Master Cyl. Pushrod travel

I'm about to fab up my new brake pedal and master cylinder mount and such.

How much travel do I need for the pushrod? From no brakes to full brakes? I am trying to figure out how much travel I will need for the pedal and figuring my angles and such for the pedal and arm pushing the rod all the way in. Is it different for all Master Cylinders? Or do I just see how far it goes, in and out?

Thanks from the tard!

 

BTTT for an answer.

 

you want full pushrod (piston) travel! especially with a dual master cylinder, it won't be able to save your ass when one side pops, unless you can push the pedal all the way down for that last little bit of brake action.

 

So I take it that its different for all MC?

 

The pushrod travel (how far you can push in the piston before it bottoms, with no fluid in the cylinder) for a dual m/c is usually longer than for a single m/c.

 

With no fluid in the master cylinder, push the pedal in all the way until it bottoms out, and measure how far it comes back out again. I think usually manual brake pedals have about a 6:1 leverage ratio. So the pedal moves 6 times as far as the master cylinder travel. When you design the pedal, you'll need to know how far the pedal is going to travel so that it won't hit the floor or something before the master cylinder bottoms out.

When I designed a few pedals, I measured from the pivot point of the pedal up to the center of the pedal pad (not to the very top of the pedal pad). Like if it's an old Ford type round pedal pad that screws onto a bung on the pedal arm, I measure up to the center of the bung where it screws on. Then the ratio of that measurement to the distance from the pivot point to the center of where the clevis or rod end of the arm that connects to the master cylinder should be around 6:1.

It's easier if you can sit in the car and put your foot where you want the brake pedal to be, with the brake pedal pad hitting right in the ball of your foot. Usually your foot rests at a slight angle to the side. So once you know where you want your foot to be then you can work down from there to design the rest of it. The steering column is sometimes right in the way, so you have to compromise a little.