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My 1994 isuzu 250 brake went hard i replaced the pipes new booster new altenator with pump now brakes is better but when i am in traffic stop go after while no brakes please hel

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  • Isuzu Master
  • 20,706 Answers

No country stated, no car stated.
no engine stated, petrol or diesel.
below is my wild and useless guess ,its petrol.
Power assist brakes work off a base of manual brakes.
my wild guess 2 is KB truck, in Africa

this next line means with booster off line
(hose plugged, and pulled)
do the base manual brakes work or not.??????????????
this is first. and a big safety issue.
is this hard to understand.?
is this your first brake job?
how the manuals work 101:
using up to 100 lbs of (man) force on the brake pedal; can get you 600 psi force at the rear of the mc, (and 4 time more at front calipers)
the pedal is 6:1 ratio, (approx)
the MC piston to the slaves (ratio) the front caliper pistons are huge (4:1), and 6x4=24:1 total . 24x100 is 2400 lbs, from you foot to pads.
the cars stops great like this.
assist only lighten the pedal load, needed.
allows 50 lb girl to drive car, or my pet chimp.
or old skinny grand ma , to church...

these facts are why the brakes still work in manual mode.
The stopping distance does not decrease with boost.
(granny excepted) one could call this granny assist.
see, in a shop full of men we can stop the car
fast and same low distance.
my guess is your post is about assist only.
not brakes dragging
not braKES WEAK.


assist is a whole other set of issues, if only assist fails....see?My 1994 isuzu 250 brake went hard i replaced the p - 578fb15a-cb47-464a-8d9a-701f0cf1da4e.jpg

Posted on Dec 12, 2016

  • 1 more comment 
  • _-__-___-_
    _-__-___-_ Dec 13, 2016

    the (ASE 101) the mc to slave ratio
    is the area of a circle, of mc and slave pistons.
    pi x radius squared.
    so 1" or 2" pistons, (a wild guess)
    is ratio 4 to 1, mc to slave (area)
    so 4 x 600 is 2400 pounds per square inch
    like to say the front pads. huge. forces
    learning this one fact on the manual side of brakes, makes diagnosis vastly more easy
    no,
    this allows you do go, nero thumbs up or down. IN 1 TEST.
    if confused find a good car.
    then kill the vacuum to the booster.
    with out causing vacuum leaks.
    or stall the engine, coasting on a back road
    with no cars, people. KILL THE ENGINE,
    VACUUM GOES DEAD, AND THE BOOSTER HOLDS
    INSIDE 2 STOPS. (VARIES)SO PUMP THE PEDAL
    TILL THE ASSIST END,S AND LEAN WHAT MANUAL BRAKES DO FOR THE FIRST TIME.
    learn how manual brakes work. first
    by feel. you will not forget this.

    in the old days, with points ignitions 1960
    they stalled all them time or the choke stuck on and stalled.. about every 10,000 miles.
    so every one knew then what manual brakes where. fast. (today , seems nobody does)?
    go figure...
    only takes one time and you never forget it.
    I taught my kids and wife how to drive
    with brakes booster dead, and power steering
    too ,so they dont panic. (know your machine)
    on one car I had , 1964 Pontiac GTO, it took 2 feet to stop the car booster dead, (a bad design IMO) (after the bleed down) omg...
    end brakes 101. we can do more.
    all my japan cars the check valve is in the booster. (inside)
    it can fail open or clog.
    open causes instant , assist failure at stalls.
    clogged kills assist at all times.
    easy no?

  • Anonymous Dec 13, 2016

    is it a diesel?, why must we guess all this.
    if a diesel they have no vacuum.(old cars)
    so have and auxiliary vacuum source (pump)
    if pump fails ,no vacuum. use a gauge and learn to trust your tools.

  • Anonymous Dec 13, 2016

    the impossible words you used is this
    "no brakes"
    elaborate that in details.
    pretend we cant drive it for you.

    if car will not stop with 100lbs of pressure on the pedal the manual brakes are bad.

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  • Contributor
  • 4 Answers

Vacuum pipe non-return valve probably leaking causing vacuum to disappear with more brake applications being applied when in traffic.

Posted on Dec 12, 2016

  • 3 more comments 
  • Klaas
    Klaas Dec 12, 2016

    Hi rob their is no nrv on the vacuum pipe

  • Anonymous Dec 12, 2016

    we can measure vacuum at the booster.
    using a Tee fitting?
    no need to guess, that.
    hand vacuum gauges work. here.
    20"hg vacuum is good.
    in Africa that is. 0.67 BAR
    did you set the new booster end actuator, to the correct lenght before booster mate up to MC?

  • _-__-___-_
    _-__-___-_ Dec 13, 2016

    here is a booster seen on many japan cars.
    Nippon origins.. or 1/2 this or that...bs
    the tip must be calibrated. (if seen present)
    if yours adjusts, then it's set wrong.!
    the boosters fit many cars, so must be set to your car,(the shop has special tool or specs)
    if you let that tip preload that MC piston
    DOOM !! happens.
    if you felt the MC balk at the booster mate up, DOOM.
    very very very dangerous to drive like that.

    examplehttp://www.fixkick.com/brakes/boost.jpg

    250 is your slang for....
    this, right?
    yah ,it's African KB 250
    made in the GM/Isuzu plant there.
    I'D BET. if not that, then WHAT
    we can not give accurate answers lacking
    real cars name
    and country
    the book on brakes match both.
    and boosters vary by ALL THAT.

  • _-__-___-_
    _-__-___-_ Dec 13, 2016

    if assist is lost (boost)
    then vacuum is lost. to it
    (plenum vacuum for petrol, and a vacuum pump on diesel bad)
    or you put in the wrong booster
    or failed to adjust the pin on the end.
    as seen here and above.http://www.fixkick.com/brakes/boost.jpg

  • _-__-___-_
    _-__-___-_ Dec 13, 2016

    the diesels use a pump like this. AUDI.2001
    see #6 , that is your only source of vacuum on diesel (that has no throttle plate)
    back in my time
    we had vacuum windshield wipers
    and they went dead at WOT
    wide open throttle.
    some car have vacuum chamber so you get more
    stops full assist on and engine stall.
    (imagine pulling a trailer down steep hill)

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