Brake Pedal Not Returning & Weak Braking – ’73 Dodge Charger (Black Out Booster + Wilwood MC & Brakes)

[Eddym98]

Hey everyone, I’m having trouble getting the brakes on my 1973 Dodge Charger to work the way they should, and I’m hoping someone here has run into the same issue.

Setup:

• Car: 1973 Dodge Charger, factory power-brake car
• Drivetrain: 512 stroker big block, Tremec T56 swap
• Brake system:
  • 1962–74 Mopar Black Out Series Power Brake Booster Kit (POL)
  • Wilwood master cylinder
  • Wilwood proportioning valve
  • Wilwood 6-piston front brakes
  • Wilwood 4-piston rear brakes
• All new parts, recently installed

The Problem:

• The brake pedal doesn’t always return fully to the top. Sometimes while driving, it sticks partway down and I have to pull it up with my foot.
• I also cannot get the brakes to lock up, even when standing on the pedal. With 6-piston fronts and 4-piston rears, I’d expect way more bite, but stopping power feels weak.
• When the proportioning valve was set more toward “decrease,” the pedal sat closer to the floor. I adjusted it toward “increase,” which improved pedal travel somewhat, but the pedal still occasionally sticks and braking performance hasn’t improved much.

Other Notes:

• Vacuum is connected from the intake manifold (engine has a big cam, so idle vacuum is lower than stock).
• To rule that out, I added an external vacuum pump, but it made no difference.
• The master cylinder was bench-bled before install.
• Lines are fully bled, no fluid leaks.
• I’ve already checked the pushrod length between the booster and master.
• Pedal feel is firm but not confidence-inspiring.

Questions:

1. Since my car is a factory boosted car, is there anything different I should be checking with pedal ratio or linkage geometry when using this Black Out Series kit?
2. Do I still need to add an external pedal return spring?
3. Is it possible my master cylinder bore size is mismatched for the 6-piston/4-piston Wilwood setup?
4. Could there be an issue with the booster itself not providing assist?

Any advice, experiences, or troubleshooting tips would be a huge help. I’m trying to get this car road-ready but the brakes are holding me back.

Thanks in advance!