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Pavlin Koev
Pavlin Koev, CERTIFIED TECHNICIAN
Category: Ford
Satisfied Customers: 3430
Experience:  17 YEARS HANDS ON EXPERIENCE, TRUCK&COACH TECHNICIAN LICENCE
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Brake pedal slows falls to the floorboard...new one..abs Unit

Resolved Question:

Brake pedal slows falls to the floorboard. Replaced master cylinder twice, new one installed a week ago, bench bled, had system bled by a local shop.. he was dumbfounded after I put on a new OEM master cylinder. I've read where the ABS Unit can start to allow fluid to bleed by and you lose pressure. No leaks, reservoir remains full.. worn brakes maybe? Front have been replaced.. back are probably pretty low.. but front always wear faster.. replaced those 2 years ago. truck only goes about 7K a year in miles. Has 130,000 on it total right now.. like the truck.. but this brake thing is for lack of a better word, "pissing" me off. Nobody seems to know the problem.
Submitted: 2 years ago.
Category: Ford
Expert:  Pavlin Koev replied 2 years ago.

Pavlin Koev :

Hi and Welcome to Just Answer! My name is XXXXX XXXXX I will do my best to help. do you have disc or drum brakes at the rear axle?

Pavlin Koev :

if drum brakes at rear, first thing to do is to make sure brake shoes are properly adjusted

Customer:

Disc all the way around

Customer:

let me run out to garage and check.. but I believe disc

Pavlin Koev :

ABS unit can develop internal leak, as it has dump valve built inside.

Customer:

yes.. disc in rear

Customer:

that's what i've read

Customer:

strong pedal at first to brake.. then it won't hold.. slowly goes down to floor

Customer:

plus with engine off.. the brake is firm and doesn't fade.. so m/c is ok I think

Customer:

2001 w/ 130K miles..

Customer:

any other ideas.. ABS was my next thought.. can i test it ?

Customer:

no light on the dash.. but w/ key on.. abs lights up.. so circuit is working

Pavlin Koev :

ABS unit on F150 is known for problems and leaks.

Pavlin Koev :

I have replaced many of them

Pavlin Koev :

so this is most likely better way to go, new from dealer is around 700 dollars

Customer:

bypass?

Customer:

light would be on all the time huh..

Pavlin Koev :

you can create plugs and plug lines coming out of the unit

Pavlin Koev :

only leave the onnes going in

Customer:

4 wheel abs or just 2 w/ this year?

Pavlin Koev :

but there is nothing else that can cause this

Pavlin Koev :

4wheel

Customer:

leave lines going in but plus those coming out.. brakes will still work

Pavlin Koev :

no, do this only for testing

Customer:

oh I see.. if it holds pressure or not.. similar to plugging the m/c to test it...

Pavlin Koev :

if you want to by pass you will have to buy and incorporate proportioning valve

Pavlin Koev :

as truck has a lot more weight at the front

Pavlin Koev :

and this will change when loaded

Customer:

ok.. i've heard alot about that too.. it's built into ABS unit?

Pavlin Koev :

the fastest thing to do is just to replace the ABS unit and you are back on the road

Customer:

ok.. I will plug and test first. to make sure it's the abs unit.. so this is a common thing on f150's..

Pavlin Koev :

yes, this is correct.

Pavlin Koev :

also make sure that push rod between brake booster and muster cylinder is properly adjusted

Pavlin Koev :

your pedal will go soft when engine is started

Pavlin Koev :

but it must stop 1/2 of it's travel

Pavlin Koev :

when you apply normal force pressing on the pedal

Pavlin Koev :

you do not have to press extreemly hard when testing it

Customer:

that's about right.. there's some play before brakes engage.. but there's still alot of travel left after that

Pavlin Koev :

some vehicles may have a bit softer feeling pedal

Pavlin Koev :

do drive test

Pavlin Koev :

if your vehicle stops normally then there is nothing wrong with the truck

Customer:

brakes seem to engage quickly with reasonable pedal travel.. then pedal fades.. won't hold pressure etc..

Customer:

oh.. measured push rod too before installing new m/c.. seemed right based on length to inside of m/c.

Pavlin Koev :

ok

Customer:

so this rod is ok to adjust then.. I turned it out a little bit.. not much

Pavlin Koev :

rod must touch master cylinder as muster touches booster body, it is like almost 0 clearence

Customer:

ok.. that seems how it is..

Pavlin Koev :

if you apply brake (without fording the pedal and keep it this way, doe struck moves forward?

Pavlin Koev :

sorry I mean without forcing the pedal

Customer:

it stops.. but then pedal fades and truck creeps..

Pavlin Koev :

when bleeding the brakes, do you have good pressure at each wheel?

Customer:

a shop bled them for me.. he said he bled them a couple times.. no air.. but no improvement in the fading brake pedal.. so he suggested new m/c .. did that.. no change

Pavlin Koev :

i suggest one more bleeding.

Pavlin Koev :

start with right rear

Pavlin Koev :

do not stop to bleed until good pressure

Pavlin Koev :

have engine running as you bleed the system

Pavlin Koev :

then left rear

Pavlin Koev :

right front and left front

Pavlin Koev :

with engine running you will have help from booster

Pavlin Koev :

and this will give better pressure

Pavlin Koev :

on the way to shop brake hard few times to activate ABS pump

Pavlin Koev :

or you can bleed it your self

Customer:

yah.. I pretty sure I can do the bleeding.. with help from a friend .. I will try this first.. the low cost approach.. brake hard first to activate the abs pump.. then bleed

Customer:

thanks for all your advice.. Pavlin..

Pavlin Koev :

You are welcome!

Pavlin Koev :

thank you for using just answer and have a Happy Holidays!

Customer:

I will accept of course.. then save our chat for reference.. you too Merry Christmas!

Pavlin Koev, CERTIFIED TECHNICIAN
Category: Ford
Satisfied Customers: 3430
Experience: 17 YEARS HANDS ON EXPERIENCE, TRUCK&COACH TECHNICIAN LICENCE
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