harder than normal brake pedal

[crewchief]

I have 69 coronet 500. It has been converted to wilwood 4 wheel disc brakes, I'm using stock power brake booster which is new with wilwood master cylinder. The pedal his harder than normal but not as bad if the booster was bad. The motor is nothing radical; 318 with mild cam and runs approx. 13-14 inches of vacum @ idle. Wilwood says it's not enough. Anybody have any experience using electronic vacum pump,if so which one???

[DartGT66]

Propably adding more vacuum will not help. I believe that's the nature of disc brakes, they don't "self boost". They also needs usually more fluid displacement than drums and therefore a bigger master cylinder piston diameter; when the area gets bigger it needs more power to create pressure.

[cudabob496]

I hooked up an extra vacuum cannister to my power brakes, and that helped.
Wonder if the plunger diameter is correct on the Wilwood master cylinder?

[John Kunkel]

"Hard pedal" can mean several things. Rigid calipers will have a harder pedal than floating calipers.

How does the car stop? If you're experiencing a hard pedal with reduced stopping power the pushrod in the booster might be extended too far.

[crewchief]

The pedal is hard with minimal brake pedal travel. Seems to have reduced stopping unless you really push HARD on the pedal but is driveable.The m/c bore size is correct for power brakes per wilwood. If I recall there is an adjustment on the rod between the m/c & booster. I know I had to adjust that rod because the rod hole in the m/c was deeper then the original so I measured and adjusted up the difference??? They are rigid calipers because they are 4 piston type.

[cudabob496]

Possible crimped or plugged brake line, which makes pedal hard due to inability to move brake fluid.

Or is proportioning valve completely shut?

[Ray Bell]

Or the position of the pushrod from the pedal is wrong?

[DartGT66]

I have been told that steel braided teflon brakelines also tend to make the pedalfeel harder than rubber hoses. I also have fours wheel discs, Wilwood HD's in front and Ford motorsports in the rear, and the pedal feel & needed pedal force is also pretty hard. Don't have a booster though, but the brakes are "worse" than with the factory front discs. 60 lbs lighter though...

[Ray Bell]

Braided lines reduce sponginess, they shouldn't make the brakes harder to operate efficiently.

[DartGT66]

That's what I tried to say by making the pedal harder, not the required force.

[cudabob496]

Originally Posted by DartGT66

I have been told that steel braided teflon brakelines also tend to make the pedalfeel harder than rubber hoses. I also have fours wheel discs, Wilwood HD's in front and Ford motorsports in the rear, and the pedal feel & needed pedal force is also pretty hard. Don't have a booster though, but the brakes are "worse" than with the factory front discs. 60 lbs lighter though...

60 pounds unsprung weight is big!
I also shed 10 pounds per front tire by going to some
eco-type tires that runs higher pressure, and have a low rolling
resistance! Some tires are very heavy, which slows you down!

[crewchief]

Been thinking and playin' around with this problem. Today I drove it and sped
up in low gear let it decel which would increase vacum and brakes felt BETTER.

[Ray Bell]

You would seem to have a basic problem relating to cylinder and caliper bore sizes/relationship...

Can you try a bigger caliper piston size?