Problem with Wilwood Manual Brakes

[theastronaut]

My '66 C10 has squarebody front discs, stock rear drums, stock 6.25:1 manual pedal ratio, and a 1" bore manual master cylinder. It stops very well, can lock up the brakes at speed on dry pavement and pedal feel/travel is great. I used a hold off valve in the front line, and a Wilwood adjustable proportioning valve and 10 psi residual valve in the rear line. It has semi-metalic pads that have been bedded in properly.

We have an Impala in the shop that I just converted to manual disc/drum and it has the same front calipers as my C10. I used a 7/8" on it (I originally thought the brake kit was coming with smaller Metric calipers) and the pedal is soft enough that I'm going to move up to a 15/16" bore. It has a 6:1 pedal ratio, so 1" might make the pedal too firm with not enough line pressure.


Have you bedded in the pads yet? If not they'll grab much harder once they're bedded in.

Are they ceramic pads? Pads are marked with a two letter coefficient of friction code, the first letter is cold stopping friction and the second is hot stopping friction. F/F is pretty good, you wouldn't want lower than E/E or lower with manual brakes.

A major issue I ran into on the Impala- the disc kit came with low-drag calipers that retract the pistons in the caliper farther than normal, so a small bore manual master cylinder couldn't move enough volume to get the piston back out to the pad and build pressure. Look up the difference in the way the piston seal groove is machined and check your calipers to see which version they are. Pre-77/78ish calipers are what you want but some kits are coming with the later 80s/90s low drag calipers that really need a step bore master cylinder to work correctly. The discs kits are coming with huge master cylinders and double chamber boosters to make up the volume and pressure instead of using the proper step bore master cylinder.