Infamous Sinking Brake Pedal

[Fordfleet]

Hi everyone, new guy here.

I'm a known associate of Adrianspeeder. I'm the one with the military trucks.

Today's problem, my '94 IDI Turbo F350 FWD crew cab has the sinking pedal problem. Have isolated it to the front brakes by plugging the rear port on the master cylinder. I've replaced the master cylinder, the booster, the rubber lines and the calipers so everything up front is new. My research indicates the F450 master cylinder conversion could be the answer. I just want to know if I'm missing anything before I throw yet more money into this.

Thanks

 

[HankHill]

try adjusting your rear shoes and checking the adjusters themselves.

also check the wheel cylinders, mine are shot and my pedal sinks all the way down to the floor, so soft my rear brake lights wont even turn on, going to rebuild the rear brakes this weekend lol

also your rear abs valve could be giving you flack, did you bench bleed the master?

 

[Fordfleet]

Rear shoes have been adjusted. Replaced the RABS also.

Like I said, this appears to be a FRONT brake problem. Plug the front brake port and things are good.

 

[Cincinnati Guy]

Check your front lines for leaks, and check your calipers for seepage. Also verify if both calipers are working properly.

 

[argve]

Sounds like either a master cylinder (which you just replaced) or the fluid is going somewhere..... so the fluid has to be going somewhere.... that means that it's going out of the system somewhere between the master cylinder and the calipers. A common problem is the flexible lines that attach to the calipers.

 

[Fordfleet]

New front hoses, also.

Clamped off both front lines, had good hard pedal. Clamp only one line (either one) pedal sinks to just over an inch from the floor and stops.

 

[94turboidi]

Is it possible there is a little air that gets trapped in the front calipers?

 

[MUDKICKR]

Is it possible there is a little air that gets trapped in the front calipers?

if he installed the calipers backwards it can, the bleeder screw has to be higher then the brake hose.

 

[84TD]

if he installed the calipers backwards it can, the bleeder screw has to be higher then the brake hose.

yup, happened to me when I replaced both calipers took weeks to figure it out.

 

[adrianspeeder]

if he installed the calipers backwards it can, the bleeder screw has to be higher then the brake hose.

No, calipers are correctly sided.

I ain't got a clue on this truck now. Everything that could be replaced short of the hard lines, that show no leaking on a close inspection, has been done.

Adrianspeeder

 

[itsacrazyasian]

weird question, did you change the front pads too? I bought a set of cheapy Advance auto silver brake pads to throw on my truck while i waited for some new Raybestos rotors and pads to come in from my wholesale parts place. I never opened the hydraulic system but the truck didn;t want to stop, soft pedal that picked up very low. The Bendix Fleet metallics that were on it before had a good pedal all the way to the wear indicator.

 

[Cincinnati Guy]

Can you pump the brakes and get a firm pedal?

 

[Fordfleet]

New Napa pads same time as the calipers.

Front of the truck hasn't been off the jackstands since.

 

[Fordfleet]

Can you pump the brakes and get a firm pedal?

No

 

[Cincinnati Guy]

You either have a leak somewhere or you have air in the system still. If your lines don't leak and you have no air in the system its impossible to have a sinking pedal because your fluid don't compress.