Brakes Getting Hard

#1

Alright so I’m stumped, I’ve been dealing with this issue all season and have been going nuts trying to fix it. heres what I’ve got so far;

The problem; The brakes will “Ice” up on me or lock me out where i will have to stand on the pedal to get any result. my dad and i swapped cars for a session and he nearly stuffed my car into a wall they brakes were so bad, and his brakes felt amazing! we are both running exactly the same brake setups and the cars are completely different under braking. His pedal is nice and firm with good modulation characteristics and mine is hard as a rock with no result or modulation ability. when i am on track if i back off on them on the cool down and then go to use them, they are much better, but not perfect.

What I’ve done to the car; I have rebuilt the calipers and there was no major scoring or pitting anywhere so i know the calipers are fine. The MC is new. The fluid has been changed several times throughout the season with no results. i have tried 3 different types of pads, front and rear, to see if it was a glazing problem. And i have even tried changing my braking techniques to see if that would change anything, like maybe i was jumping on them too hard or something and that didn’t change anything.

What i Know so far; It seems as tho the problem is one of two things, either a dragging brake causing the fluid to boil and give me hard brakes, or a failing booster not as siting me enough.

What I’m asking; If it is dragging brakes I’m looking for ideas as to what to fix or what is causing this problem. only thing i can come up with is bad calipers, but they have been rebuilt so I’m looking for more ideas. Also if it is a failing booster how do i check it, cuz it feels fine, i press on the brakes and turn car on, pedal drops. i pump pedal and stop with pedal pressed, let of slightly and press back gently and the pedal does not droop to the floor.

So there is everything i can think of right now. Please give me any and all ideas as i am open to anything and really need this fixed soon. I’m not sure how much longer i can race with zero trust in my brakes. Turn 11 at infineon is scary when your never sure if your brakes are going to work haha. Also I’ve been going through pads pretty quickly, about 2-3 weekends a set only on the front though and they are not wearing evenly. they were wearing worse but i did some work to the guide pins. they were wearing super bad with a huge taper from inner to outer, not its ever so slightly tapered from left to right, about 1mm diff in thickness.

#2

The usual complaint is brakes going soft. Are you saying that you can’t push the pedal in? That would probably be a serious problem between the pedal and the abs where the lines go their four seperate ways. I would suspect abs block or master cylinder. Is the problem random or does it gradually increase until you pit.

Are you saying the pedal feel is normal but your just not stopping. The would probably be a pad issue. When I’ve had this problem it means there is no pad left.

If the pedal feels soft and you have to pump the brakes it means the fluid is boiling. To much heat to the calipers or contaminated fluid. Drag would cause this.

You should be able to tell if you’re brakes are dragging by jacking it up and turning the wheels by hand.

#3

the pedal feels like I’m simply pushing against a brick wall. and the problem seems to always be there except or the first push and then again after i let things cool off. and i say the pads are dragging because they aren’t letting go completely, its not so much that i can’t move the wheel but it spins about 25% less than my other car which i know is right.

#4

I think dragging could only cause a soft pedal not a hard one. What your describing is not a common problem. Check your vacuum lines. Did you replace the master cylinder and not the booster? I keep thinking of a kink in a line. Maybe its possible a front soft line kink could be the problem. The front brakes do almost all the work but I’m not sure a kink in one front lines would make that much difference in pedal feel.

#5

It sounds like a sticking caliper(s). The extreme pad taper you described could cause binding. Is one side wearing excessively? Try a fresh set of pads and see if the problem goes away.

#6

It is easy to tell if you have a sticking pad. Just check the temperature at each wheel after a session. Typically you can do this with your hand. If one side is way hotter then the other that sides pad is sticking.

Places to look:

  1. Rear brake proportioning valve. If this has crap in it it will stop fluid from going to the rear.
  2. Brake booster. This is my bet. If it is old and original I would replace it.

When I first built my SE30 the car felt like it was never going to stop. A lot of that was adjusting to ABS after not having it on the previous racecar. I finally replaced the two items above and either fixed the problem or got used to it. They did make a difference so I feel they fixed the problem.

#7

I vote for ABS pump.

All it would take is for fluid to be getting to one caliper properly and the pedal would feel more or less normal. Braking power would be screwed, but pedal feel wouldn’t be too odd.

If it was the booster the pedal would feel harder, but the pedal wouldn’t feel “locked out”. IMO only a bad ABS pump can make the pedal feel “locked out” because only it can prevent all fluid movement in the system.

