I topped off the fluids in the reservoir but the brake pedal is going down to the floor

Tiny
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  • 2013 FORD EDGE
  • AUTOMATIC
  • 60,000 MILES
I just installed pads on all four wheels of the vehicle listed above SEL model. The caliper cylinder came out of one of the calipers and I lost fluid. I was able to reinstall the cylinder into the caliper and replace the seal. I topped off the fluids in the reservoir but the brake pedal is going down to the floor. Please advise.
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Wednesday, March 14th, 2018 AT 4:32 PM

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Tiny
CARADIODOC
  • EXPERT
You have created multiple problems. First of all, there is going to be air in the caliper the piston came out of. That will have to be bled out. The bigger problem is between bleeding, or just running the brake pedal to the floor, the master cylinder has likely been damaged. Crud and corrosion build up in the lower halves of the bores where the pistons do not normally travel. Pushing the brake pedal all the way to the floor, when bleeding improperly, or when surprised by a sudden leak, runs the rubber lip seals over that crud and can rip them. That can result in a slowly-sinking brake pedal, and that often takes a few days to show up. Whenever a conscientious mechanic runs into a vehicle with a major leak, like a rubber flex hose or steel line, they usually automatically include a rebuilt master cylinder in the repair estimate rather than have to tell the owner later that more parts are needed than expected.

Another potential problem is when the piston came out of the caliper, a lot of brake fluid was lost and the reservoir may have run empty. If it was not refilled quickly enough, air will have gone down the lines. If the car has anti-lock brakes and air made it down to the hydraulic controller, it usually requires a scanner to command the ABS computer to open two valves so those chambers can be bled.

My last concern is why did the piston come out of the caliper? That usually only happens when worn pads were grinding on the rotor and were ignored for too long. Another potential cause is someone machined that rotor previously and cut it well below the published legal minimum thickness. Mechanics will not risk their reputation and a lawsuit by doing that, and if a rotor is machined at an auto parts store, they will not go below the legal limit either. New rotors are very inexpensive compared to a couple of decades ago, so there is no reason to not replace them when necessary.

If you do have to replace the master cylinder, it will not hurt to push the brake pedal to the floor, but it is a good habit to get into to never go further than half way. It takes about a year for that corrosion to build up inside the bores to the point it can cause a problem.
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Wednesday, March 14th, 2018 AT 5:33 PM
Tiny
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Thank you for the quick response, much appreciated. I was actually trying to help out a friend and was hoping it would be as simple as changing parts. You are correct, he had been driving the vehicle for at least a week with metal to metal. The right rear inside pad had absolutely no meat left on it whatsoever. That was the caliper that had the bleed. The seal did not appear to be torn or rotted but was no easy task getting it wrapped around that piston. It would make sense, unless I am totally off track, that there is a bunch of air in those lines considering the amount of fluid that bled out compared to the small amount that brought the reservoir back to full. What would you think should happen at this point, bleed and refill? Worst case scenario, bleed, refill and master cylinder replacement?
Thank you.
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Wednesday, March 14th, 2018 AT 7:11 PM
Tiny
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Ford uses very soft metal for their rotors. That makes them real quiet under normal conditions, but by the time you hear grinding, it has been going on for a while. Be sure that rotor got replaced. There is not much material left to work with to begin with, and there definitely is not enough left to allow them to be trued up on the brake lathe once they have been grinding.

First, fill the reservoir, then open the bleeder screws on the calipers that could have air in their lines. Loosen the cap on the reservoir so no vacuum builds up in it that would impede bleeding. Let the lines gravity-bleed until you see no more air bubbles, or until nice fresh, clean brake fluid is dribbling out. If you have to speed it up with a helper, be sure they never push the pedal over half way to the floor.

By the way, there is a special pliers, in two sizes, made for grabbing and expanding the dust boot on the calipers so the pistons can be easily dropped in. I taught my students to blow the boots up with an air nozzle, but the caliper has to be on the workbench for that. That is not a procedure we are likely to do today, but it was a common part of every brake job in the 1980's. I had to do it three times in my ten years at a new-car dealership in the 1990's, and I was the only person there who knew how to do it. It is a skill I wanted my students to have in case a caliper rebuild kit was the only thing available to get a customer back on the road.

If the car has anti-lock brakes, do not panic if you never get a good, solid brake pedal. You will likely need to find a mechanic with a scanner that can access the ABS computer so those two valves can be opened while bleeding.

When working with brake fluid, always be extremely careful to not get any hint of petroleum product mixed in with the fluid. That will lead to a very expensive repair. Professionals even wash their hands with soap and water before handling parts that will contact brake fluid to prevent contaminating them with fingerprint grease.

Once the air is out of the system, if the brake pedal sinks slowly to the floor when you hold moderate pressure on it, expect to have to replace the master cylinder. I have a trick to make that job easier so you do not have to bleed at the wheels. It works real well on all other car brands that have two steel lines leaving the master cylinder. The engineers at Ford complicated the procedure by using four lines on most of their vehicles, but the trick can still be used. I am about to lose my wireless internet connection. I will post that procedure later if it becomes necessary.
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Wednesday, March 14th, 2018 AT 7:58 PM

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