I put wilwood 4 wheel disc brakes on my 68 charger still using factory pedal. The brakes are for 15 inch wheels I can get the part number if needed. The master cylinder bore is 1 1/8, I have an 8inch dual booster. There is no way I can get the brakes to lock up the pedal is like standing on a brick, the car will stop but is not right. I'm thinking I need to go to a smaller bore, but what size options are 7/8, 15/16 or 1inch. Has anyone here dealt with this?

Doctor Diff is the man to go to on this

Is your vacuum booster getting vacuum and actually working? "Standing on a brick" is a pretty common way to describe a boosted system with no assist.


I have manual Wilwood discs and started with a 7/8" bore and moved up to a 15/16" to reduce the stroke some. There's no reason for you to need a smaller bore, in my opinion. I have no problem locking the car down with manual 4-wheel Wilwoods and a 15/16" bore.

I'd suggest verifying the booster operation, perhaps checking the caliper pressures you are getting and also thinking back on if you bed the brakes in properly.

Ok did some checking and with engine off pressed down on brake pedal and held then started car and pedal might have moved 1/4 inch. Hooked up an external vacuum pump that pulls 27 inches and had the same result but with the engine off I could hear a shhh sound very time I pressed the brake. Also measured and the pedal is only moving 1.5 inches from rest.

Some of the "big" Wilwood calipers have small bores. The area of the pistons is what matters. I got caught on that, once, years ago. Figured big calipers, big MC. Measure the bores, do the math and it makes sense.

Went from 1 1/8 to 7/8. Went from using 2 feet to stop to going through the windshield if you want. Pedal travel was a touch long for my taste but not a deal breaker. Owner liked it so... Don't remember the car having power brakes. Worked fine without it.

Power brakes make a difference.