Anyone know off hand what the front disk brake piston size was on a 68? It looks like a large single piston. I called wildwood about a manual master and he asked about the piston size. I'm not home right now. Anyone know?

hard to say- your 68 came stock with 2 (or was it 4?) piston calipers stock if it had disc brakes.
if you have single piston calipers, then it's probably a 69 setup, but could also be 78-88 G body "metric" parts if someone put drop spindles on it somewhere along the line.
pull a caliper out, take the pads out, and measure the piston with a tape measure to get a rough guesstimate of what you've got.

Thanks I got it. 2 15/16". Wildwood recommended a 1" or 7/8" bore master for the manual brakes. Not sure what to go with....:confused:

The smaller bore will create more line pressure.

The smaller bore will create more line pressure.


I'm worried about too much travel and not enough fluid with the 7/8" Think I'll be fine with 1"?

What brake pedal setup are you running? Hopefully the Wilwood tech asked about pedal ratio and disc size too.... without it, I don't know how they'd guess at the right master cyl.

Stock 67-69 brake pedal with the manual (upper) hole is about 6:1 for manual brakes (or so I've read). With stock front discs and calipers, I don't think I'd go any smaller than 1" bore master cyl. 7/8 would give lower pedal effort, but I think you'd run out of travel with the large 2+15/16" front calipers. 1" might be OK, but might be a little close. I think I'd start with a 1" at least...

-T

7/8" is too small. 1" is correct. The 7/8" will put your pedal very close to the floor board when you press down. Higher pressure, so what, less volume, more travel to do same amount of work.

What brake pedal setup are you running? Hopefully the Wilwood tech asked about pedal ratio and disc size too.... without it, I don't know how they'd guess at the right master cyl.

Stock 67-69 brake pedal with the manual (upper) hole is about 6:1 for manual brakes (or so I've read). With stock front discs and calipers, I don't think I'd go any smaller than 1" bore master cyl. 7/8 would give lower pedal effort, but I think you'd run out of travel with the large 2+15/16" front calipers. 1" might be OK, but might be a little close. I think I'd start with a 1" at least...

-T

Yea, I told him the size and ratio. Those are what he recommended. What year and car one should I look for? I've been reading corvette ones?

I'm concerned about how it stops though. Right now I have a 1 1/8 bore with a dual 8" booster. It didn't work good at all. I ended up moving it by using washers and lineing the brake rod with the upper hole. It stops good right now. I'm wondering how good it will be if I remove the booster and use a smaller bore. Would it stop the same?

Your 1 1/8 inch diameter MC is OE equipment size for disc/drum set-up, regardless power or manual.

your 1 1/8 inch diameter mc is oe equipment size for disc/drum set-up, regardless power or manual.


1 1/8" was never used on manual brakes. You will have to stand on the pedal in hopes of getting it to stop. 1" is correct.

1 1/8" was never used on manual brakes. You will have to stand on the pedal in hopes of getting it to stop. 1" is correct.

I know 1" is correct for manual. I'm wondering the difference from 1 1/8" power to 1" manual. Not sure if I'm going to like it.

Go with the 1 inch M/C . I tried the 1 1/8 M/C with factory disc and will stop but foot pressure is to high. Noticable difference with 1 inch. Stay away from 7/8 one. IMO Is there a reason going from power to manual?

Go with the 1 inch M/C . I tried the 1 1/8 M/C with factory disc and will stop but foot pressure is to high. Noticable difference with 1 inch. Stay away from 7/8 one. IMO Is there a reason going from power to manual?

Room for twin turbo headers and 3" downpipe.:D

I SEE:stirpot::stirpot:

I'd do the 1" bore MC.
1" bore was used on the 67 manual disc option with 4 piston calipers, but those calipers had a little less total piston area than the single piston type you have, so your pedal effort should be lower.
David

I'd do the 1" bore MC.
1" bore was used on the 67 manual disc option with 4 piston calipers, but those calipers had a little less total piston area than the single piston type you have, so your pedal effort should be lower.
David

Thanks David. I hope I'm making the right choice. Like I posted I'm running a 1 1/8" bore master with a 8" dual booster connected to the top hole in the pedal. I just ordered a 67 Corvette Manual 1" bore master. Am I going to have to stand on the pedal to stop this way?

Is there a way to calculate the pressure of a Dual 8" booster with a 1 1/8" master compaired to the 1" with both 6-1 ratio?

How much would this booster put out working correctly?