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No brakes!

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Dodonne2, Oct 10, 2019 at 2:35 PM.

  1. Dodonne2

    Dodonne2 Registered User

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    Hi i have lost brakes recently. I push the peddle and it bottoms out and then is harder to push, it does stop the truck but with a lot of pressure. I have been hearing a hissing coming from the driver side engine compartment for a month + so I am assuming I must have a vacuum leak in the system? To add to this, yesterday in traffic down a long downhill I shut the truck off 5 mins or so, for excessive idling and used the brakes pretty heavily down hill with the truck off. After this they seemed fine but then later that night began to bottom out and throw the brake light on the dash. Any ideas. It is a 1986 6.9 n/a with a live-in full size lance camper. It just snowed here in CO so I'd like to get this dialed before I move very far.
     
  2. Kizer

    Kizer Supporting Member Supporting Member

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    First, I'd find out where the "hiss" is coming from and fix it.
    Then I'd check the vacuum pump.
     
  3. Cubey

    Cubey Full Access Member

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    RetiringColt likes this.
  4. chillman88

    chillman88 Supporting Member Supporting Member

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    Given the hiss, I would guess the booster is shot. Troubleshoot first but that's an educated guess.
     
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  5. riphip

    riphip Supporting Member Supporting Member

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    Also, if your truck has Cruise Control under the hood, check the big coffee can on driver's side for leaks on the bottom mount
     
  6. Dodonne2

    Dodonne2 Registered User

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    The air hissing noise is coming from the brake booster assembly. I felt around and couldnt pin point the location. I moved and wiggled all hoses coming to and from the booster assembly and the noise didn't stop. When I shut the truck off it will make the hissing air noise for about 10 seconds till it losses pressure and fades. I am new to any and all brake work within the vacuum system that is. Do I just need to buy a new brake booster assembly? Do they just develop cracks and leaks like this?
     
  7. chillman88

    chillman88 Supporting Member Supporting Member

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    Yes as they age the rubber components dry out.

    I probably would if you can't track down the cause of the hiss.

    Before you do, unplug the hose from the booster and plug it (the hose) with a bolt or something. If the hissing stops completely it must be the booster or the check valve hissing.
     
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  8. Rusgo

    Rusgo Registered User

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    Sounds like the rubber diaphragm inside the booster failed.

    It's likely hissing where the brake pushrod goes into the booster. If it's making noise from inside the cab replace it. It's fairly easy. You can unbolt the master cylinder from the front of the booster and pull the master cylinder foward. You dont lose any fluid when replacing the booster. No bleeding brake. Just mechanical.

    Sent from my SM-G975U using Tapatalk
     
  9. franklin2

    franklin2 Full Access Member

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    I know you are concentrating on the hissing and the brake booster, but you need to also pull the lid on the master cylinder and look at the fluid levels, or look at it if you have a plastic see through reservoir on the master. If the fluid levels look ok, continue on with the booster. If your fluid level is really low in one side, you have other problems.
     
  10. Ayla

    Ayla Registered User

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    You need as new vacuum booster.
     

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