1998 International 3800 Power Steering & Brakes Issue

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by ak12.se, Sep 10, 2024.

  1. ak12.se

    ak12.se Bobtail Member

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    Sep 10, 2024
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    I have a 1998 International 3800 School Bus

    The bus has hydraulic brakes with the hydro boost system.

    When I turn the key to the bus the backup pump works as expected and appears to have no issues.

    After the bus turns on I can turn the steering wheel almost fully to the left and right sometimes, other times it doesn't let me go lock to lock or even close without the brake pressure light and backup pump turning on and losing all power steering ability. I also cannot hold the brake and steer at the same time. This appears to happen more when the pumps have warmed up? I can turn the wheel a decent amount and then after a bit of turning and turning it starts doing it. I have attached some videos below. I don't really know how to tell if its the power steering pump or the hydroboost pump or what else it could be. Please give any suggestions. Thanks.

    Videos:
    Inside cab:
    Outside cab (turning as much as it will go): https://youtube.com/shorts/X7jI6Ejuocc
     
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  3. Goodysnap

    Goodysnap Road Train Member

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    How does it drive? Does it only do this while stationary?

    You will likely find that the steering and hydroboost are plumbed in series. If pressing on the brake too hard while stationary the steering will not have enough flow to provide assist. Been ages for me on these systems but that’s what I recall.

    Pressure and flow testing the pump will likely yield normal specs.
     
    Rideandrepair Thanks this.
  4. ak12.se

    ak12.se Bobtail Member

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    Sep 10, 2024
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    It drives and brakes good except for when turning, when turning the brake pressure light comes on and it struggles really bad to turn and often times requires backing up and re approaching the turn. Generally when pulling into a driveway it takes an incredible amount of force to get it to turn in due to the power steering loss. I have not had an issue with the braking at all.
     
  5. Goodysnap

    Goodysnap Road Train Member

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    I’m thinking the brakes get fluid first if you follow the plumbing from the pump to the booster. Then to the gear.

    I would start with having the pump pressure and flow tested. Fluid and filter serviced?

    I remember this being a problem with this setup.
     
    Heavyd and AModelCat Thank this.
  6. ak12.se

    ak12.se Bobtail Member

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    Sep 10, 2024
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    Thank you ill get to checking the pressures after I buy a pressure testing kit. Nothing on the bus has been serviced, the fluid is a bit overfilled and for some reason there is no filter in the reservoir. In the outside video I sent at about 0:39 if you look at the hose coming from the bottom of the reservoir it almost looks like something is taped there? I'm not sure if someone added an inline filter or something as I'm not familiar with these setups but its definitely something I need to check out too. I bought the bus after it sitting for a few years so im just trying to get it driving decently, everything's good except for the turning lol.
     
  7. Goodysnap

    Goodysnap Road Train Member

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    Also since it has been setting. Jack the front axle and make sure you can turn the wheels lock to lock from the wheel end by hand without the engine running. Checking for a frozen king pin or front end / steering part. Grease the king pins and front end up good and make sure the tires are aired up good too.
     
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