I have a 94 F150 and when braking hte pedal wants to go to the floor( actually sucked to the Floor) and brings the truck to a rapid halt. Only way to control braking is put my foot under the brake pedal and lift up on it as I'm braking to brake smoothly, otherwise the truck stops right now. Once the vehicke stops the brake pedal returns to its normal position and the truck starts rolling. Have checked and bled the brakes. A complete brake job was down about 6 monthes ago. I wondered about the booster being bad. Any one have any thoughts?

 

ill try' maybe check the fluid level in your master cilyner located on the right side of your firewall. just a thought

 

Have you tried unplugging the vacuum hose from the booster and plugging it up and then testing the brakes? Does this happen also at idle? If you put your foot on the brake pedal, does it slowly bleed down to the floor at idle? Engine off? I had a seal go bad on the rear of the booster one time on a 76 Mustang and I couldn't figure out what it was. Turns out the seal around the pushrod had started to deteriorate and was leaking vacuum. I'm no expert but I would start looking at either the booster or the master cylinder. The master cylinder could be bleeding down or worn so as to let the fluid past the primary and/or secondary piston. How is your fluid levels? I have seen new wheel cylinders leak not long after being in service.(cheap made parts) Have you checked the rear wheels for signs of leakage?

Just some basic questions I'm sure others may ask.

 

The only thing that can cause something like that is the booster. Replace it and your problems will disappear.

-Joe

 

Maybe I should clarify the problem. The brake pedal is actually sucked to the floor and at times I have to put my foot under it to get it to come back to the normal position and release the brakes. Has made for some interesting experiences - go to lightly brake for a curve and the pedal is pulled to the floor and stops the vehicle right in the middle of the road unless I can get my foot under the pedal quickly and pull it up.

I have considered the booster.

 

As I already stated, that's a clear sign that it's the booster. The master cylinder is working properly if the vehicle stops. The differential valve inside the booster is shot. I don't know of any way to service the unit. Replace the booster and I'm quite sure all will be well again.

To confirm it, unplug the booster vacuum hose and cap it off, then take the vehicle for a very slow drive. You will lose all your power assist and will have a very difficult time stopping, but the pedal should not get sucked down to the floor without the vacuum assist.

-Joe

 

Thanks, will do that in the morning.

 

Second that. It has to be the booster. It sounds like it is working a little too well.

WV

 

Guys, thanks for all the input. Tried the vacuum line off test and the master cylinder is fine. Replacing the booster tomorrow and yes on a cold morning the pedal will go to the floor when starting the truck. Have to put foot under the pedal to bring it back up.

 

Replaced the booster today and the brakes are fine. Thanks for all of the input guys. can't learn enough about our trucks.