stevns71monte Posted January 12, 2011 Share Posted January 12, 2011 my brakes are acting up, i hear a hissing sound like a vaccum hose is disconnected but i checked all of them and they are good. but the pedal is weird i barely tap on it and my brakes lock up but it only does it on the first few minutes of driving after about five minutes of driving he pedal is fine until a red light then it hisses again and gets soft? i triple checked all the vaccum hoses that go into the brake booster what else should i check? Quote Link to comment Share on other sites More sharing options...
Mike 57 Posted January 12, 2011 Share Posted January 12, 2011 Does the sound seem to be coming from the booster assembly? That might be a good thing to check Quote Link to comment Share on other sites More sharing options...
stevns71monte Posted January 12, 2011 Author Share Posted January 12, 2011 ill start it and see but from inside is sounds like its coming from inside the dash Quote Link to comment Share on other sites More sharing options...
stevns71monte Posted January 12, 2011 Author Share Posted January 12, 2011 yes its coming from the assembly, and my brake pedal is really soft Quote Link to comment Share on other sites More sharing options...
stangeba Posted January 12, 2011 Share Posted January 12, 2011 Not sure but it sounds like the booster diaphragm may be leaking or the check valve isn't "checking" like it should. The check valve is the easier thing to check and or replace. It's a one way valve that keeps vacuum in the booster for one or two applications after the engine shuts off. Bruce Quote Link to comment Share on other sites More sharing options...
bigtankjones Posted January 12, 2011 Share Posted January 12, 2011 Yeah it does sound like the diaphragm is bad if you can hear it from under your dash. Quote Link to comment Share on other sites More sharing options...
stevns71monte Posted January 12, 2011 Author Share Posted January 12, 2011 how would i check or where is said diaphragm? Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted January 12, 2011 Share Posted January 12, 2011 First thing to do is with the car off pump the break pedal a few times it should get hard and high then with your foot still on the breke with some pressure on it start the car the pedal should fade down a bit if it does the booster is working if it is shut the car off then pull the little plastic valve out of the booster blow into it from both ends one way it should let you blow through it the other way it wont if thats good then put it back and see if you can find where the hissing sound is coming from. a length of vacuum hose may be helpfull there one end by your ear and the other searching around the booster. try that Quote Link to comment Share on other sites More sharing options...
zmanabba Posted January 12, 2011 Share Posted January 12, 2011 The diaphram we are all refering to is in the metal brake booster can behind the brake master cylinder. Easiest way to do is to start the car and pinch the hose off that goes in to the brake booster with a pair of pliers or vice-grips. The sound should go away. A lot of times it is the diaphram that needs replaced. You could try to rebuild it yourself (don't know about parts availability and it takes A LOT of torque to untwist the halves) or you could find a reasonable used one to use while you have a specialist rebuild the original. I don't know of any rehaps someone else can chime in. At any rate make sure your system is SAFE. Don't want to lose you or another Monte. Unless you promise to run over a Mime...............lol David Quote Link to comment Share on other sites More sharing options...
Mike 57 Posted January 12, 2011 Share Posted January 12, 2011 I hate to say this but just in case: If you try to listen for a vacuum leak with a piece of hose put it CLOSE to your ear not in it! Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted January 12, 2011 Share Posted January 12, 2011 I hate to say this but just in case: If you try to listen for a vacuum leak with a piece of hose put it CLOSE to your ear not in it! I didnt say in I said by Quote Link to comment Share on other sites More sharing options...
stevns71monte Posted January 12, 2011 Author Share Posted January 12, 2011 i started the car and kinda layed down and put my head close to the brake pedal. it was really loud there. when i push on the brakes it stops, and it seems like when i push on the brake when its just idling the pedal stays down and my brake lights are constantly on. i checked the brake fluid level and its full. Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted January 12, 2011 Share Posted January 12, 2011 Originally Posted By: Mike 57 I hate to say this but just in case: If you try to listen for a vacuum leak with a piece of hose put it CLOSE to your ear not in it! I didnt say in I said by BTW that works for exhaust leaks too Quote Link to comment Share on other sites More sharing options...
stevns71monte Posted January 13, 2011 Author Share Posted January 13, 2011 replaced master no luck. replaced check valve nothing all thats left is the booster itself, replacing that this weekend hopefully Quote Link to comment Share on other sites More sharing options...
stevns71monte Posted January 13, 2011 Author Share Posted January 13, 2011 anyone? Quote Link to comment Share on other sites More sharing options...
MGD72Monte Posted January 13, 2011 Share Posted January 13, 2011 As this sounds like a vacuum issue, the brake booster would have been my third pick after checking all the linkages and confirming no leaks in your vacuum lines and then replacing the check valve. If it were mine I would probably have disconnected the vacuum from the booster to see what changes occur in the symptoms. I'm not sure why you chose to go with the master cylinder, but it was probably old so it's not a loss but there is no vacuum related to it. Good luck with the booster, hope it works out for you. Quote Link to comment Share on other sites More sharing options...
