Master cylinder

ford
f250

#1

Does the master cylinder wear out after? I replaced my front and rear brakes. Flushed the fluid and bled the brakes but they still seem a little soft.


#2

After what?

Yes, the master cylinder will wear out. Or more precisely, the internal parts will. The casing can almost always be re-used with new internals. A simplified way of looking at a MC is to think of it like a syringe. There’s a rubber plunger that pushes the liquid when it gets pressed on - - in the MC’s case, it pushes the fluid into the brake lines instead of out the needle of a syringe. As the plunger presses against the brake fluid, the fluid then presses against the brakes and makes them squeeze.

Eventually that rubber breaks down and allows fluid to slip past it, which reduces the pressure on the brakes.

A good way to see if your MC is having issues is to start the car, and then step on the brakes until the pedal stops sinking (which should still be significantly before the pedal sinks all the way to the floor - if it does, you either still have air in your lines, or your MC is in really bad shape and needs to be changed last month). Then keep pressing on them and see if the pedal starts to sink further. If it does, that’s a pretty good sign that fluid is getting past the “plunger” in the MC.


#3

A worn master cylinder typically causes the pedal to slowly sink as the brake pedal is held down.

Old rubber brake hoses can expand and make the brake pedal feel soft.

It’s a good idea to flush the fluid every 2-3 years to reduce these problems.


#4

Does the pedal harden if you pump it? If it does you still have air in the system. If it does not, and the pedal stays constant and does not sink, and the brakes stop the vehicle well and the rotors and pads are good, then you have no worries.

If you did not resurface the rotors when you changed the pads, it may feel a bit softer than it did simply until the new pads “wear into” the grooves in the rotor surfaces. This should disappear in a week or so.


#5

the pedal harden’s when i pump it. I should also mention the truck has almost 204,000 on it. I just had major surgery a month ago. So I and the truck will be sitting for a while. Thanks will get on as soon as I feel better. I will also bleed the brakes again.Thanks as usual great help from everybody. I just felt well enough today to ask the question.


#6

That’s good news. It means it’s just air in the system.

Sincere best.


#7

When you bleed it, make sure that you close each bleeder while the fluid is still coming out under pressure. It works best if you attach a hose and run it to a bottle above the level of the bleeder. I like to use a clear hose so as to check for air bubbles.


#8

Make it easy on yourself and get a set of Speed Bleeders. They’re pretty cheap, it’s a 1 time install, and they make bleeding fast, easy, and a 1 person job.


#9

I too like a hose and a pee bottle 1/2 full of fluid. Once the air bubble burps out, any drawback when you pump pulls fluid back into the caliper rather than air.