A friend of mine ran this one past me -- thought I would post it here: I helped him go through the brakes on a 64 Falcon. He later added a Master Power brake booster and MC to the car. Kept the 4 drums all around. The brakes work fine, except they are a little "grabby." You really have to use a light touch. I checked the front suspension, and it could use a rebuild, and that's affecting the overall feel of the brakes, but otherwise, I'm not sure what's causing it. My first thought was something to do with mating a booster with an MC, but he said he bought them as a unit, so I'm thinking the problem is somewhere else. Maybe a new 10# residual valve? I've done God knows how many R&R brake jobs over the years, but I admit my understanding of general brake theory could use some improvement.
had the same thing happen when i replaced everything on an old drum brake corvette. shoes, cylinders, turned drums, added booster... it was real grabby. after adjusting everything i could think of i learned to adjust myself to the brakes. a couple of hundred miles later, the grabby feel went away. maybe all the new parts need to break-in together. just a thought!
On some Ford PB applications the pushrod is moved to a different location on the pedal. Changes the pedal ratio and the feel of the brakes. On other applications the master cylinder diameter is increased for the same effect. When you simply add a booster to a manual brake system, you could end up with a very touchy system. Overboosted with poor feel. If the stock MC is 1", a larger 1 1/8" master should help.
Is the master drum/drum or disc/drum? I had this with a car that had a disc/drum master with 4 whl drums. The fronts were really touchy at slow speed, would lock them up in parking lot situations. On the highway they seemed OK but I always had to be adjusting the rears manually as the self adjusters weren't activated in reverse because of the way the fronts came on.
yep , same problem here, I changed out a bad brake booster and m/c for a direct replacement for my 65 galaxie four wheel drums and they will lock up easy especially in the mornings, thought about backing off the adjustments?, I will be watching this thread for some ideas.
With drums all the way around I'd go with a bigger diameter master cylinder, that will take some of the overboost effect away.
For what it's worth, a friend added a booster to his brake set up and realized the brakes were staying slightly on. The culprit was the location of the check valve. You might want to check that the check valve, if you have one, is in the proper location in the brake line(s). Good luck.
a the shop i work at we do mustang brake conversions quite a bit. I have to adjust the push rod. does it have a proportion valve? if not try getting one.
The next time I see the car, I'll check, but I believe it had a factory-looking prop valve. My thoughts were that too much pressure was hitting those front breaks, a la an MC setup for a disk/drum combo, instead of the drum/drum combo. I'll have a chance to look at it this weekend and report back.
I put a new master cyclinder (corvette style) and brake booster on my 56 chevy and the brakes were on when I drove it the first time. I separated the m/c and booster and adjusted the adjustment screw/rod? in on the m/c and that solved the problem. Everything works fine now. Maybe that will help.
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