I drive an '83 F-100. I recently took it in because the steering was wandering and asked them to check the brakes while it was there. They found many things wrong, including, replacing the radius arms, alignment, front brake pads, front brake rotors, repack wheel bearings, clean and adjust rear brakes, & flush the brake system.

My problem is that the brakes were worse after they did all that they were when I took it to them. Now, the brake pedal sinks to the floor before it starts to brake and even then I have to stand on it just to slow down. They're telling me that they think that it's the master cylinder or the power booster.

My question is, since I wasn't having a problem with the brake pedal sinking before they did all that work on it, what are the chances that they screwed something up while they were working on it? Or could this just be a fluke that the sinking brake pedal showed up right after they did all that work?

Thanks.

 

Well, it's definately the master cylinder, and not the booster.

What probably happened is when they bled the system, the pedal got pushed down a lot farther than it ever had been before. With the water that was in the system (the reason it needed to be flushed) part of the master cylinder bore got corroded. It was never an issue before, because the seal never got pushed down that far into the cylinder. When you bleed brakes, the cylinder about bottoms out, and the corrosion tears up the seals, causing them to leak.

My two cents, is that given what you paid them to do all that work, they should replace the master for you for free.

 

I would recheck the adjustment on the rear brakes first.

 

Incorrectly adjusted rear brakes can cause a low pedal. They can't cause a sinking pedal. When the pedal sinks, it's always a hydraulic problem.

Although I should have added that it would be a good idea to make sure there are no leaks anywhere in the system at either the calipers or wheel cylinders. Make sure all the bleed screws are tight, too.

 

My brake guy always told me to put a brick under the pedal to limit travel for the reason that Andym alluded to. The thing that throws me is "and even then I have to stand on it just to slow down".I would check the Vacuum booster's check valve and vacuum line. After having major break work performed it amazes me that any shop would let it out in that condition. I'd be complaining at their busiest time.
Good luck and let us know what happens.

 

sounds like it may have an air pocket that was not bled out, we bleed off all systems with vacuum now because some systems have high spots so when you try to bleed it the air comes part way down to the bleeder then gets sucked back up and it will not come out. we don't have this problem anymore.