Master cylinder bore size.

[winr]

1/2 ton truck.

Front disks, rear drums, manual brakes, proportioning valve.
Dual master cylinder with a 1" bore.

What problems if any if you used a master cylinder with a 15/16" bore.


Thanks.

Richard.

[xenginebuilder]

1/2 ton truck.
Front disks, rear drums, manual brakes, proportioning valve.
Dual master cylinder with a 1" bore.
What problems if any if you used a master cylinder with a 15/16" bore.
Thanks.Richard.

As a guess, you will have a softer, more "squishy" feel, full braking may put the pedal close to the floor, or you may run out of pedal travel for full braking. Depends on the mechanical travel and pedal ratio you have now.

[sam-missle]

i think it is smaller dia. is more preasure.

[82 camaro]

I switched my car to manual brakes I had stock disc on front and wilwood four piston on the rear. With a 1 1/16 bore peadle was very hard to stop went to a 1'' bore it works great. with you having drum rears you may be fine with 15/16 bore.

[Speedbump]

Smaller master cylinder diameter = better hydraulic force multiplication = more force (pressure) applied at caliper or wheel cylinder = better braking, but it is at the expense of more pedal travel at the master cyl. As long as the extra travel is within the parameters of your mechanical linkage (no floorboard stuff) you will have more braking pressure at the wheel which can be good.

[Warpspeed]

One problem you may have doing this, is that if you lose one hydraulic circuit, the pedal may then go right to the floor. There may not be enough reserve fluid displacement to pressurize the other half of the system.

In other words, you may think you have a duel circuit braking system, but if one side fails you lose both circuits,

Try it and see. If you can unscrew one bleed nipple, and the pedal hits the floor, the master cylinder is too small.

Probably the simplest way to reduce pedal effort is to use a vacuum booster that has a higher force multiplication. Look for something off a heavy luxury car.

[David Redszus]

Assuming that a force of 100lbs is applied to a 1" diameter master cylinder, the brake line pressure would be 127psi.

If the same 100lbs force is applied to a 15/16" diameter master cylinder, the brake line pressure woudl be 145psi.

It would take less pedal pressure to obtain the same braking forces. But your pedal travel will increase by 13%.

[winr]

Thanks very much for all of the replys guys!!


Richard.

[stealth]

Although you could always work with the pedal ratio a bit if need be too..