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GMC 6500 Brake Help

Discussion in 'Trucks' started by Cat420, Mar 23, 2010.

  1. Cat420

    Cat420 Senior Member

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    I need some help with the brakes on our truck. It's a 77 GMC 6500 with hydraulic brakes and hydro-boost. Both the master cylinder and booster are shot, but I'm having trouble finding parts. Apparently the hydro-boost stuff wasn't a common option and it looks like the master cylinder is unique to this system.

    Does anyone know a source for the hydro-boost parts or have information like part numbers for converting it to vacuum assist brakes if I can't find parts?
     
  2. Kgmz

    Kgmz Senior Member

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  3. Cat420

    Cat420 Senior Member

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    Maybe I'm missing something, what am I supposed to see:beatsme. That site looks like it has parts that I'll have to custom fit. Our house is being sold in probably a week or so and the truck was part of the deal. I just don't have time to do anything more than swap parts, custom fitting something is not an option right now.

    What I'm looking for is a direct bolt in piece. If the stock hydro-boost stuff is not available or too expensive, I'm curious if the stock vacuum assist parts will bolt into the same spot on the firewall. I can't imagine GM having two different firewall, but don't want to guess. If all I have to do is order the parts and tap the intake for a vacuum line, that would be nice.
     
  4. OneWelder

    OneWelder Senior Member

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    Yellow pages - Truck Parts - these had several different hyd. sys.
    if it is a vacuum system there should be a triangle shape tag on the bolt/clamp that holds diaphragm together - this can be crossed to a replacement. usually school bus
    I do not remember seeing a firewall mounted vacuum booster on that size truck , normally mounted on frame or running board brackets
    you really are not giving enough info for us help much
    Also make sure you really need one on older stuff inside of vacuum hose separates also some get plugged with crud
     
  5. Cat420

    Cat420 Senior Member

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    Thanks, I'll try add some more details. I can get pictures later if it will help.

    1. It is NOT a vacuum system on there now.

    2. Hydro-boost was the name for GM's all hydraulic braking system. It has an electric motor on the booster and also has a line tied in from the power steering pump.

    3. My usual parts place shows vacuum type system available for these type of trucks, but they don't give him any dimensions to verify that it will fit ours. The hydro-boost casting numbers don't cross reference with anything, not even the master cylinder. Obviously we aren't going to order and guess at what will fit.

    I've seen a few guys on here with similar trucks, so I was hoping they had the same system and knew where to get parts or swapped something out after having the same problem as me.
     
  6. Woodboatdave

    Woodboatdave Member

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    I bought one on e-bay 2 months ago for 100 bucks, brand new.
    It was for my gmc c70. I mounts under the driver side step. I can get you the part number Wed. They had many part numbers in the old days but the cross reference narrows it down to the point that one covers many units.
    They are only slightly different for each application, but all do the same thing.
    Worked out o.k. for me, I think I had to bend one brake line.
    Dave
     
  7. Cat420

    Cat420 Senior Member

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    Thanks, that would be great. Maybe a picture as well, if you have time.
     
  8. Cat420

    Cat420 Senior Member

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    Oct 11, 2004
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    Occupation:
    Construction, small engine and machine shop work
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    Pine Bush Ny