Brake issues

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by khurrle, Jul 10, 2012.

  1. khurrle

    khurrle New Member

    Hey all, I have an issue I hope some of you can shed some light on...

    A friend of mine has a 96 Chevy K2500 Suburban with the 7.4 in it. Recently the brakes have peen presenting serious issues where the pedal is next to impossible to push and he has to almost stand on the pedal to get it to stop. He already replaced the hydro booster and that seemed to fix it but after a day or two the issue returned.

    Can anyone suggest what to do next?

  2. bazar01

    bazar01 Rockstar 100 Posts

    The truck may have issues with the vacuum assist. Get a vacuum gauge and measure how much vaccum you are getting at the vacuum line from the intake manifold to the brake booster. If you have a vacuum pump, remove the hose from the booster fitting, connect a hose to a vacuum pump and pull a vacuum to the brake booster and step on the brake pedal and see if the pedal effort improves.
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  3. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    All good suggestions; but first, just inspect the vacuum line, it may be plugged.
  4. khurrle

    khurrle New Member

    Thanks for the replies , but his booster is not vacuum operated, it is hydraulic.
  5. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Well, there's your problem, hahaha.

    You could be right; however, it is my understanding, that the 7.4 liter engine is a gas engine displacing 454 cubic inches.

    If it is a gas engine, you have "power" brakes. Power brakes are vacuum over hydraulic. If the pedal is hard to push, most likely the vacuum assist (the power part) is not working.
  6. khurrle

    khurrle New Member

    So it is both hydraulic and vacuum then? Yes he has the 454 gas engine in it, I know that he first replaced the brake hydrobooster which instead of being the big round vacuum guy like mine was a hydraulic mechanism. from there he will need to inspect the vacuum lines below, is that right?
  7. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Ok, it's a poor day when you don't learn something.

    I thought the hydraulic brake booster (operated by hydraulic fluid from the power-steering pump) was used only on diesel engines (no vacuum); and that, all gas engines used a vacuum operated booster (master cylinder).

    I just did a little roaming on the net and it appears, the hydraulic version can also be used on gas engines, my bad, sorry.

    If your friend's truck is using the hydraulic version, the fluid is pressurized by the power steering pump. Perhaps, the pump is not providing the correct pressure.

    Sorry to mis-lead.
    Last edited: Jul 11, 2012
  8. khurrle

    khurrle New Member

    No worries at all, I am not intimately familiar with his truck like I am mine so I was worried I was missing something. Ill let him know and see what he says. is there a way to check the pump to see if its pumping enough pressure?
  9. bazar01

    bazar01 Rockstar 100 Posts

    My bad, for wrong info.

    Power steering pump as stated by RayVoy. could be suspect. Power steering pump supplies brake assist instead of vacuum from regular vacuum assisted booster.
  10. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Sorry, I got called away. I'm sure there is a way to check the pressure, just not sure what it is.
    I would check the fluid level and if it is good, maybe flushing the old fluid and replacing with new might help.

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