Mechanics

CHANGED FRONT PADS AND ROTORS, PEDAL NOW GOES TO FLOOR W/LITTLE BRAKING

2005 Ford Expedition • 75,000 miles

Firm pedal w/engine off.
Bled front brakes just in case. No effect.
Removed and reinstalled to insure installed properly. No effect.
Verified pads move freely. OK
Pumping pedal while braking helps some.
No fluid leaks can be found.

Ant Ideas?


Avatar
Tah2
November 24, 2011.



Did you check the slider bolts? Any stuck slider bolt would result in low brake pedal and inefficient braking.

If equuipped with ABS, go to a sandy stretch of road and test if the ABS works. After a few tries note if the pedal height increases.

KHLow2008
Nov 24, 2011.
Slider bolts move freely.
The brake pads engage, it acts like the system is not holding pressure. I thinking maybe the master cylinder or ABS getting some crud in them from compressing the calipers.
I'll try the sandy road trick.

Thanks

Tiny
Tah2
Nov 24, 2011.
No go on the ABS on the gravel road.
It will stop faster when the ABS activates on the gravel than on the pavement.
Master cylinder? All symptoms seen to point toward it.

Tiny
Tah2
Nov 24, 2011.
When pumping the pedal a few times, does the pedal height increases?

KHLow2008
Nov 24, 2011.
If I pump it fast enough, yes.
Pumping it slowly has little to no effect.
Slowly means depress, relase, depress. About 1 second between pump and release.

Tiny
Tah2
Nov 24, 2011.
Sounds like a faulty master, what dose it do if you hold soft pedal pressure? Dose it sink? And if you hold hard pedal pressure dose it tend to stay up further?

Mhpautos
Nov 25, 2011.
Soft pedal pressure goes straight to the floof w/no measurable decrease in speed (testing at around 20-25 mph so emergency brake will have effect if needed), panic stops have more response to input, just barely. Pumping seems to slow the truck best. If it is the master cylinder, what caused it? Everything worked fine except the pulsating pedal before changing the pads and rotors. I checked the new rotors and they are within.001" of the outer lip on the old rotors. I've worked on cars and trucks for over 30 years and have never encountered this scenerio. Any help would be greatly appriciated.

Tiny
Tah2
Nov 25, 2011.
When master cylinders are in poor condition, replacing the brake pads can cause it to fail.

Reason is that after replacement of the brake pads, the first few strokes would be empty as the cylinder pistons are pushed back in fully. That is the reason manufacturers recomends half strokes to push the pistons out. Depressing the master cylinder fully would cause it to fail as accumulated dirt inside the master cylinders would damage the already weak seals. Guess you would have to rebuild or replace the master cylinder depending on its condition.

KHLow2008
Nov 25, 2011.