M/C question for manual brakes

[brownz]

I have a 1970 nova that iam doing a budget build on and got some 2in drop spindles with 81 malibu rotors and s10 single piston calipers. i want to run manual brakes and not sure if i should go 15/16 or 1'' bore for the master cylinder. I want to go with a willwood master cylinder and adjustable pv. and any rec on what valve to get? I want a good one. because i also need for for my other project.

Thanks

[Apogee]

It sounds like you're running the low-drag, small metric GM-calipers. Those calipers' seals were redesigned to retract the piston further into the bore upon release to reduce parasitic drag and improve fuel economy, necessitating more volume than other older but similarly sized GM calipers with respect to piston area. Ideally, you would running a quick take-up, stepped bore master cylinder like the vehicles that were equipped with those calipers did.

Tobin
KORE3

[brownz]

It sounds like you're running the low-drag, small metric GM-calipers. Those calipers' seals were redesigned to retract the piston further into the bore upon release to reduce parasitic drag and improve fuel economy, necessitating more volume than other older but similarly sized GM calipers with respect to piston area. Ideally, you would running a quick take-up, stepped bore master cylinder like the vehicles that were equipped with those calipers did.

Tobin
KORE3

so what can i use on my 70 nova? can i use a willwood master cylinder?

[brownz]

this might be harder then i thought..

[Apogee]

I don't personally know of any stepped bore MC's offered by the aftermarket, only OE applications. You might take a look at the third-gen Camaro unit (the aluminum units, not the early cast iron ones). There have been several write-ups on the web using the first-gen S10 units, but those need to have the registers machined down to the car standard of 37.5mm [1.476"] in most applications.

Can you use a straight bore? Yes, you can. You just won't get quite as good of a pedal height and feel as you could from a quick take-up unit. If you go with a Wilwood, I'd start with a 1" bore unit and see how you like it. There are some non-Wilwood 15/16 and 1-1/16 options if you feel the need to go one way or the other. You can pick up a 1967-1976 1" bore Corvette manual disc/disc MC for cheap and take it for a test drive. It's a cheap way to figure out if the bore size is going to work for you personally before you go and drop $200 on a Wilwood unit.

As for proportioning valves, you've basically got the OE replacement disc/disc options, or the aftermarket adjustable options. I personally prefer the adjustable units myself, however both can be made to work quite well.

Tobin
KORE3