Just put new power brakes on my 55 Mercury Monterey. GM parts. 7” booster and 10psi RPV valves. Drums all the way around. My pedal only moves about 1/2” to stop the car and it’s not feeling like power. Anybody ever had this issue and what’s the fix?
I'm not sure you need RPV's with a highmounted M/cyl and did you check to see if there were valves in the m/cyl port already?
Too much bore and not enough travel. A smaller bore M/C will lower your pedal effort, and increase the pedal travel. GM made a lot of parts. Exactly what was the original application for the M/C you have there? Is it application matched to the booster, and to the brake pedal ratio? Since it’s clearly not OEM, you need to know exactly what’s in there. What bore size on the master? What pedal ratio? What bore on the wheel cylinders? A 7” booster isn’t providing much boost. I have a 9” booster (‘63 Impala) with a 1 1/8” bore master (‘70 Chevelle) and 4.5:1 pedal ratio on a disc/drum system. Pedal is a bit too hard, I’m thinking about going down to a 1” bore master. You could also consider going to a larger booster, if there’s room for it. That would increase the boost applied to the push on the piston. Sent from my iPad using The H.A.M.B. mobile app
That looks like the exact master we put on my 1956 mercury. I am running disc in front though. If there is anything I can do to help let me know. I can look at whatever is on my car (Same car). Only issue I have is the brakes do not feel like power right after starting it up and pulling out of the garage. once I get t the sign at the end of my block all feels great. I am wondering if it may be a vacuum deal on mine. Going to get a vacuum gauge and see what I got.
I purchase one of those from a place in LA which was supplied to me specifically for my F100 pickup project. I found the same brake pedal problem and also noted that it struggled to stop even at slow speeds. Guess where it ended up, in the trash can. What a joke... I feel the issue is too smaller diameter booster is at least one of the problems I had using it. I had disc's up front. I got hold of an early Camaro larger booster and master cylinder, bolted it on and never really looked back. I am sure my pedal ratio is not perfect but it locks up the front wheels if required and the pedal characteristics reflects a power boosted brake system. Pic's attached of the old and the new units on the same vehicle.
That master cylinder does not have residual valves in it. It is an aftermarket duplicate of a Corvette master cylinder, and they had discs on all four corners, the whole time that version of the master cylinder was in production. Residual valves on drums are not just for drain back on an under floor master cylinder. They keep pressure on the seals in the wheel cylinders, keeping them from receding. Modern wheel cylinders don't require that, but he does not have them. Even if he did it would be belt-and-suspenders extra safe. The booster is junk. A full-size OEM one will fix this.
Got it figured out! The master cylinder slug was 3/8” too long. Needed a bit of pedal travel to actuate the booster. Thanks for the input folks!
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