Ok guys and gals. I know it seems like I always post on here when I need help but where else do you get the best old school knowledge out there. I bought my dream '56 Pontiac not too long ago and have since been trying to get her back on the road. She is running great now so I decided to upgrade the brakes on it. I decided to add a power booster to the firewall and will be doing a disc brake conversion on the front. I bought a 9" gm style brake booster and a C3 style master cylinder to put on. Everything is installed now but seems like I have no brakes. I bench bled the master cylinder till I had just straight fluid going then bled the rest of the system till I had no air. It feels like I have to push super hard on the pedal to even get the brakes to apply. The booster seems to be working alright. I'm just wondering if I don't have enough vacuum or any other problems. I need some advice and or help. I've been racking my brain trying to figure it out.
A few things I can think of. Manifold vacuum,not carby. How much vacuum are you pulling? Manual brake pedal should be about 6:1 ratio from pivot to pedal/pivot to brake rod. Power brake ratio is about 4:1. Also check ECI in Connecticut. Ralph is crusty, but knows his brakes.
Yeah. I thought about vacuum but only can check vacuum off the carb. It's pulling around 15 pounds. I know an ideal would be 18. Should I try using a vacuum chamber or pump? And how do I measure the pedal ratio?
I would think 10# residual Valves Are needed front and rear (4 Wheel Drums)? But not sure what your aftermarket M/C has (some have the residual valves built in) Once you add discs,you might have to switch to 2# Residual for the disc brakes up front (see my coment above) Best thing to do is call the manufacturer/disc kit manufacturer of your master cyl to get expert advise.
From what I've read, I need to go smaller on the master cylinder bore size? The wheel cylinder size should be bigger than the master size?
The stock manual pedal ratio (?) may be too low for a booster, which is normally 3-4:1 for power. All Corvette dual masters are disc/disc and will not have any internal residuals, so 10 lb valves should be installed with drums. When front discs are installed, remove the front axle residual, as they are not needed with the firewall-mounted apply system. If the master and booster are not matched, the booster push rod may have too much clearance with the master cylinder primary piston.
It feels like I have to push super hard on the pedal to even get the brakes to apply. The booster seems to be working alright. I'm just wondering if I don't have enough vacuum or any other problems. I need some advice and or help. I've been racking my brain trying to figure it out. Ok, you can easily measure the available vacuum. You say that the booster SEEMS to be working, but that you need to push on the pedal super hard. Well that just doesn't make any sense, does it? It really shouldn't take much effort on the pedal at all to move enough fluid to take up any hydraulic free play at the wheel cylinders and brake shoe springs in the system. At that point, the shoes should be ready to work. That should remain true in any cir***stance. I'd disconnect the vacuum and see if there's any noticeable difference in pedal effort to rule out a bad booster. With Just a couple measurements and you can get your pedal ratio calculated, couple more measurements and you know the available motion for the pedal pad. Once that proves to be ok, then you can focus on other issues.
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