03 7.3L F-450 BRAKE PEDAL GOES TO FLOOR

[CISCO]

replaced master cylinder,hydraulic control unit,performed bleeding process with ids,then manual bled hcu & all 4 calipers still no fixy. while driving vehicle brakes fine and when you come to a stop(while pushing on the pedal)it goes down in increments of 2 until it reaches the floor & somtimes it just goes down all the way slowly. it seems to work fine if you push on pedal hard while going anything above 1 mph. need help thank you.

[Brad Clayton]

Clamp off all the brake lines at the front calipers and rear axle and see if the pedal holds. This will help you isolate the source of your low pedal.

[Aaron]

Service brakes all working OK? Sliders and junk all free, allowing movement where need be?

[Bruce Amacker]

Because it acts OK under hard pressure but drifts under light pressure, it sounds like a bad MC leaking past the seals. Remove the lines from the MC, install flare plugs of the correct size, start the engine and push on the pedal, both hard and very soft, and gently pump it without removing pressure from the pedal. It should not budge more than 1/8-1/4" at all. I keep a variety of flare plugs in my box just for this test, they are available at FLAPS and hardware stores.

 

Good Luck!

 

[mchan68]

Clamp off all the brake lines at the front calipers and rear axle and see if the pedal holds. This will help you isolate the source of your low pedal.

Do you quote a new set of flex hoses into the diagnostic process, if approaching the concern by this method?

[lmorris]

I do beleive that is a normal characteristic of those trucks. Any 7.3L with hydroboost I ever drove did that. As long as you get a nice pedal while braking and it only fades when completely stopped it is normal. Something to do with the hydroboost. Never did find out why, but we were always told it was normal.

[BrunoWilimek]

I read about this issue in a trade magazine and they also said it was normal. They found the cause to be a certain amount of flex in the calipers. If the brakes work normally, then it is not a performance issue.

[CISCO]

okay found very slight leakage on hcu but lines were tight, so i loosened them and retighten them and re bled every thing again as posted earlier. road test rechecked hcu not leaking but not truly convinced this is the fix. i road tested again,vehicle brakes fine,no safety issue with vehicle not braking and causing an accident. was not trying to pushed on peday like a crazy maniac so i let it go before i read all you guys is post this morning. praying it doesn't come back. i thank all of you for the help i will keep in mind all of the above replies. will be getting some flare plugs as Bruce mentioned sounds like a good idea. will keep you guys posted if it returns,again thanks this is an awsome crowd.

[Jim Warman]

There is a process for checking for a concern with the HCU - check the symptom chart in the brake section. Also, I recall an SSM from years ago regarding a condition called "step through". Might be worthwhile running OASIS to see if it is still in the system.

[Alex Bruene]

I seem to think it's normal too.

[Aaron]

You can push the brake pedal in my 08 to the floor when stopped, you can kinda push it past the hydroboost/master.

 

The truck will come to a complete stop with less than 1" of pedal travel though, so I don't lose a whole lot of sleep over it.

[CISCO]

OKAY TRUCK IS HASNT CAME BACK AND I DO TOO FEEL (AFTER READING REPLIES)THAT IT WAS NORMAL BRAKE PEDAL ACTION.

JUST INSTALLED HYDRAULIC CONTROL UNIT IN A 03 6.0 F-450 FOR ABS MOTOR INOP(OPEN CIRUIT CODE). INSTALLED HCU, PUSHED ALL 4 PADS WITH SCREWDRIVER,BLED WITH IDS ABOUT 4 TIMES PEDAL DIDNT SEEM RIGHT SO I MANUALLY BLED TWICE(STILL NOT SURE IF COLLAPSING CALIPER PISTON IS BETTER THAN MANUALLY BLEEDING ALONE),ROAD TEST AND IT WAS PERFECT.