temerling

Hey guys, so I just picked up a 1997 F150 with some brake issues I am hoping is a fairly easy diagnosis and fix. With the truck running, the brake pedal will automatically go all the way to the floor and lock the brakes up. No apparent fluid leaks. Brakes still seem to work fine, I used a bungie cord to keep the pedal up on the drive home with no issues stopping.

At first I was thinking brake booster, but I'm not sure. What's the likely cause here and how can I test each brake component to rule out the faulty part?

screamineagle

Your master cylinder is shot. It's likely leaking fluid into the booster from the rear of the master cylinder, that's why there is no "visible" leak. Drive it enough and you will see the fluid level drop.

Edit: That is, if the pedal will stay firm with the engine not running.

temerling

If I shut the engine off the brake pedal is firm AFTER pumping it 4-5 times. Also, not sure if it makes a difference but after messing with it for awhile I think a better way to describe the issue is that the brake pedal stays wherever you push it to when you apply the brakes. It won't go to the floor on its own.

djfllmn

iTrader: (1)

Master cylinder is junk

temerling

Thanks for the help guys, will put a new one on tomorrow and see if it fixes the problem

02_Black_On_White

make sure to bench bleed it if you didn't already know! Let us know if that was it.

screamineagle

I was just about to mention the bench bleeding. You beat me to it lol. Good advice 02

temerling

Glad you guys said something, never done this before...Will do

temerling

Well, I replaced the master cylinder. Definitely helped, the brake pedal returns almost all the way up now, but it stops just far enough down that the brake lights stay on. Doesn't feel like the brakes are rubbing anymore though...from a stop, if you let off the brake the truck will move under it's own power on flat ground. Any thoughts on what else might be going on?

I never did check the front brakes before replacing the master cylinder though, and apparently there was no brake pad left whatsoever. I drove the truck for the day after replacing the master cylinder to test it out, about 100 miles, and that was enough to eat up the rotor so will be doing a brake job after work tonight. Rotors had a decent amount of surface rust, so the truck probably sat for a while before I got it. Going to clean and grease everything up when I put it back together so hopefully that will help. Still need to take a peak at the rear...just hate messing with drum brakes.

me1234

Just make sure not to grease the pad area. That'd be really counterproductive lol.