Technical I just AIN'T happy with my brake pedal...

I have an "off-topic" hot rod that I installed front disc (GM "step" calipers) on the front and left the drum brakes on the rear. I used an S-10 master cylinder designed to work with the calipers.
It stops WAAYYY better than the old drum/drum set-up especially when roads are wet.
My gripe is...the pedal goes way down "almost" to the floor when the brakes are applied.
I understand/"they-say"....pedal height is determined by the rear brakes.
So what's the fix?!! Crank down on the drum adjusters and see what happens ?!
Thanx guys for your answers.......
6sally6

 

Properly set the rear shoe drag, and see what happens.

 

Step one is to make sure that the rear brakes are adjusted correctly. Back in 1962 when I was taught to adjust brakes it was tighten it until the wheel doesn't turn and back it off 11 clicks. That was on rigs without self adjusting brakes but I have always gone for the same feel when I adjust brakes and at one time I was doing at least a dozen brake jobs a week.

Second thing and maybe it should be the first is to compare the volume of your rear wheel cylinder with the volume of the wheel cylinder on the S-10 that the master cylinder was designed for and see if perhaps your wheel cylinders have a much larger volume. Simply meaning, with everything perfect you are having to move more fluid than what the S-10 MC was intended to move.

Example on an 88 S-10 a manual brake truck has a .875 rear wheel cylinder while a power brake truck has a .750 rear wheel cylinder.

 

Rear brake adjustment

new drums or have they been machined ? ( oversized?)

pedal height , adjustment , pushrod adjustment ?

to you have the “no drag” front calipers ? Possibly wrong master ?

correct bore wheel cyls for master ?

fire wall / under floor master ?

booster ?

 

What Mr48 said.

Ben

 

Do you have residual pressure valves in the master or in the brake lines? Especially going to the rear brakes. If not that may be your problem.

 

Pinch the rubber hose to the rear brakes and hit the brake pedal and find out if that’s even where your problem is.

 

Got me to think'in...... there (2) sizes of wheel cylinders (bore size) that will fit this Ford. ....
.90625 and .875.
I MAY have the bigger bore size cylinders on it. I changed them out MANY many moons ago soo I can't remember.
Would the .875 make a noticeable difference in the amount of pedal?! (I bet it would!!!)
Thanx Mr.48chev & others
6sally6

 

Is the master cylinder on the firewall or under the floor?

 

Firewall......?!
6sally6

 

Rear wheel cylinder diameter is a good point
Rear brake adjustment is a good point.
Brake shoe curve compared to the drum curve is a good point.

After all that has been checked and is OK and the problem is still there, the next question would be how much free play is at the top of the pedal before then mater cylinder starts to move? Maybe the length of the push rod between the brake pedal and the master is too short. Doesn't take much "extra" travel there to make a huge difference on how far the pedal travels before the brakes stop the car. .010 - .020 can make a big change on how far the pedal travels if the rod is too short.

 

If your master cylinder is pretty much flat you can Jack the front of the vehicle up and rebleed your brakes. sometimes an air pocket will get trapped in the back of the master and you step through part of your pressure.

 

^^^^^^^^^Aw-haa.....jack up the FRONT and any air might bubble up & out of the MC.
Interesting.
6sally6

 

Adjust rear brakes, had this same problem.

 

residual pressure
drum 10 psi
Dis 2 psi
In line