I have a '56 F100, it has A CPP kit to add disc brakes, and under floor booster/master cylinder. I used stock '79 ford rotors with GM calipers, and a stock '86 mustang booster,master cyl./prop. valve and '72 f100 drum brakes in the back. The master cyl., pads/shoes, calipers, and all lines are new. I have bleed the system 3 times, and have wilwood residual pressure valves inline front and rear(2lb&10lb). The brakes work ok, but I am unable to lock up the brakes unless I'm going really slow. The pedal takes almost no effort to mash to the floor. I am looking to firm up the pedal and get a little more in the way of panic braking ability. Is it a simple case of applying more leverage on the master cyl. than was originally intended? do I need to eliminate the prop valve alltoghter since this truck is way diffrent than a mustang? Any help or guidance would be greatly appreciated. Thanks, Matt

 

everything sounds right..

master below floor, requires residual valves.. got em. 2(disc) &10.(drum)
you will NEED a proportioning valve.. got it..
so.. does the vacuum booster work?
I installed a new booster on my beast and had no brakes... turned out the plastic check valve controlling the vacuum at the booster was bad.. brand new.
(ps.. off topic warning.. the morning I replaced that check valve, I blew the engine on the first attempt to start it after replacing the valve... be warned!!...).

once I replaced that check valve, all was well..

you can test i manually..

you should be able to blow into it from the booster side toward the engine,
but not the other way around.. (didn't work in either direction for me).
it holds vaccum in the booster.

you would get a soft pedal otherwise..

Sam

 

I know you said the master cylinder was new,but is the part number correct for a disc/drum system? Is the 2/10 lb res valves in the correct lines? Did you use rubber lines between calipers and frame lines or steel braided lines? Is there any slop in the brake pedal rod to master cylinder. Is this rod the correct length and diameter for the master cylinder you are using? Did you pressure bleed the system or other means? All items make some difference. chuck

 

Another thing to check is your lines, I had the same problem I even went to Midas and had them do the brakes with the same results. I checked all the brake lines and one was loose it didn't leak unless you pressed the brakes.

 

I manually bleed the brakes. I have the stock chevy pickup rubber lines in the front. I will check the vacuum check valve. The master is correct, it has the correct push rod, and there is no slop in the pedal. I have put about 1000 miles on this truck and I haven't noticed any leaks. I'll have to crawl under it, and see what there is to see.

 

have you got residual valves in line both front and rear ???? your master cylinder if it is still under the cab is below the level of the lines for and aft . the fluid will drain back down into the m/c and result in a soft pedal . the valves will hold pressure in the lines , and trust me make a BIG difference in the pedal , or ...... help me some one and forgive me , have you tried viagra ?????????????????

 

Would the location of these valves in the line, close to or far from the MC matter? Also, it almost sounds like there might still be an air bubble in the system, maybe trapt in the MC its self. Did you bench bleed the MC before hooking it up under the truck?

 

Slightly off topic, but I have basically stock setup, should I get residual valves, and from where?

 

I have a 2lb in the front line, and a 10lb in the rear line, they are very close to the prop valve, which is very near the master cyl. if that make a diffrence. I bench bleed the master cylinder before installing it.

 

"The pedal takes almost no effort to mash to the floor"
There has to be air in the line, somewhere, or the master cylinder is defective.
MC is a fairly simple check - disconnect the lines and plug the outlets. The pedal should be rock hard and not able to be depressed. If you can push the pedal down, fluid is getting past the piston.
Air in the lines - It takes a bubble smaller than a pin head to give you a soft pedal. FWIW, when you adapt systems the caliper may not be in the exact poisition as it was on the OE application. On our hot rod we cannot bleed the brakes normally. We unbolt the caliper, place a wood block where the rotor would go, shake them around, and bleed them with the bleeder straight up (caliper sideways). We spent 3 days trying to bleed them on the car, including using a pressure bleeder. (We also left one plug in the MC and bled 1/2 the system at a time, That's how we identified the fronts as the problem).
good luck

 

oldguy is right . you got prop valves inline and there seems to be air id start with what he suggested . old major my 53 is at present still equipped with the oe brakes and they made a big difference in my pedal " feel " . i put mine not to far away from the m/c . with the new system im gonna be putting on they will go on after the prop valve but relatively close to it and the m/c. at least thats what i gathered from reading , watching and listening ... just don't tell anybody i do those things , they might expect more from me if they don't think i'm a dumb a--!!

 

I also agree with Oldguy. The calipers could be mounted at such an angle to be impossible to bleed or they could be mounted on the wrong side, yes I have seen this done. Also make sure the rear wheel cylinders are mounted with the bleeder screws to the top.

 

OT to Oldmajor. If you still have drums all the way around, you should not need a proportioning valve. I converted mine to a dual mastercylinder a number of years ago and didn't need the prop. valve and the system works fine.

 

I will add that I have the caliper mounted level and on the correct sides as well as the rear cylinders in the correct position. I have also replaced the master cylinder since the truck has been on the road, and added the check valves, neither made much diffrence.

 

Is your brake actuating rod the correct length, allowing the M/C pistons to return completely? If not, the pistons can't draw fresh fluid into their bores.