Pedal too firm, before and after many new parts

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?

 

Is this power assist set up or not???

 

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.

 

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!

 

When you were bleeding it, when a bleeder was open would the pedal effortlessly go to the floor?

 

Yes it would.

 

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.

 

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

 

I had a 4-wheel drum car that I converted to power front disc. If you moved the clevis pin down to the lower hole, you shouldn't have to change pedals or anything else.

What is your pedal travel? Before I went power discs, I had a lot of travel and the pedal was about the same height as the clutch pedal. Once converted, the pedal was WAY down towards the floor and the travel was much reduced.

If you have the car sitting and running in park, test how hard the brakes are to push. Shut it off and press the pedal. Is it the same for the first, maybe second and get progressively harder to the point you feel you need to grab the steering wheel to get a good push? If that is true, you are getting some power assist. Why it isn't more, I don't know but I'd suspect master cylinder bore size being too large.

 

Any resolution?

 

I’ve been driving it for a while now and I’ve become accustomed to it… which means sometimes I hit the brakes too hard in our other cars.

I looked into the bore size, and all the listings for a ‘72 Skylark with front power disks show the bore size as 1.125.

Since it’s stopping well I’ve been busy with working on other stuff that needs attention. I guess when I get much of that other stuff out of the way I’ll look into this again. It stops, I can lock up the wheels. I can stop short without doing that.

 

Something is amiss. Ran across this while searching for something else & figured I'd ask. I know someone else having the same issue w/their GS.