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if i press the brakes and my idle changes does this mean vacum leak???

Discussion in 'The Garage' started by down4thakrown, Jul 30, 2005.

  1. down4thakrown

    down4thakrown 1/2 ton status Premium Member GMOTM Winner

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    on my DD when i press the brake pedel the idle changes. does this mean i got a vacuum leak? possibly just a wore out hose?
     
  2. original balzer

    original balzer 1/2 ton status

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    a tiny change is normal but that usualy isnt very noticable. id say it its real noticeable its probably a vaccume leak. you can use carb cleaner to check for leaks lightly spray arond hoses and fittings while its running and listen to the engine. if the engine speed changes inspect the hose or fitting you just sprayed

    balzer
     
  3. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    That's normal (as long as it's a small change in idle that last a few seconds.) It's just a change in manifold vacuum as you suck the servo diaphram in. If it's a big change in idle speed and is high all the time you have your foot on the brake I reckon it'll be your servo leaking.
     
  4. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    WOW... did we type that at the same time?? SPOOKEY!!! lol :D
     
  5. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Talk about being "on the same page"...:eek1: :D

    Rene
     
  6. diesel4me

    diesel4me 1 ton status Premium Member

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    listen closely...

    All the GM trucks I had with bad power brake boosters not only had little or no power assist,the engine would stall or idle rough as long as you applied pressure to the brake pedal,and you could hear a hissing noise under the dash near the steering colum..

    There is a bolt hole in the master cylinder casting on the bottom rear--on 67-72 trucks they used that hole to mount the brake proportioning valve,but later trucks still have the hole there--my trucks that had vacuum booster failure(ruptured diaphram) you could hear the vacuum "leaking"(sucking??) in that hole--I found it by spraying carb cleaner in the bolt hole! :eek1: --

    There is a smaller hole that goes to the rear of the master cylinder casting from that bolt hole that you cant see when the master cylinder is bolted to the booster..not sure why its there,but I guess it serves as a "vent" for the vacuum when the diaphram fails,or maybe its to let air in so the diaphram can return to its normal position when the brakes are not applied?...at any rate,when the diaphram fails,you will have a vacuum "leak" at that bolt hole in most cases.. :crazy:
     
  7. Stoner42

    Stoner42 Registered Member

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    Vacuum leak would be in the brake booster- nowhere else with that condition.If it was elsewhere engine would always idle high.
     
  8. az-k5

    az-k5 1/2 ton status

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    I am guessing you have a booster vacume leak, or a booster on its way out. It happened to me about 3 months ago.
     
  9. blownout

    blownout Registered Member

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    no way

    no its fine the truck is old .
     

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