Brake issues, Need HELP or guidance

[Dmaxed]

The previous owner of the Nova said the brakes are C4's. They are drilled and slotted rotors with decent pads all the way around. My pedal is not the stiffest when press it until it's about 2/3rds of the way down. Then it gets real stiff and the brakes work but not that great. It won't even lock up the wheels. The master cylinder appears to be a stock one from a front disc/rear drum Nova. The booster is now a 7" dual diaphragm. I had it laying around from the S10 so I used it because the stock 11" booster would not clear the master cylinder for the hydraulic clutch. I thought maybe there was air in the lines so I bled the brakes multiple times and played with the Wilwood proportioning valve. Brakes are not my things so I finally got irritated and stumped after a couple days and took it to a local brake shop. They confirmed that I was in fact bleeding the brakes correctly and that there was no air in the lines. Luckily they didn't charge me since they really didn't fix anything after the bled the brakes again. They thought maybe the master cylinder needed replaced or there wasn't the correct amount of vacuum. So I have decided to ask around on here and will call some brake manufacturers and see what their opinion is. I don't have a problem buying a decent master cylinder or even not running a power brakes if someone can convince me that is the way to go. I guess I need a little direction on fixing the problem whether my current setup can work or buying a few new parts. I just want the car to stop really well (don't we all.) If I am going to have to buy some parts I prefer decent ones that wouldn't have to be upgraded later. I prefer to buy the better part the first time instead of wasting money. Ideas?

[IMPALA MAN]

Simply put, the master cylinder must displace enough fluid to push the pistons in the caliper out and clamp the rotors. Another way to put it would be as such: Find out how much distance each caliper piston needs to move in order to clamp the rotors. Add about 1/8" to it for good measure. From there you can calculate the area the fluid needs to displace. Multiply this area by how many pistons are connected to the master cylinder. Now calculate the area of the master cylinder. Usually master cylinders have a 1" stroke, so if you find out the bore, you can calculate the area. If needed Google how to calculate the area of a cylinder. With both areas calculated, you should be able to compare the two and see which one is less. If the master cylinder is less, you have located your problem.

[bovey]

Silly question. Did you change the wheels and or tires? Bigger, heavier wheels will affect your ability to lock up the brakes. Stickier tires for wider tires with more grip will also affect your brake performance.

[Tom Welch]

check the brake pedal pushrod for proper length, this can cause a lot of head scratching when everything else seems to be ok. The rear brakes may be out of adjustment, if they are drums. I would try to verify your parts, then contact Tobin the pro-touring brake go to guy at Kore 3. He will know if the parts are compatible or not. As long as you know what you have.

[Dmaxed]

Impala, I guess I will take a crack at some math over the weekend and see if that sheds any light. Bovey, the tires and wheels are the same ones that were on the vehicle when I bought it. Tom, the pedal rod should be fine. I had to cut the rod to length when I installed the new booster. I do know there was about a 1.5" gap between the rod and the master because the master was a deep pocket. I fixed that already by getting the bullet adapter/spacer from the manufacturer of the booster. The car is front and rear disc that the previous owner said were C4 brakes. I don't know how I can verify them though. The fronts are 2 piston calipers and the rears are single. Guess I may end up calling the brake guy you mentioned and see if he can't school me up.

[Classic Nova & Performance]

Just an FYI: A 7" booster would normally be used on a lighter weight vehicle than your 72 Nova, ie: street rod, etc. They do not give as much power assist as a larger one. I understand that the 11" might not clear some of your components, but would look at a 9" booster. There are several slimline 9" boosters on the market that should give you adequate clearance & more assist.

[Zedzag]

I have Baer track kit brakes, basically c4 with baer logos, and i have the same braking problem you described. My pedal gets stiff around the 2/3rd mark as well and I have the Baer spec's 15/16 master and my factory 1981 11" booster seems to work fine. My engine only pulls 12' of vacuum and I believe that may be problem I'm having. How much vacuum does your engine make?

[Dmaxed]

I haven't made the call yet to Kore3 but I am leaning toward a vacuum/booster issue as well. I have read a few threads about boosters and most of them seem to talk about too little vacuum with cams that are smaller than mine. It has been several years since I bought the cam that is in this motor but I think it is a Comp Cams Magnum hydraulic roller around .600 lift. I can't remember for sure. I have never checked the vacuum so will have to find out how I do. I can't start the car for a few more days now though since I am swapping oil pans after knocking a hole in mine.

[Tom Welch]

Check the engine vacuum with a vacuum gauge, available at parts stores, unplug your booster and connect the gauge to the port on the engine, good vacuum is above 15 inches on the gauge, less than 10-11 inches, will be a problem for a boosted brake system, maybe a manual master cylinder from a c3 corvette would work for you. We have used c3 manual master cylinders on 3 builds, they all work well, it may be of help to you.