.

This is all speculation of course but at this point given what you told us I would certainly be looking to borrow a known good one and give it a try.
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#6
TylerQuance

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You could try new caliper brackets only and see if your result is the same. I have seen them bend if you bleed brakes without the rotor seated square on the hub with a lug nut or 2. Not bent enough to see, but bent enough to make the car slow and taper brake pads causing a long pedal.

#7
Steve Scheifler

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You could try new caliper brackets only and see if your result is the same. I have seen them bend if you bleed brakes without the rotor seated square on the hub with a lug nut or 2. Not bent enough to see, but bent enough to make the car slow and taper brake pads causing a long pedal.


Good thought, worth a look though it sounds like this happens whether pads are old or new, and no mention of excessive taper.

Along the same lines, if this has old “optimized” spindles those can cause issues similar to bent brackets if not done correctly, and potentially get worse when hot.
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#8
FTodaro

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If your getting excessive pedal travel make sure that the pin is installed between the brake pedal and the brake master shaft. That will not explain the wheel drag but could explain the pedal travel. Had a customer with that problem and it scared me just to drive it onto my lift. On the wheel drag start with filing down the brake pads and use the brake hardware.


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#9
havoc

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Sorry,  I should add I am using Pagid pads and have filed down the tabs on a set with no change, using springs and clips, new or used rotors-no change, I also have replaced the brackets with new, in addition the spindle is new on the right side, the side with the most drag, new rotors and I always put a lug nut on the rotor, most of brake bleeding is done with a Power Bleeder, using Miatahubs as they are legal at the Autobahn CC

 

I will check for pin in pedal to master shaft.



#10
Tom Sager

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Good questions but the best answers I can offer are all maybes. Given all the things you already replaced and assuming for the moment that they are good, there isn’t much left. Temperature aside for a moment, I can visualize ways that a sticky/leaky booster could cause both symptoms at least as described. But I’m at a disadvantage of not feeling it for myself and you are (I’m assuming) at a disadvantage of not having enough experience with a properly functioning system to be highly detailed in the differences.

As for the temperature, although not hot compared to the brakes the booster does get warm from being above the exhaust manifold. So if it’s acting up, sticky, whatever, that could get worse as it heats up and things expand.

This is all speculation of course but at this point given what you told us I would certainly be looking to borrow a known good one and give it a try.

Also, the vacuum hose that runs from the booster to the steel vacuum tube has a check valve in it.  That hose needs to be installed in the right direction and that check valve needs to be working fully. 


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#11
havoc

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I just swapped that out with known working hose with the check valve, drew directional arrow before removing. Just drove car on track, definitely no change to Right Front. I don’t brake while exiting track nor on pit lane.

#12
havoc

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Brake booster NLA from Mazda, will have to assume a junk yard one was working good.

#13
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#14
havoc

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Are you suggesting to take it to the professionals?

#15
havoc

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Installed used brake booster, pedal felt better driving in paddock. Race test today!

#16
havoc

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Thank you Steve!!! New booster fixed the problem with the car!!!! Thanks again
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#17
Steve Scheifler

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Might be interesting to open the old one and see if you can tell what failed. I didn’t ask previously how long after shutting it down pressure remained in the lines. If a long time then more likely mechanical drag than a bad internal valve since vacuum would probably bleed off.
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#18
havoc

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I will when season is over, now to concentrate on perfecting handling. Thanks again




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