My 1972 Skylark originally had drums. But when I found a donor car for everything else it needed I swapped over the disc brakes, master, booster, proportioning valve. Always had too firm a pedal, had to press really hard way in advance to stop. The rotors were way too shiny so I figure they were glazed and so were the pads. In October I replaced: Master Cylinder (with the same AC Delco with the bigger front reservoir than the rear) Brake booster Drivers side hard Front brake line from proportioning valve to frame New steel braided lines from frame Wilwood two-piston calipers Slotted and drilled rotors Redid rear brakes with all hardware, new shoes, drums, cylinders The pedal was still overly firm but after bedding in the brakes the car will stop, quickly if need be. I made sure the pedal Clevis pin is lubed, it’s in the correct hole (I think, now I wonder if I changed the actual pedal/pedal arm… are they the same between drum and disc cars?) The rod from pedal to booster was set correctly and isn’t at an awkward angle. Maybe it just needs a new proportioning valve? Also maybe the front brake hard line has too many bends in it, at too small a radius and that’s restricting flow? But that would probably make one front brake work better than the other and induce a pull or one wheel locking up? I’m used to it and feel confident it’ll stop, but my wife and son aren’t and neither is a friend I let drive it that’s also a car guy. Compared to all our other cars past and present the pedal is probably twice as firm. That’s why when I drive one of the other cars the first time I brake I end up stopping short. Any ideas?
Where do you have the vacuum line to the booster hooked up? Is there anything plumbed into that line?
Big cam? What's vacuum reading? Master piston size? Drums have 7/8" or 1". Disc's have 1-1/8". Better pedal with smaller bore masters. Maybe re-bleed system? My pwr drums used to throw you threw the windshield. Disc's not so grabby. My vacuum is only 5-1/2". Storage canister helps. Not like new cars & trucks. Turns you into a defensive driver.
Bone stock 350 18-21 vacuum per the gauge I have and a handheld one. Booster vacuum feed is plumbed directly to the engine via its own dedicated port on the rear of the manifold. Master cylinder is whatever several parts suppliers list as the correct one for disc/drums. System bled and re-bled several times.
Does your booster hold vac. Start car let it run a little shut it off for 5 mins pull check valve out of boostet.....if it holds it will such air Check vac level after the check valve....just because I have it at the intake doesn't mean u have it at the booster
Did you only use the top bleeder screw to bleed front brakes . My wilwood calipers have a top and bottom screw, use only the top one.
To check the booster, press the brake pedal 3-4 times with the engine OFF to exhaust any vacuum in the booster. Then hold pressure on the brake pedal while starting the engine. If the booster is good, you will feel the pedal drop as the engine starts.
18-20" is plenty for a booster to work properly. Have you replaced the hose or checked it over? If it's rock hard toss it. It could also be collapsing when its running or kinked A stock system won't require anything out of the ordinary to work properly.
Used only the top screws on the caliper since bubbles rise. Booster holds vacuum. So did the one I took out. I replaced it because the old master leaked into it. I’ll see if I can get some new hose. I don’t remember when it was changed last. thanks for all the brainstorming. You folks are great!
Many years ago I had a 1973 Chevy pickup with the same issue. The previous owner had rebuilt the brakes with new reman MC, calipers, and booster. I got the truck cheap because of the hard brake pedal. After replacing nearly everything but the booster, I went to a junk yard and bought a booster and MC from a good truck that was driven in. I swapped in the used booster/MC for the new reman parts. End of problem. I then reinstalled the reman MC and all was still good. The reman booster was bad. IDK why. All checked out but I never took it apart to find out more.
If I'm reading this correctly, the problem arose when all the parts were swapped over from the donor disc brake car? Prior to that the car had a soft pedal? I'd probsbly agree that the booster you installed is suspect
Prior to the swap the car had a blown motor and was likely headed to the scrap yard. I never drove it but I rescued it. I drove the donor car and don’t recall having this issue. The booster I installed in October is remanufactured, but the pedal was hard before it was changed. It’s not as hard to stop as it was before all this brake work but still firmer than it ought to be. Could a vacuum hose that feels firm on the outside be collapsing on the inside? Maybe the booster (and the one it replaced) were not getting enough vacuum, even if the engine produces it. Someone suggested that I think. I guess I could buy a foot of vacuum hose and try.
It's. Not hard to pull the check valve and adapter your gauge to the end to verify you are getting the proper amount actually where you need it..........don't assume, know. Its what I was saying earlier6
