andros Posted May 10, 2010 Report Share Posted May 10, 2010 So I'm driving home as I usually do and something started to hiss/whine when I hit the brakes. I stopped for some gas and checked the brake fluid levels, fine. I peeked behind the wheels to see if there was a drum or brake line leakage, nothing. I could figure out what was causing the noise but I determined that the noise was from the master cylinder / booster area. Another thing I noticed was that when at a stop, the whining was putting some sort of strain on my engine. My hypothesis was that it was something that is causing drag on the accessory belt, doubting that it is an engine issue. What are your thoughts on this? I was a bit upset but not resenting the fact that I have a faulty brake system. If we do conclude that it is the brake sys them thats a good enough reason to finally do a disk brake conversion. I wanted to get the community's input on this issue just in case this is a commonly occurring thing. Quote Link to comment
MicroMachinery Posted May 10, 2010 Report Share Posted May 10, 2010 If you suspect the brake booster, unhook the vacuum booster line that goes to the intake manifold and plug it. Run the engine, and if the hissing goes away, you know it's a leak in the booster diaphragm. The strain that you feel it put on your engine could be the leaky diaphragm acting as a vacuum leak. Un-metered air entering your engine will cause it to run roughly, as any other vacuum leak would. Quote Link to comment
Creepy Cruiser Posted May 10, 2010 Report Share Posted May 10, 2010 Yep, sound like the booster has gone bad, and is creating a vacuum leak that is making the motor fun funny too. What kind of car/truck? Quote Link to comment
datzenmike Posted May 10, 2010 Report Share Posted May 10, 2010 Had the same thing yesterday. I replaced the master/booster and took for a drive. The motor shook and idled bad and there was a funny fluttering sound sort of like a sax. I lifter the hood an immediately saw that I forgot to plug in the booster hose. The engine was sucking air through the one way valve. That was making the noise and the bad idle. They seldom go bad, so check the big hose to the booster and also the much smaller capped pipe at the one way valve that is there for the automatic. If the hose is split or loose it will hiss and cause a bad idle. Quote Link to comment
andros Posted May 10, 2010 Author Report Share Posted May 10, 2010 Yep, sound like the booster has gone bad, and is creating a vacuum leak that is making the motor fun funny too. What kind of car/truck? 620. Had the same thing yesterday. I replaced the master/booster and took for a drive. The motor shook and idled bad and there was a funny fluttering sound sort of like a sax. I lifter the hood an immediately saw that I forgot to plug in the booster hose. The engine was sucking air through the one way valve. That was making the noise and the bad idle. They seldom go bad, so check the big hose to the booster and also the much smaller capped pipe at the one way valve that is there for the automatic. If the hose is split or loose it will hiss and cause a bad idle. Sounds like you experienced the same thing I did. I checked all of the lines and they seem to be in the right places and in working condition. Would there be a leak if the booster had gone bad? Either way, I would need to replace both the master and the booster for a disk brake conversion? Quote Link to comment
datzenmike Posted May 10, 2010 Report Share Posted May 10, 2010 Pull the hose off the booster and plug the end. If it idles better and the hiss is gone then the leak must be inside the booster. If you go to disc then just get a '78 or '79 13/16" 620 master and booster. Quote Link to comment
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