97 F150
Is it always the master cylinder when the pedal goes to the floor and you have to pump the brakes to get pressure?
Thanks!

 

not always a blown line would do the same thing. blown leaking caliper and a blown leaking wheel cyl. could have same effect also.

so the question is are you losing any brake fluid anywhere?

 

no not losing any fluid
what about vac assist device?

 

if a vacumm brake booster fails the pedal is ussually real hard to push. but a brake booster failure shouldnt cause the pedal to go to the floor.

a simple brake booster test is to turn truck off pump brakes until pedal is real firm. then start truck with foot on brake pedal and it should go down alittle but not to floor. that will tell you if the booster is working.

does it allways go to the floor when you try to stop? only when you stop fast? we need more info. your problem is sounding more like a master cyl. then anything else though.

 

If I hit the brakes the pedal goes almost all the way to the floor, but it still stops.
If I pump up the brakes as I am stopping, I get pedal & pressure.
If I pump the brakes and hold them the pedal stays put.
When I pump the pedal to stop I feel the pedal pulsate. I believe this indicates the need for turning the rotors, new rotors or both. I guess there is also a chance I may need new calipers?

 

I would try to bleed the brakes first. A bad master will give you a pedal when you pump it but will still tend to fade when you hold the pedal down ( bypassing ) Air in the system can cause the symptoms you described and a good bleeding is simpler and less expensive than a new master. If it dosen't help your looking at a new master and bleeding them agian anyway so a little pratice won't hurt LOL.

 

OK, Thanks.
I'll try it.

 

im wondering if you might have some false abs activation going on. if you have a 2wd and the front wheel bearings are loose enough it can cause your abs to activate if you have 4 wheel abs. the brearing play can also cause the pulsation in the pedal.

and if your have rear drums they can be out of adjustment enough to cause a low pedal and brake pad wear can cause low pedal also.