How do you know if the power booster is working.? Car is a 71 GS with a stock 455 ( fresh rebuild) New Power booster. Rebuilt master cylinder. Disk front, drums rear. The brakes do work it's just that I have to push real hard to stop the car. I have a 72 GS convert with same set up (older car) that has awsome brakes. No effort at all to push the pedal to stop the car. Not near like the 71. Any help would be appreciated. Ken
First see how much vacuum you have in this car VS the other. Anything less than 13-14 in.hg. will leave you with a less than stellar pedal. Next thing, a hand operated vacuum pump will show you if it will actually hold any vacuum. If not then first thing is to take the master cylinder loose from the the booster and check the o--ring on the short rod that passes through the the booster and pushes against the piston in the master cylinder. I was recently educated that a lot of suspected booster failures were actually the failure of this o-ring. (Guess how I found out?) You can eyeball the O-ring with one from Napa and only be out about about $.50. Put your pump back on and see if it will hold vacuum now. If that does not do it then you pretty much are looking at a new booster. You can get generic grey steel for about $60 or for a bit more get a get one in gold cad (or whatever they actually are now). Amazon had cheapest price when I was looking a few months ago. Otherwise Jegs has the ones from Right Stuff for about $100 or if you want the Delco stamp then about $150.
This O-ring is quite easy to remove/inspect. Unbolt the master from the booster; there should be enough flexibility in the brake lines to allow moving the master so as to see the O-ring/remove/replace. The original style O-ring is more like a small rubber cup but can be replaced with the later version, which is better described as a disc. I collected a bunch from trans-camaros in the local pick-n-pulls. They have a the disc design but work just fine. Do you hear any hissing when you depress and release the pedal?
To test if the booster is working, step on the brake pedal 3 or 4 times to exhaust any vacuum in the booster. Then place your foot on the brake and press down. At the same time, start the engine. The pedal should drop noticeably, as the engine starts, if the booster is working.
I think what you are describing is more of a dust shield. It keeps crap from getting into the back of the master cylinder piston bore or into the booster itself. The o-ring I'm talking about is actually ON the short rod that passes through the booster. It's got in inner diameter of about 1/4in. A new o-ring and a bit of silicone grease fixed the issue I was having just prior to my engine taking a dump.
Uncle had a similar issue in his 67 with a 455 that he bought a few years back. The break system had only been installed a few years earlier when the car was totally restored. It is a disk front/drum rear setup. It had the right size booster in it with dual master, but the booster was one of those chrome jobs. The car would stop and the pedal felt OK, but the car never stopped very well. We chocked it up to being a crappy setup and it just didn't work to its full potential....no where near it. Uncle hated the chrome booster so he purchased a replacement from Inline Tube with the factory look. WOW, what a difference. That car freakin stops now. It stops like a disc setup should with no fade. So like the others have said, I would check for a vacuum leak and if you can't find one then replace the booster, or if the booster is the leak then obviously replace it anyway.
Talk to the number one booster guru guys on the planet! Booster Dewey or Booster Steve in Portland,Oregon. Power Brake Booster Exchange 503-238-8882 Buick Eric / Oregon :3gears:
I had the same problem after a disc conversion. Turned out the elbow vacuum fitting in the booster was leaking. Replaced it and all good. Cheers, Chris
Well got the Power booster deal figured out. Thanks to : "Larry70GS" for his tip. basically just had to "Burp" the Power booster.. Now I got another problem. When I start the car the Red "Brake" lite stays on. When I unplug the wire from the porporting valve the light goes out. Any ideas what makes the light stay on ? thanks again for all your help.
The light comes on for two reasons, one, there is unequal pressure in the front or back systems and the light comes on, two, the parking brake is on. Sometimes you can make the light go off by pumping the pedal to equalize pressure. Check the master cylinder reservoir and make sure the levels are normal. Check for leaks. Bleed the system to get rid of air.