Used ABS pumps are cheap, just be certain to torch each plumbing connection before hitting it with a brake line wrench so you don’t screw up the hard brake lines.

#8

A bad booster will usually result in a stiff pedal all of the time. The most common booster failure is a leaking diaphragm, which will show up under a vaccum test. A bad check valve will cause normal or nearly normal pedal feel when the engine is at or nearly at idle, but a hard pedal at speed.

If the booster checks out, pull the ABS relay to disable the ABS. If the problem goes away the cause could be bad speed sensors, damaged sensor wiring, or a bad ABS module. The pump would be towards the bottom of my list if the brakes are normal when the car is given at low speeds.

#9

all very good input thank you, however;

I have been taking rotor and caliper temps all season on both cars a recording them, i have not seen any weird anomalies between the two cars. they are both running about the same temperatures. i can’t remember the number ooff the top of my head but its somewhere around 400-500 on the rotors.

I have changed the pads three times already and the problem persists, however with work to the calipers, i wear has gotten better

I thought about pulling the abs relay, but was afraid to as i heard when you do that, it changes the bias to the rear of the car. is this true? i don’t want to pull a relay and go on track and have a nice surprise.

The failing booster a good theory here, but I’m just not sure how to test it. i did pick up a Parts car this weekend, won nationals last year, its the TFB #69, and i will swap the booster over as soon as i can as well as the check valve. How could i check to see if the check valve is working correctly or not.

Also another symptom that may be relevant, the car idles around 1500rpm and usually when i pump the brake pedal, it will cause the idle to surge, not sure if this is normal or not.

Again, Thank you all for the input, i am looking for anything here!

#10

[quote=“Speedracer” post=60834]all very good input thank you, however;

I have been taking rotor and caliper temps all season on both cars a recording them, i have not seen any weird anomalies between the two cars. they are both running about the same temperatures. i can’t remember the number ooff the top of my head but its somewhere around 400-500 on the rotors.

I have changed the pads three times already and the problem persists, however with work to the calipers, i wear has gotten better[/quote]
This doesn’t sound like a caliper or pad problem.

Unless the ABS pump is bad disabling the ABS should have no affect or brake balance. That is controlled by the bias valve.

[quote]The failing booster a good theory here, but I’m just not sure how to test it. i did pick up a Parts car this weekend, won nationals last year, its the TFB #69, and i will swap the booster over as soon as i can as well as the check valve. How could i check to see if the check valve is working correctly or not.

Also another symptom that may be relevant, the car idles around 1500rpm and usually when i pump the brake pedal, it will cause the idle to surge, not sure if this is normal or not.[/quote]
Idle should not change when you apply the brakes. The fact that it does might suggest a leak in the booster. Once check for the booster is to pull a vacuum on the booster and see if the pressure rises when you stop pumping.

#11

Try pulling the vacuum line off of your fathers car and drive it to see if his brakes will feel the same as on your car. I’d they do, then you know your booster is bad on your car.

#12

i am going to try disabling the abs and see if it helps. i checked the check valve and as far as i know it is functioning properly, meaning it only allows air one way. I will try and change the booster before the track next weekend but i may not be able to with school. I am pretty sure it is the booster at this point or something in the ABS. When i pump the brakes the idle jumps up, when i do it in any of my other e30s their idle does not move…

And what do you mean by the vacuum line? are you referring to the line between the check valve and the booster?

#13

Bad booster will also yield hard pedal.

#14

Ok so here the update, tried disconnecting the power to the ABS unit and nothing changed, just got really hard for me to drive the car since i am not used to no abs at all. I have now finally been able to pull the car apart and really get in there and what i found was when i pulled the Master off, there was no O-ring between the MC and Booster. How many think this is the problem. It would explain why my pedal feel would return to normal after some time off the breaks, since it would give it time to build some vacuum.

I am still going to change the master and possibly the ABS Unit, but i can do that later since having the motor out doesn’t make it easier. Let me hear some input here guys!

#15

The lack of a seal between the master cylinder and booster can make for a hard pedal from the loss of vacuum. Much like when the booster diaphragm has a small leak.

#16

I had the same issue when doing a confidence tap of the brakes before full application. When applying the second time the pedal felt like it had a brick stuck behind it.
Replaced the check valve to the booster and problem solved. I also stopped with the confidence tap.

Chris