Bad master cylinder?

[GLADESTEEN]

Yesterday on the way to work i felt the brake pedal go soft. It went about half way down during a normal stop. Throughout the day it did the same thing off and on. The pedal is not going all the way to the floor, but coming close. It still stops, but its concerning me.
It also doesnt do it all the time. Seems to happen at random.

I have checked fluid leve at resevoirl and it is good. I also looked for leaks and saw nothing. The brake fluid was completely flushed 10K ago, so i beleive fluid is fine. Truck has 120K and is a '93 F150 XLT.

I've read a few posts saying this could possibly be a bad master cylinder. Never changed one, but from reading they seem tricky with the pushrod adjustment, etc.. I looked on rockauto and saw a Dorman one for about $39 shipped. Not bad i guess.

Thanks for the help/advice! -Mark

[bluejay432000]

Just a change in the pedal level, but not really a change in the pressure required?

[GLADESTEEN]

Bluejay,

Yes, the pedal seemed to be "spongy" and just goes further down when im normal braking (sometimes). If i push hard, or pump the pedal when it does this, its right up at the top where it normally starts to brake.

[bluejay432000]

Originally Posted by GLADESTEEN

Bluejay,

Yes, the pedal seemed to be "spongy" and just goes further down when im normal braking (sometimes). If i push hard, or pump the pedal when it does this, its right up at the top where it normally starts to brake.

Yes, sounds like a mastercylender to me. Seals breaking down between resevoirs.

[GLADESTEEN]

Thanks for the help.

Are these symptoms for a brake booster failure also? If so, how do i narrow it down between the two? Maybe whats happening to me is typical of master cylinder failure only.......at least i hope so!

[bluejay432000]

Originally Posted by GLADESTEEN

Thanks for the help.

Are these symptoms for a brake booster failure also? If so, how do i narrow it down between the two? Maybe whats happening to me is typical of master cylinder failure only.......at least i hope so!

The booster failure would cause the pedal to be much harder. More leg pressure needed to stop.

[GLADESTEEN]

Thanks Bluejay.....really appreciate the help!

My choices from Rockauto are:

Dorman - $31
Cardone select - $33
Raybestos - $40
ACDelco - $51
Wagner - $52

Are any of these better than others, or is there a better place to look. None are remanufactured. There was a Cardone (reman) that was $21 tho.

[bluejay432000]

Originally Posted by GLADESTEEN

Thanks Bluejay.....really appreciate the help!

My choices from Rockauto are:

Dorman - $31
Cardone select - $33
Raybestos - $40
ACDelco - $51
Wagner - $52

Are any of these better than others, or is there a better place to look. None are remanufactured. There was a Cardone (reman) that was $21 tho.

I have no idea. I would probably go with a middle one, the Raybestos. I know that Raybestos and Wagner products are good. I'm using Wagner ThermoQuiet pads, and they are great. I have Raybestos front rotors and they have been fine.