1971 Plymouth 'Cuda 440-6 power brakes with stock front disc, rear drum.

Both of my front brakes seem to be locking up. The car drives and stops fine.   I can't feel the brakes drag and the car does not pull to one side or the other when I apply the brakes or when cruising. I noticed a lot of brake dust on the front wheels so I jacked the front end of my car up and both front wheels where really hard to spin by hand, like really hard.   Both rear wheels are fine. The parts that are new or freshly overhauled: power booster, master cylinder, both calipers, discs and pads. At that point, I replaced the master cylinder with a different overhauled one.   Same problem. If I let the car set for a while, the pressure lets off until I drive the car again. Any ideas?


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take off the line from the M/C port next to the firewall and stick a drill bit deep down into the brass cone seat & you'll feel the springy RPV if it has one. Thread a screw into the cone and lever it out then toss the RPV then replace the brass cone seat. If it has no RPV check that the calipers ain't hanging up on the grooves (sliders) & if good there replace the calipers. Some calipers dont retract the piston enough for minimal drag. EDIT I'm assuming the line next to the firewall goes to the front discs

I suppose that you mean Residual Pressure Valve by the RPV reference?

Id crack the front line open to see if there is pressure. If so check to see if the front wheels are hard to turn still.

or crack 1 caliper at a time. if they are holding pressure its possible that the rubber lines are bad.

Also check to make sure your brake pedal is going back all the way, mine was sticking a little and was not coming all the way back. Had the same symptoms.

Having this exact same issue on a cuda build I finished.

Tracked to down to the new valves on the inner fender are not releasing quick enough.

If you hit the brakes and the 2 ft wheels will be maybe 5 seconds before they can spin, rears are fine.

Once released they will spin just fine. I just don't like the delay on release.(neither does the cars owner)

You might want to consider that you've neglected to adjust the piston rod end of the booster that resides in the bore of the master cylinder, it may be applying pressure creating some residual drag on the front calipers, and possibly overstroking the master upon full braking application....your looking for at least .060-.080 clearance between the piston/rod end and the end of the master's bore

Missed that it was power brakes. I bet Dayclona nailed it, not enough clearance