How do I know if I have a bad master cylinder on my truck?

My truck is a '99 F150 XLT 4.6

I had the rotors turned and new brake pads installed yesterday.
When I picked the truck up the brakes felt like they had air in them.
The brakes were bled 2 times and that helped some, but there is still something wrong with the brakes.

I was told it was probably the master cylinder. I would like to know for sure how to tell if it is in fact the master cylinder. I cannot afford to buy the master cylinder and have it installed if it is not the problem.

Please help!!

Thanks in advance for your help.

Candy

 

After bleeding the system, clamp off all 4 soft lines. Depress the brake pedal, if it gets hard than starts to fall...you have a bad master.

 

Thanks, I'll have that done and let you know.

Candy

 

A soft or mushy pedal that eventually finds a spot and stops is not a master cyl. A pedal that is mushy and keeps going down until it finally reaches the floor is generally a master cyl. Prob. not the best idea to clamp off the soft rubber brake lines. You can damage these lines easily and cause yourself more problems. If the system is not leaking then just pressing down on the brake pedal should tell you whats going on. Did you have this problem before the brake work. Sometimes new pads will take a while to break in and cause the brakes to feel ineffecent. ( like coaster brakes on a bike)

 

start the truck up
step on the brakes
put in drive(preferably where you might not hit anything)
hold the pedal down and give it some gas..careful gas is $$$ now
if the brake pedal continues to go to the floor i'd say its the master



if you dont have leaking brake lines

...zap!

 

Pestco1: Thanks for the info. The brake pedal didn't feel "mushy" before I had the brakes replaced......the brakes squeaked and the truck would "bounce" when I pushed the brake pedal.

 

If the problem is not the master cylinder, what else could it be??
I'm not comfortable with the way the brakes are now.

 

The soft rubber brake lines expanding under pressure will make it "musshy"/
Replace brake lines.

 

I suspect after reading your original post agian that there is still air in the system. ABS brakes can sometimes be difficult to bleed and get all of the air out. Maybe the shop didn't have a pressure bleeder and used the pump the pedal method. I have sometimes had to have the engine running so I could use the extra push of the brake booster to get a good push on the pedal and help get the air out. If it is uncomfortably soft have them bleed them agian.

 

When I had my little brake catastrophe, this was one of the signs I was having. In addition to needing new hardware, I was told that the "mushy" feeling was because of the rubber seals. They replaced the seals along with the hardware and the thing now brakes like it's a brand new truck.