Brakes Grabbing on my '66 390

[Mark66]

I bought a 66 convertible that has sat for a couple of years but is in overall good running condition. The problem is that the front and rear brakes were completely redone within the last 3 years-including the power brake booster and master cylinder. The brakes do work. However, at a certain point they grab and as I press through the spot the braking action returns to normal. Are the power boosters notoriously bad on these babies? What else might the problem be? The booster assembly has less than 3700 miles on it. Thanks!

[Joe Vandatta]

Grabbing is usually caused by some foreign material on the rotor or drum. (grease,brake fluid,etc)I have a 66 and have not had any problems with the booster.
Joe

[CANNEDBAND]

you didn't say wet or dry driving conditions.In my experience some early Fomoco's are more prone to grabbing fromdriving in rain,Bj,Cannedband

[Joe Vandatta]

Pretty much all conditions. Sometimes a leaky rear wheel bearing seal can let rear end fluids get on the linings. I have never heard of the front disk brakes grabbing.
Joe

[Mark66]

Thanks Joe and Canned! Oh and Canned, the car ain't never out in rainy conditions! :)

I'll pull the tires and check things out. One other thing that I forgot to mention: At a stop and with the car idling, when I press the brakes, the RPMs really drop - almost to the motor quitting. When I block off the vacuum line to the brakes and then depress the brakes under the same conditions, the car runs just fine. That's why I was wondering if my problem was with the booster etc. Watcha think?
Thanks Again Shipmates! Mark

[Joe Vandatta]

Sounds like the vacuum line to the booster is bad.
Joe

[CANNEDBAND]

Mark,I think joe's probably got it-it's prob. the line to the booster,unless of course the booster diaphragm has "sprung a leak"in only 3 years service-which is pretty remote.also the front discs will "grab" if the caliper piston seal is so old and weak it won't return the piston back within it's bore,thereby leaving the brake pad too tight against the rotor,creating considerable friction and drag.I never have my bird out in the rain either unless I just get caught in it.Hope you get the "grabbing" stopped.BJ, Cannedband

[t-bird-art]

Notice you are in Pensacola Florida. I am in Daytona Beach Florida. I had a new brake system ( rebuilt: Master , Booster, rear cylinders) all ruined after car sat for 3 years. It was the humidity in Florida. Over 80% humidity on a daily basis. Humidty / moisture gets into everything. Internally the booster has a complicated mechanism with bare metal parts that rust easily. When the mechanism doesn't slip and slide right due to a little rust , it won't work right. I've opened up adozen front calipers. These don't rust and bind up- they are Stainless Steel. Here moisture gets in Master cylinder and gets absorbed in brake fluid. Enough moisture rusts the master cylinder & brake lines ( after 40 years) . Particles of rust end up in the caliper to bind up the piston--causing drag. Moral of this is--these beasts need to be driven and driven often. Worst thing is to leave em sit.