The brake booster on my '63 Pontiac would hiss when I applied the brakes and I was slowly losing power assist. I replaced it with a Cardone re-manufactured unit from Rock Auto. Now there is so much power assist that it is annoying to drive. I really need to be light on the pedal. Any thought on what's going on here? Wrong booster? Defective booster? Could I restrict the vacuum line to the booster and decrease the power assist?
Seems like you need to be able to tune the amount of vacuum - wonder if there is a special 'valve' that can be put inline to the vacuum line? BUT - I know little of nothing about these beasts . . . so maybe it is just the wrong size unit or something???
I don't know whether you have a correctly calibrated booster or not, but it is not uncommon to use a restriction port in vacuum applications. It may be treating the symptom, not the cause, but putting a 'plug' in the booster vacuum line with a significantly smaller orifice might be an interesting experiment. Depending on your results, you might 'tune' the orifice size to suit your preference. I believe a restriction won't change the total boost, but would change the rate of application. Ray
I didn't know there was such a thing. Coincidentally I changed out the master cylinder recently. I don't recall there being an option to order a power or non-power cylinder though
I've driven a nice '62 Pontiac and have had a couple of Oldsmobiles from that era. All of them had extremely sensitive brake pedals and took little effort to stop them. I will call it the nature of the beast.
There is no operational difference between a power and non-power master, as long the bores are the same. The differences would be in the push rod bore depths, and external casting provisions for a dust boot on non-power masters. The booster control valve could be defective, as it controls the rate and amount of air entering the booster. Or, it could be you are not used to a properly operating power brake system. Make sure the brakes are in good condition with no sticking or stuck wheel cylinders, free of any grease or oil, and properly adjusted. I would caution against restricting vacuum to the booster. These big drum-braked cars can, at times, need all the help available.
Did the car came with power brake from the factory? If I'm not mistaken a lot of early 60's car had the option power or manual brake and the pedal had two holes to attach the rod accordingly. Check what ratio you have at the moment. You should have a ratio between 4:1 / 5:1 for power brake and 5:1 / 6:1 for manual.
I don't know '63 Pontiacs specifically. Some manufacturers accommodated power brakes by using a larger-bore master cylinder, others used a different-ratio pedal, as Vinnie says.
I doubt that restricting vacuum would do what you want, since the booster "stores" vacuum, and when you first apply the brakes, it will give you full boost. Drum brakes are self energizing, and adding a power booster can make them quite touchy. But if it's hard to drive, it's possible the booster is defective, or possibly the wrong application (wrong core was sold as the one for your car). You could play the return game and see what happens....good luck....
Lots of cars of the era had very touchy power brakes. I doubt a replacement booster would be any different, unless you went with something newer that was valved differently internally.
You can stop them old pontiacs with your big toe. Make sure the rod is in the lower hole on the pedal, maybe drill another lower.
I'm not saying this is your issue, but there is what the other hole looks like. It changes the pedal ratio. Lower for power, higher for manual. Your symptoms kinda match what you'd experience if power brakes were in the top hole.
OK here's what I did...as an experiment I removed the vacuum line from the booster and applied duct tape over the hose barb. I used a 1/16" drill bit to make a hole in the duct tape and reinstalled the vacuum line. I tested the brakes. I had no power assist what-so-ever. I enlarged the hole in the duct tape to 1/8". I tested the brakes again. They felt pretty good. So I took a piece of 7/16 dia. aluminum rod. Cut it 11/2" long and drilled a 7/64" hole from end to end. I inserted this into the vacuum line. The brakes are much better. Still somewhat sensitive. Especially on the initial application. But a lot better. I've driven it several hundred miles this way without issues. I even tried multiple applications of the brakes very quickly to be sure I wouldn't deplete the vacuum. I'm satisfied with it.
Those things were over powered from new. You can check out the pedal leverage etc but if everything checks out good, try pivoting your heel on the floor and applying the brakes gently. With a little practice it becomes second nature.
That's not how vacuum works. What you're doing is marginally reducing the "time" it takes to achieve full vacuum. Once the booster reaches Full vacuum will give you full assist - same as before. The second pump may have reduced assist because it cannot reach full vacuum instantly with your restricter. Exactly like this - "Still somewhat sensitive. Especially on the initial application."
Yep. I know the theory and I didn't really expect any improvement either but regardless it is noticeably less sensitive.
Note the reply from Terry D. on this old thread. http://www.jalopyjournal.com/forum/threads/too-sensitive-brake-question.125678/
A lot of Mastervac style boosters use a reaction pad between the push rod and the booster proper. Looks like a rubber disc about an inch in diameter. Sits inside the 'neck' of the booster. When this drops out the brake becomes very touchy. Often drops into the body of the booster - does not usually do any harm. Need to check a parts list or a competent brake shop to see if this applies to yours. Not difficult to replace - just need to lift the booster away from the firewall and put new one in with a dab of rubber grease to hold it. Can some times do it from the pedal side but need to be a contortionist. A reasonably common fault. Garpo
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