A year 1/2 ago my wife’s car (2008 Mazda Tribute) started acting funny.
The brakes started squeaking while driving, but as soon as the brakes were applied, the noise stopped. They also had a mild grinding sound. Not a metal on metal (aka no brake pads)…very superficial. Had to slam on the brakes and it activated the ABS (light did not come on) which caused the brakes to go to the floor.
Brought it in to the mechanic we always bring it to. They changed the pads and resurfaced the rotors. I KNOW they bought the cheapest aftermarket pads. I’m sure that and because the pads weren’t deglazed (I’m assuming they didn’t) is what is causing the noise.
Well…brakes worked fine.
Months later had to slam on the brakes again. Again, ABS activated (no light came on), brakes went to the floor. A day later it was still going to the floor.
Brought it back to the mechanic. They said nothing was wrong with the brakes, but they resurfaced the rotors. Brakes back to normal.
Happened again. Noises still there. Rotors resurfaced. I asked if the cheap aftermarket pads could be the problem. Of course the shop said no.
Brakes went back to normal.
Well, it happened again. Had to get on the brakes. and now they are almost going to the floor.
Brought it to a shop and they bled the brakes (not sure if they pulled the ABS fuse or not).
Brakes are still spongy and go down far, but not as bad.
Doesn’t appear to be the brake booster (put foot on brake while car is off and brakes depress when car is started).
Brought it to another mechanic (thinking it was the master cylinder) and he says he doesn’t think it’s the master cylinder, but an ABS problem.
The pedal going to the floor is never normal and it could mean your master cylinder is going out. The problem is that sometimes this failure is only apparent periodically. If it was my car, I will pay for a new MC installed and the system flushed and see what happens.
I’d agree w/my above colleagues. Replacing the master cylinder and replacing the brake fluid w/new is probably the best next step. I doubt the pedal going to the floor has anything to do with the pads or rotors, provided they pass a quick visual inspection by an experienced mechanic. I’d ask the shop to test the ability of the booster to hold vacuum too, just in case it has a leaky diaphragm. The squeaking could be do due the pads and/or rotors though.
Beyond that, there’s only a few things that can cause the brake pedal to go to the floor. These are the ost likely
Air remaining in the system … do a pressure bleed.
The brake fluid is boiling… check for stuck calipers or wheels that get hotter than others after a drive.
Faulty ABS system … requires the proper test equipment – make sure the shop you’re working with has it – and access to the proper factory service manual procedure.
Rater than accepting “no problem found” each time why not demonstrate the condition to the technician? I suspect the operation of the ABS system is normal, it is normal for the brake pedal to drop a little when the ABS system engages. In my experience “to the floor” is misunderstood 95% of the time. Customers are unaware of the full pedal travel, there is usually 4-5" more travel beyond the “to the floor” claim.
Just curious why the pedal would drop when ABS activates. Isn’t an ABS activation just like pressing on the gas pedal, but only briefly, on and off, and on certain wheels? Why would that affect the pedal position?
Make mine another vote for the master cylinder. It sounds like the MC is allowing passage of the fluid past the piston seals when hard pressure is applied. In your case the leak is not to the outside world but rather between the chambers in the MC. Ergo, you cannot see the leak but it’s there inside the unit.
Regarding the ABS, the light should NOT illuminate if the system is acting properly. The ABS light is there to warn you of a problem detected with the ABS system and only for that purpose.
Regarding the squeal, what you described a typical symptom set of wear indicators telling you the pads are low. It sounds like the shop fixed it when they changed the pads and resurfaced the rotors. Correct me if I’m misunderstanding your statements.
The ABS should not cause the pedal to drop. The ABS system introduces a solenoid-operated valve in the middle of each brake’s hydraulic line. When the wheel speed sensors detect that one wheel has stopped spinning consistently with the others it assumes the wheel has lost traction and stopped spinning, and the computer sends a squarewave to that brake’s solenoid-operated valve. That interferes with the hydraulic pressure and makes the brake pulsate rapidly, which can be felt in the pedal and often heard as a really horrible sound that scares the living bejesus out of most drivers unfamiliar with the sound. In this case, it’s the MC that I suspect is allowing the pedal to drop, totally irrespective of the ABS operation. The real connection here is that both are happening under hard braking for separate reasons, but making them seem related.
ABS system introduces a solenoid-operated valve in the middle of each brake's hydraulic line
Actually TWO solenoid valves and a motor driven pump. A valve closes to block the pressure to the skidding tire and another opens to allow the pressure to bleed off, closes and the pump applies the pressure again braking the wheel. The pedal can also drop a bit, but not “to the floor.”
If all parts of the ABS aren’t working properly, it could, indeed drop the pedal and introduce compliance into the system, if the accumulator (the spring-y thing on the right) starts to fail and hangs up in the bore.
I believe some models are equipped with drum brakes. If rear brakes shoes are worn or the shoes are out of adjustment on drum type brakes that can mimic a failing master cylinder.
Before spending money on a master cylinder I’d consider that possibility first; and which should have been considered already if it has not.
As to the squeaking that can also be caused by worn caliper slides which allow the calipers to vibrate along with glazed pads or rotors, missing anti rattle clips, and so on.
I would hope that in the repeated rotor machinging they have not gone under the minimum thickness recommedation.
There’s not a lot of meat on the bone so to speak on many rotors and two surfacings can really peel that down unless they were just brushing them a bit.