Hot Rods BRAKE PEDAL RATIO- WHY DIFFERENT FOR POWER VERSUS MANUAL.

To some this may be simple. But why the different ratio? does it mean that a manual master cylinder has shorter stroke, perhaps with a larger bore to move same amount of fluid? Can the same master cylinder be used with or without power booster? Thanks for you answers.

 

The main reason is leverage. You need a longer lever when there is no power ***ist.
Most booster mounted master cylinder s are different because of the push rod.

 

You have it just the other way around. A master cylinder used with power boost can have both a larger bore and less pedal leverage because the booster overcomes the additional effort required. The larger bore boosted M/C also delivers more fluid for a given amount of piston travel and does not need to move as far to apply the brakes.

Yes, a master cylinder could be used either power or non power, but may not be ideal in one or the other case, depending on the variables in a homebuilt car.

Ray

 

Thanks. I think your last sentence may help explain my current problem. Maybe wrong master cylinder.

 

The booster requires extra travel to take effect, but multiplies pressure. Therefore, to get a similar feel, the manufacturer applies less leverage on the power brake models. Usually by different holes in the pedal itself.

 

Thanks. I have homemade pedal and mix and match parts. I'll keep at it.

 

FWIW, I am using a power M/C with a shallow hole in a non-power application.

I used a shortened 1.5" or 2.0" dia., (I forget??), soldered on type copper pipe "cup-plug" with a hole in the center of it's end and peined it onto the rubber boot groove for a pushrod holder in case the M/C piston gets stuck and the pushrod try's to fall out. -- Wheee, long sentence!!.....

I also had to redo my stock pushrod's length so it could be hand adjusted, standing on my head under my dash.. Used about a 1/16" slop for my pushrod and M/C hole.. Had to R&R my M/C about three times until I got my needed/wanted pushrod slop... A real pain...

I am attempting to use a 1.25" dia. piston M/C for my homemade, "pdqCBB", 4-wheel disc setup.

If it is too big, I will swap it out for a smaller piston M/C and try again..

pdq67

PS, front homemade brackets for 1969 Camaro/Van, 2-15/16" single piston calipers and homemade brackets for 1980, Cad Seville e-brake calipers for the rear. Rotors are 13" and 11.75".. dia..

pdq67