2001 Ford F-150 Brakes go spongy on shifting

SALTOUNIAN

MEMBER
2001 FORD F-150
V8
2WD
AUTOMATIC
127,000 MILES

My brake pedal tends to go spongy when shifting from drive to reverse and vice versa. Typically when pulling into a parking spot and backing up to straighten out. They occassionally do it when I have not applied them hard enough when leaving a place either. When I say spongy, it feels as though they go to the floor. After the intial time to the floor they will not do it again until I change gears(drive/reverse) again. There are no fluid leaks, the brake fluid was changed by the dealership about 20k ago. I have bled the brakes as well, with no air in the lines. Is this a vacuum issue? If so is it the power booster or the the other vacuum thingy next to it on the fire wall? When I pulled the vacuum line on the booster there was plenty of vacuum on it.

3 Replies

MERLIN2021

MECHANIC
17,250 POSTS

First thing to look at is the brake fluid, is it brake fluid? If oil or tranny fluid was added to brake fluid reservoir, the rubber inside the cap will swell, and not fit. Remove a small amount of the fluid, swirl it in a cup of water, any white oily beads floating in it? If yes, fluid may be contaminated. Next and the easiest, check rear brakes, could be low, or out of adjustment, either condition will give you these symtoms, if your parking brake works, push it down a few clicks, does the pedal improve? If yes, rear brakes need a look! Last, check the master for a swirling action when the brak is pressed and released, if no swirl, the compensating port is clogged.

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Thursday, August 13th, 2009 AT 1:19 PM

SALTOUNIAN

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1 POST

I believe it to possibly be the compensating port. I noticed this morning that when slowing down the pedal seemed to pop and go to the floor at a downshifting point. Does this information help in resolving the question? I know the rear brakes are fine. They are new pads and disc with about 10k on them.

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Monday, August 17th, 2009 AT 7:58 PM

MERLIN2021

MECHANIC
17,250 POSTS

With 127,000 it could be a bad master, or fluid passing by a caliper seal, it needs to have the dust boots around the pistons pulled back, exposing the piston under the boot, look for excess fluid in there.

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Tuesday, August 18th, 2009 AT 12:45 PM