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  1. #1

    Default Hydroboost abs k2500 4x4 issues. Need help!

    OK here is the story. I'll try to make it short. I bought this 94 K2500 suburban. It has a 350 and 4x4 with abs and hydroboost brake system. As of now the brakes and power steering are not working. This all started with a cracked pressure line. I replaced the line which ran into the steering column. The issue continued so I topped off the power steering pump and took the cap off to bleed the lines. I simple locked the wheel back and fourth a few times. Still nothing! I then changed the Ps pump and still nothing changed. When locking the whole back and fourth the steering pump starts foaming fluid. The brakes have a whinning sound when depressed and the sound is the same when the steering wheel is turned. Is the hydroboost unit bad or do the brakes just need to be bled as well? I find it too ironic to have the Hydro unit fail at the same time a pressure line cracks. Is there a proper procedure for bleeding these hydroboost units. I was under the assumption they are self bleeding systems. Any help is much appreciated.

    Thank you
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  2. #2


    welcome to gmtc. Maybe I can guide you down the right path with your issue. I am not familiar with the hydroboost system in the 1994 but, I am familiar with the system in the 2005. Maybe they are similar enough that my info will help you out. When I replaced my hydro booster the included instructions claimed that the hydrobooster is self bleeding. Here is the procedure for testing that came with my new hydroboost unit:
    1. With engine off, apply and release brake pedal 5 to 10 applications to deplete
    accumulator reserve pressure. With foot slightly pressing brake pedal, start engine.
    Pedal should drop and then push back against your foot.
    2. With engine running, turn steering wheel until lightly against steering stop. After
    5 seconds return wheels to the straight ahead position and turn engine off. Apply and
    release brake pedal. There should be at least one power assisted brake application.
    Start engine and allow accumulator to recharge before moving vehicle

    As far as your power steering fluid foaming, it is because the level got too low and the fluid aerated. Which is not a good thing. The fluid has no lubricating properties when in the foam state. I am wondering if your issue is that you just need to get all of the air out of your power steering system. When I changed my ps pump it came with bleeding instructions that I had never seen before. If said to jack up the front so the tires are off the ground. Fill the pump reservoir with fluid and then, without starting the truck turn the wheel from lock to lock 30 times. recheck your fluid level. If all is good start the truck and let it run with the cap off for a few minutes. I had never seen instructions like this, I called a few mechanic friends and asked them about it. They had never done it either. So, I tried it and it worked great. the fluid never foamed. My mechanic friends are now using this method all the time to bleed the systems of air.

    1995 Silverado 4x4
    6" BDS Suspension Lift-3" Body Lift-Add A Leaf in rear -Trailmaster SSV Shocks-Duel Steering Stabilizer Kit -AirAid Cold air intake-
    4.56 Gears with Detroit Auburn Locker-Pro-Comp Traction Bars with duel shocks-Aluminum Skid Plate Kit-38.5" x 16.5" Mickey Thompson Baja Claws-Constant Dropping fuel gauge

    2005 Yukon XL Jet Power Programmer, Bilstein Shocks, Bilstein rear springs, Helwig Anti-sway bars, EGR Window Visors, EGR Hood Shield, Denali Headlights, Headlight harness upgrade, GE NightHawk Bulbs, White Night Rear lighting system, Russell Braided SS brake lines, PowerStop Brake pads, PowerStop cross drilled and Slotted Rotors,
    2002 Silverado ext cab 2wd (Sold)
    2003 Yukon XL (Totaled)

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  4. #3


    Your info was very helpful. Thank you very much. I will try this Saturday when I get a chance to get back on the truck. I guess I'll bleed the brakes just because then try the method you suggest and hope it works or at least makes the situation better.

    Thanks again pikey!

  5. #4
    Jr. Engineer Jamm3r's Avatar
    Join Date
    Dec 2012
    Minneapolis area


    Hi Joe

    Quote Originally Posted by Gmtruckguy84 View Post
    I guess I'll bleed the brakes just because
    First of all this is a power steering problem, not a brake problem. I guess there's no harm in bleeding the brakes but it's not going to fix anything either.

    Getting the power steering lines bled should not be a big deal although it will take longer on a hydraboost unit.

    If there is foam in the reservoir then wait until it subsides before continuing. Be sure there is fluid in the reservoir at all times.

    Bleed the powerboost unit first by operating the brake pedal a bunch of times with the engine running. Then bleed the steering gear by turning the wheel lock to lock. Have someone watch the fluid level or get out and check it often during this process.
    Minneapolis area - 1997 K2500 regular cab long bed + 8.5' Western Unimount plow + modified transmission + 2nd battery + modified camper charge circuit + 1971 Cayo camper -and- 2004 4x4 Suburban 2500 8.1 + Maxbrake controller + 2nd battery + modified trailer charge circuit + Reese receiver, pulls 30' Airstream trailer

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