Brakes gets no pressure when car in running

Asked by Aug 22, 2013 at 07:42 PM about the 1994 Acura Legend

Question type: Maintenance & Repair

15 Answers

Obviously it's a vacuum leak to the brake booster...probably rotten dry cracked black stuff~ will price out a replacement but confirm that this is what the problem is by A.) waving an unlit propane torch above the hose and see if the idle speed increases B.) a vacuum leak will caused increased Idle speed C.) reduced performance as if the vacuum to the fuel pressure regulator had been removed~

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If the car is idling different than before you noticed your brake issue.......replace your brake booster!

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it SHOULD idle higher than normal with that hose sucking air and stopping the brakes from activating fully~

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That is not always correct. If there is a vacuum leak on the engine side of the booster diaphragm then yes the idle will be affected. If the check valve on the opposite side of the diaphragm is bad then idle will not be affected because the booster will only have a vacuum leak when the brake pedal is applied!

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No need to introduce propane if the engine is idling fine without applying the brakes! If you hear a hissing noise inside the car or the pedal is firm (like when the car is off) then your booster is bad. If the pedal goes to the floor then you have a hydraulic leak in the brake system, this can be confirmed by checking the brake fluid, if its significantly low or empty I'd look for a fluid leak. Common areas include the master cylinder and the rubber hoses at all 4 wheels!

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take 'er easy 805 really was just trying to suggest a way to spot a vacuum leak....perhaps a cardboard tube would be less dangerous~


It's all good.....I would have suggested carb or brake cleaner over propane (easier and more precise) as well. I was just trying to help dabram find his issue with ease, as I am assuming he is not as educated in the automotive world as you and I. As my teacher told me "keep it simple stupid"

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....gotten my ass kicked so many times...Sunday mechanic...ho help...tow ins where the customer is Lording above you expecting to get his car fixed and is willing to wait all day until it's done....rough'll learn quick in this kind of environment~

timing belt...waterpump...cracked distributor cap....coolant return hose missing...flat tire...dead battery....scrapin' brakes....clutch job...SMOG work


I know how it goes.....nothing worse than a customer hovering over you asking every damn question possible, time is money in this industry! I'm happy to help if you have any auto questions

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At least your stayin's dead out here! Turned away 2 engine jobs, one in a 98 G3500 and the other in a Subaru legacy! No money in that.....just a headache!

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was only a Sunday mechanic from '93-'96....service writers often lack in a well adjusted MORAL compass and WILL take the wallet please...thank you~


hit the nail on the head with that one.....most local and smaller shops wont have a dedicated service writer, rather a service writer that also wrenches or everyone contributes to the customer service side of the business. service writers make their money selling services and all too often they have no idea whats going on with the customers car and will sell jobs that do not need to be done! I used to work in an environment like that and i hated it, i was always having to justify his sales. customers would come in complaining that their car runs rough and he would sell them a tune up when the root cause of the problem was a bad O2 or a dirty IAC. Needless to say he got a lot of unhappy customers especially the ones who were smart enough to ask to see their old parts! I believe in preventative maintenance but this guy would try justifying every unnecessary job as preventative maintenance........he had no sympathy or a soul for that matter! Glad i dont work for that a$$h@!e anymore

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Agree. Most service writers today don't have a clue about what they're talking about. Just translate what mechanic says, and often doesn't understand details. "your power steering hose is leaking and needs to be replaced." Really, which hose? Calls back, "the return hose from cooler to resevior. Also,cap seems to,be leaking." Oh, is the rubber gasket under cap filled with fluid, b/c in that case, probably just need to replace $2.50 gasket instead of $200 reservoir. And fluid leaking from deteriorated gasket could run down line and make it appear that line is leaking, when it's just fluid running from worn out gasket. "No, the techs checked that and said return hose has leak and resevior is broken around collar and can't be fixed. Well, OK, but I want all major parts back incl hose, resevior, cap and basket. "No problem. Ready at 5 pm." Go to pick up, and service writer gone for day, can't speak to mechanics (shop policy) and no returned parts -- must have been miscommunication and all parts get commingled so we can't be sure which are yours. OK, this seems to be a conspiracy equal to the Assisi action of the moon rocket and astronauts, and fake shooting of Kennedy bros (or maybe that's backward). Well, I didn't want to tell you, but we have new owner who is devil worshiper and puts spell on cars to make them evil, so,depending on your cars beliefs, well need to get a priest, minister, rabbi, Inman or other religious figure to perform excorcism on your car, because it will try to kill you. "Gee, OK, how much does that cost?" About $5000 but if you give us go ahead in next 15 seconds and pay in full, in advance, we can offer you a big discount. "Really, wow, that's so cool and nice of Lou Cifer Automall. How bigs the discount?" 2%, so with shop fees discount price is just $5400 (5000-100 discount + $500 shop fees), plus 10% courtesy charge for,you to pay with credit card. "Golly, this Lou guys one cool,dude. Let's go ahead right now. Who performs auto excorcism? Oh, Lou does himself. Takes about 5 seconds. And it's guaranteed for life. "Guaranteed for life of car?" No, for rest of your own life. OK. So this allegorical expressionism is not from an actual case. The names have been changed to protect the innocent. But stay away from any new auto dealers or big repair shops called Lucifer's (where prices are sooo low you'll feel all Burt Up.

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