Question about 1995 GMC Suburban

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Brakes hiss when applied, idle raises slightly....

I know its a vacuum prob. but it appears that the vacuum line is connected....???? cant figure it out???

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You have a bad brake power buster take of the tow nuts of the brake master cylinder and the nuts of the power buster on the brake pedal side and you should be able to change the power buster whit out taking the brake lines a part. buy a new power buster before starting, that way you will have and idea what to take a part.

Posted on Jun 24, 2009

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You likely have an internal leak in the booster. Unplug the vacuum line from the booster, plug the rubber line with a bolt or something and see if the eliminates he noise. If it does, then your booster is bad.

Good luck.

Posted on Jun 24, 2009

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1 Answer

92 4runner everything been changed. Brakes, booster, line to booster. Still the same brakes are every hard to push. Can't figure it out any idea. .


Usually theres a plastic valve mounted on the booster thats connected to a vacuum source. Remove it from booster(they usually just pull out) & hose, then suck& blow on one end. Air should pass only one way. If it passes both ways the valve should be replaced. Check to c if hose holds vacuum by placing thumb on hose end to feel for suction (motor running) & to listen for hissing. Replace hose if suction is low &or hisses. Could be a vacuum leak elsewhere in wich case performance would suffer & idle would be eradical.

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What are symptoms for bad brake booster on 1998 Dodge Ram 1500?


Hard brake pedal when applied with the engine running. A quick test for the vacuum assist booster is to shut off engine, pump brake pedal 3 or 4 times and hold on the last pump, start engine and see if pedal drops a bit....if you detect a problem with booster you should check for adequate engine vacuum supply to booster when idling . You can sometime hear a hissing or air leaking when applying brake pedal with engine running if booster is defective

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IT is probably a vacuum leak in the brake booster. With the pedal going to the floor There is either no brake fluid or you will have to bleed the system. Replace the booster and bleed the brakes starting at the longest line first

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Brake Problem


yes but up to a point
the brake pedal should move about 1" to take up the pedal free play and then be applied smoothly as you press further
the harder you press the more solid stopping action you will get
that way you can feel the brakes working so that you can adjust the braking action for stopping
there should be no hissing noise that occurs when the brakes are being applied
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---------This will help.Thanks.

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Air leaking thru brake rod in firewall raising idle of motor when brakes applied vey hard pedal


You may have a vacuum leak in the master cylinder or vacuum reservoir. This would cause the idle to increase and also the brake pedal to be hard hence there is not enough vacuum assist for the power brakes. First check the large vacuum line leading to the brake reservoir for leaks but more than likely the master cylinder will need replaced. With today's ABS brake systems it takes special equipment to work on the brakes so it will need to be repaired by a qualified shop.

Feb 07, 2011 | 1987 Chevrolet S-10 Pickup

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Surge in idle when brakes applied or after driving..


block off vacuum hose to brake booster and see if idle returns to normal if it does you need new brake booster has hole in diaphram internally some times slight hissing noise is evident in cab when pressing brake pedal to section where engine surges or idles high. also check for fuel leaks from hoses if you can smell fuel in engine bay while running and engine warm some leaks only leak while running and hot

Jun 14, 2009 | 1992 Nissan 300ZX

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ENGINE TURN OFF WHENEVER I APPLY THE BRAKES


You must have a serious vacuum leak under your hood somewhere. Use a stethoscope, or a lenght of vacuum line held to your ear, and wiggle all vacuum lines around while listening for a hissing.

Jun 04, 2009 | 1985 Mercedes-Benz 190

1 Answer

1989 dodge Ramcharger stalls


Hi Monkeypaint!
I assume you have power brakes and I gather that it idles properly at times, but dies when the brakes are applied. This sound like a leaking power brake assist vacuum line or diaphram. You can verify this by locating the big vacuum hose connecting the intake manifold to the assist diaphram. This will be about an inch in diameter connected to the round item behind the brake master cylinder next to the firewall.
  1. Disconnect the line at the intake manifold end, and plug the vacuum port on the manifold with a tapered rubber stopper or cap.
  2. Being aware that you now do NOT have power assist to the brakes (requiring CONSIDERABLY more pedal pressure to stop!!!), see if the problem goes away. If it does, you have narrowed it down to the assist diaphram or the hose. If it still persists, it is an engine tuning/control issue, not related to brakes.
  3. Do determine whether it is the vacuum hose or the cannister, remove the previously installed cap/plug, reinstall the hose to the intake manifold, disconnect it from the diaphram and plug/cap the hose at that end. Repeat step three... if the problem returns, the hose is leaking and should be replaced... If the problem still goes away, the Power Brake Assist Diaphram Cannister is leaking excessively and should be replaced.
  • ***ALSO*** Any other vacuum lines leaking can lower the manifold vacuum to a threshold level where the load of power brake assist actuation crosses the line for adequate vacuum to idle*** So check all vacuum lines underhood, looking for a pronounced hissing at vacuum leaks. A manifold vacuum gauge is a relatively inexpensive diagnostic tool that could also be useful.
Well, hope this helps, and good luck! Don't forget to rate this answer!
Thanks!
-WB

Jun 15, 2008 | 1989 Dodge Ramcharger

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