Mo's70MCs Posted January 13, 2011 Share Posted January 13, 2011 anyone? You need to determine whether it's VAC or HYD problem.. in the vacuum assist or the master cyl releasing its pressure. I'm assuming you bench bled the master cylinder & bled the brake system? Sometimes leaks in the master cylinder can allow brake fluid to be siphoned into the booster and play havoc on the diaphragm.. at times enough to be sucked into the intake manifold, signs of wetness on the inside of the hose are good tattle-tell signs of a leaking master. Also wetness under the master where it bolts to the booster, I've seen it drip (brake fld) into the inside of the car, right in the area of the brake pedal.. onto the rug. To check the vacuum booster, pump the brake pedal with the engine off until you've bled off all the vacuum from the unit. Then hold the pedal down and start the engine. You should feel the pedal depress slightly as engine vacuum enters the booster and pulls on the diaphragm. No change? Then check the vacuum hose connection and engine vacuum. If okay, the problem is in the booster and the booster needs to be replaced. Quote Link to comment Share on other sites More sharing options...
black07ss Posted January 13, 2011 Share Posted January 13, 2011 When you say they lock up do you feel it is the front, rear or both. It could be two seperate issues. If you feel it is the rear you may be having some issues with your parking brake linkage. If it is not released all the way they could cause it to act that way. You need to take a look and see if the shoes are touching the bar that is inbetween them. I also feel it is the booster making your hissing sound. Quote Link to comment Share on other sites More sharing options...
LuckyKenny Posted January 13, 2011 Share Posted January 13, 2011 When you say they lock up do you feel it is the front, rear or both. It could be two seperate issues. If you feel it is the rear you may be having some issues with your parking brake linkage. If it is not released all the way they could cause it to act that way. You need to take a look and see if the shoes are touching the bar that is inbetween them. I also feel it is the booster making your hissing sound. He said last night on the phone that it was the front. He also said he's going to replace the booster this weekend. Quote Link to comment Share on other sites More sharing options...
stevns71monte Posted January 13, 2011 Author Share Posted January 13, 2011 Originally Posted By: stevns71monte anyone? You need to determine whether it's VAC or HYD problem.. in the vacuum assist or the master cyl releasing its pressure. I'm assuming you bench bled the master cylinder & bled the brake system? Sometimes leaks in the master cylinder can allow brake fluid to be siphoned into the booster and play havoc on the diaphragm.. at times enough to be sucked into the intake manifold, signs of wetness on the inside of the hose are good tattle-tell signs of a leaking master. Also wetness under the master where it bolts to the booster, I've seen it drip (brake fld) into the inside of the car, right in the area of the brake pedal.. onto the rug. To check the vacuum booster, pump the brake pedal with the engine off until you've bled off all the vacuum from the unit. Then hold the pedal down and start the engine. You should feel the pedal depress slightly as engine vacuum enters the booster and pulls on the diaphragm. No change? Then check the vacuum hose connection and engine vacuum. If okay, the problem is in the booster and the booster needs to be replaced. yes i bench bled the master and the whole brake system, the first master i bought from o rielly's did that i returned it and got one from autozone and it doesnt leak. yeah after i replaced the master and bled the brakes the pedal got nice like how it was supposed to be i turned the car on and it depressed slightly like its supposed to do except the pedal slways stays down now. i rev the engine and you can see the pedal move up and get all its vaccum but still making the hissing noise and acting really weird. is there anything special i have to do to replace the booster? Quote Link to comment Share on other sites More sharing options...
Mo's70MCs Posted January 14, 2011 Share Posted January 14, 2011 Not really! Although some re-builders would not ever sell the unit by itself. Most will sell the rebuild as a whole assy, I think it has something to do with liability. I guess it's easy to mismatch the master and the booster. I've replaced mine with the newer units available, and have gotten different results in brake performance..for instance a smaller diameter M/Cyl bore, has given me a stiffer pedal and quicker stopping. Where as the designed M/cyl gave an ok feeling pedal and a larger reservoir for the front disc. The length of the rods is another thing to be careful for, if I remember correctly there is two different lengths. Unbolt from the brake pedal, undo from the firewall.. and presto,, you can even leave the master attached to the hyd lines. Quote Link to comment Share on other sites More sharing options...
Mikstudie Posted January 14, 2011 Share Posted January 14, 2011 As Rod said dont remove lines from master. Underdash you will need a extension and 1/2 deep swivel socket. This job is fairly easy. Quote Link to comment Share on other sites More sharing options...
bigtankjones Posted January 14, 2011 Share Posted January 14, 2011 Did you find anything out yet? Just curious. Quote Link to comment Share on other sites More sharing options...
stevns71monte Posted January 14, 2011 Author Share Posted January 14, 2011 no i checked all my vaccum again just in case and everything checked out im just going to replace the booster, any tips? Quote Link to comment Share on other sites More sharing options...
Mo's70MCs Posted January 14, 2011 Share Posted January 14, 2011 Steven,, Vacuum testing the engine,,will give you the answer. If your have a leak in the booster,,it'll show in a manifold vacuum test. A must for any "BYM". Quote Link to comment Share on other sites More sharing options...
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