hard brake pedal

i've got a problem with the brakes on my model a sedan. you have to exert an ungodly amount of pressure on the pedal to get them to work. its got drum brakes all around and an using a 67 mustang drum brake master and proportioning valve. the pedal arm has been shortened about 3-4 inches. anybody got an idea as to what my problem might be? i realize that the shorter arm will make it harder but this is unreal. thanks in advance, bruce

 

you DON'T cut the pedal down on manual brakes.

 

Here is what you did wrong....

 

the car is channeled the width of the frame so i had to shorten it. what else could i have done?

 

the short pedal could be your culprit. ideal set-up is at least 7:1. Also, is your pedal angled to use all of your leg pressure?

 

If you can fill the hole where the rod goes in now and drill closer to the hinge point, if you can without going over center in the travel,or try finding a smaller bore master

 

Drum brake vehicles did not have prop valves. You may be confussing the distribution valve if taken off a donor car with drum brakes.
You have to maintain a 6-7 to one pedal ratio with manual brakes for normal pedal efforts. Sounds like you need to add a vacuum booster to go with your short ratio. Power ratios are about 3-4 to one.

 

I agree with RJP about the pedal ratio. Now what to do about it. You did not mention whether you have floor mount or swing mount. If you can change you pivot to get back to a 7:1 is one option. The other would be to decrease the bore size of the master cylinder which would provide greater hydraulic advantage but at the expense of increased stroke on the brake pedal.

Do you know the bore sizes of the wheel cylinders and of the mustang master cylinder?

 

i just researched the bore size on the mustang mc and it appears to be one inch. so if i went with one with a smaller bore like 15/16 do you think that would help? i believe the wheel cylinder bores are - front= 1 1/4 and rear 1 3/16.

 

It would definetly help, do that first than if you need more try drilling the hole a little closer

 

I have the same problem, but not nearly as intense as yours. I actually had to lengthen my (Wilwood hanging) pedals by about an inch, due to where the unit had to be mounted on the firewall. The ratio was originally 6:5, so it has to be more now. Anyway, I'm driving it & have gotten used to it, but you really can't lock up the brakes. With a light hot rod, that's probably a good thing. Still, I'd like to improve it. I'm really leaning to decreasing the master cylinder bore, which is at 1." I have rear drums, front discs, by the way. I don't have a proportioning valve (it's one of those Wilwood balance bar ste-ups), so I can blame it on the proportioning valve. There are so damn many variables when it comes to brakes & it sure is hard to get the right combination, especially when it's your first build.

 

seems like the first route to take per the suggestions given is to change the mc to a smaller bored one. what cars had the smaller bores?

 

I don't understand this, I used early Mustang brakes (pedal, fruit jar on fire wall, rear axle) in the car in my avatar which is channeled and I didn't cut the brake pedal....

 

the pedal ***embly w*** given to me by a buddy, didn't come from a 67 mustang and this is a dual resevoir not a jug type