step bore master and pushrod

[speED]

I will be switching to a step bore master cylinder. The hole for the brake pedal pushrod is not your traditional depth.
Does anyone know how the brake pedal pushrod is supported on a step bore piston master cyllinder?
Is there room to drill into the piston in order to create a little more support?

Thanks
ED

[Apogee]

Okay...I'll bite. What master cylinder are you using? There are several quick take-up master cylinders to choose from, of which some were used in manual sytems while others were used in boosted systems. Or if you're not sure what MC to use, what are you trying to accomplish with your brake system, what calipers are you using, and what car are you working on (assuming you're running OE pedals)?

[speED]

67 Camaro
80 malibu/ monte carlo low drag front calipers
85 S-10 manual master
Dana 60 rear with c-clips
Using OE pedals

Tried using 68 Corvette master, result was a low pedal that could not lock-up wheels. MP Brakes has a link explaining
"Wrong calipers:If you are using a low drag or metric GM caliper without the correct quick take up master cylinder you will never get a pedal. In 1982 GM started using the smaller metric caliper because it's design retracted the caliper piston up to .125" ( a regular caliper retracts 2-4 thousandth's of an inch). This is a lot and without the correct quick take up master to move the caliper piston sufficiently your brake pedal will be extremely spongy."


ED

[Apogee]

Just because it's on the internet doesn't make it so. I think MP Brake may be exaggerating a little...1/8" of piston movement with a 3" piston would require .72" of 1.25" MC piston stroke...for each caliper. Somehow that doesn't sound like a good method to reduce pedal travel to me.

Using a feeler guage, I would say that the low-drag calipers retract the pistons about .010" when new. More than double what you call a regular caliper and significant in terms of the added volume requirement from the MC.

I'm sure you're already aware, but the S10 manual master has a 1.25" [31.75mm] primary piston bore while the power unit was slightly larger at 1.41" [36mm].

To answer your original question, it would appear that there is enough material to deepen the pushrod hole if you feel the need however I've only ever modified the pilot register diameter of the housings. I'm sure you could come up with a spacer to run with an extended pushrod in order to support it and make sure it couldn't drop out of the divot in the piston.

[speED]

The bore sizes for the manual master is 32mm for the initial volume and 24mm for the pressure.

[Skip Fix]

I pulled apart my extra 4WD Trans Am MC power brake and there is definitely enough meat to make it deeper. It's a 1 1/8 .

Having spun the wheels on my 78 TA and my 81 TA the low drag defiitiely are easier to spin.

[speED]

Skip Fix,
Your TA has a step bore master?

[Tito]

Skip Fix,
Your TA has a step bore master?

GM started putting the low-drag calipers on the '81 firebirds (and camaros?). I know the old '81 T/A I had had the aluminum master with stepped-bore M/C and low drag calipers. They also used a different booster to fit the larger OD of the stepped-bore M/C. I suspect that's exactly what Skip has on his '81...

[Skip Fix]

Yep 81 and has a BIG step. The TA 4WD 79s and I think the 80s still used the single step cast iron 1 1/8" MC like the disc/drums. but a dual diaphragm booster and no rear residual P valve in the MC.