Brake Pedal travel

[Howling.Wolf]

Hi, I wonder if this really a new topic , as I unfortunately didn't find a simular topic thru the search, sorry.

Ever since I have my truck I find that the brakepedal travel is veeeeeeeery long.
I estimate it is about 1/2 or even 2/3 of the entire possible travel.
Is that normal ?
If not, what can I do ?
I was hoping it would/could reduce it while changing the fluid and hoping of getting rid of some air, but wasn't the fact.
Fact is:
no air in pipes,
booster yes,
new fluid,
new brake cylinders (back),
it does start reacting (veryvery slight braking from the begin, but doesn't increase its break power for long travel).

Thanks for your ideas in advance.
Heinz
p.s. this is supposed to be spring

[Gary Lewis]

Heinz - There are really only 4 places the play can be:

Rear Brake Adjustment: After you replaced the rear wheel cylinders did you adjust the brakes?  That's necessary, and can be a big part of your problem.  I jack that wheel up just enough so I can spin it, and adjust it using a tool through the hole at the bottom of the backing plate until I can no longer turn the wheel by hand.  And then I hit the backing plate with a mallet to center the shoes and try again.  Once I can't turn it by hand I then back off the adjustment 10 clicks.  (Note that these trucks are supposed to automatically adjust the rear brakes as you back up and apply the brakes, but that mechanism doesn't always work well.)

Master Cylinder Adjustment: Between the master cylinder and the vacuum booster there's an adjustment rod.  If that gets changed when the master cylinder is replaced you can have a whole lot of slop.  I recently worked on a truck where someone had messed that up and the play in the system was awful.  But, it is a critical adjustment and if you go too far the brakes won't fully release.  I can get the dimensions for you later, but you get to the adjustment by taking the master cylinder loose from the booster and pulling the master forward.

Front Calipers: The pistons in the front calipers are sealed to the caliper by a square-cut o-ring.  That ring both seals as well as provides the "spring" to pull the piston back from the rotor slightly.  If the o-ring is bad it will let the piston slide back away from the rotor more than it should and then you have slop in the system.  To fix that you have to replace the rotors.

Worn Bushings: There are some plastic bushings in the brake linkage under the dash and they wear out and allow the metal of the linkage to wear.  Check to see if they are bad and if you need to replace them or even replace the linkage or build it up with welding.  You can see the bushings (#2471) in the illustrations here: http://www.garysgaragemahal.com/clutches-and-linkage.html

[Howling.Wolf]

Hello Gary,
again thanks a lot, I'll work my way through.
I will not be your first point, as this is done (adjustment of the rear brakes to the drums).

I'll check the rod but am concered as there is some very little resistance/pressure from the begin of the play.

I am working your points thrugh and let you know.

Thanx

[Gary Lewis]

If the rod is not properly adjusted there will be no resistance or pressure until the slack is taken up.  That's because you haven't yet contacted the piston in the master cylinder and aren't doing any work.

The rod is two parts - the part to the rear that is pushed by the linkage and the part to the front that pushes the master cylinder.  The parts screw together and you un-screw them to reduce the play in the system.

But, as said, that is a critical adjustment.  We guessed at it and that made a huge difference, taking the play out of the system.  But we went too far and the brakes weren't fully releasing.  So when driving they were dragging and getting warmer, which caused them to expand and drag more, getting even warmer - until they started smoking.  

I'll get the dimensions after while for you.

[Howling.Wolf]

Helo Gary,
just came back from the garage.
I tried your second proposal. And yes it makes a big difference if one adjusts the the rod.
But unfortunately itˋs been allright.
I also tried make it tighter but as you say the brakes cannot release proberly and after a while they pack up.
Well, however I‘ll go for your 3rd point/suggestion soon.
Have a nice day.

Heinz

[Gary Lewis]

Good luck!

[Howling.Wolf]

What is the width of the front rotor ?

[Gary Lewis]

I'll check tomorrow and let you know.

[Howling.Wolf]

Hi, I am a little frustated.
it is none of the mentioned Gary, sorry.
Any other ideas ?
Some of my German friends tell me, that this might be normal for American Cars.

Common guys U cannot let this sit on You

[Gary Lewis]

I had full intentions of getting you the info yesterday.  But I forgot.  Sorry.        

Dad's 1981 F150 4wd drive rotors are 11 11/16" in diameter.  And they say that the minimum thickness is 1.12".  And the 1985 book says the same for minimum thickness.

Is that what you need?

[Howling.Wolf]

No need to apologize, Gary really not, don't worry.
I am already happy of the help I already had.

Yes the thickness is what I want to look at.
I converted 1.12 inch into 2,8448 cm.

Thanks

[85lebaront2]

You might want to recheck that conversion sir. I get 28.448 mm, or 2.8448 cm, or are you using the European , instead of the . those of us in English speaking countries use.

[Howling.Wolf]

Hi,

jepp us 2.8448 cm equals iso 2,8448 cm.

Thanks

[Howling.Wolf]

Hurray it is fixed,
it was the Master Cylider as such.
Strange enough because it was dry, that is why i didn't thing of this one.
I got me one for $30 and replaced it.
Ahhh, what a great feeling having decent brakes again.
Now I fix the old one and keep it in spare.

[Gary Lewis]

Congrat's!