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JB7 brake system question

Discussion in 'The Garage' started by mechted, Sep 5, 2005.

  1. mechted

    mechted 1 ton status Premium Member

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    does anyone know which port on the master cylinder is front and which is rear on the JB7 brake system? Is it the large line (0.25", rear supply) in the front or rear port as the cylinder sits in the vehicle?

    The lines seem to changed from the way they were... and inspection of other trucks around here has yielded more questions than answers. (1 each way...)

    this was a 85 C10 with plastic reserviors and is now a 85 C20... the lines seem to have switched front to rear from the previous cylinder? can that be right?
     
  2. 55Willy

    55Willy 3/4 ton status

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    just swap the lines to the right size ports, my brothers 79 jimmy had to be done that way when he added a 3/4 ton cylinder off the same year suburban.
     
  3. beater_k20

    beater_k20 Banned

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    front portion of the MC is for the rear brakes, rear portion is for the front brakes. has been that way on EVERY GM truck i've ever worked on.
     
  4. 55Willy

    55Willy 3/4 ton status

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    there is a difference between 1/2T's and 3/4T's.
     
  5. rumbly truck

    rumbly truck 1/2 ton status

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    The front resevoir on master cylinders is usually the the biggest one , the rear being the small one. Disc brakes require a greater fluid volume for activation. Look at the sizes of the pistons in a caliper. Then look at size of a wheel cylinder. Drums get a lot of their power from the self energizing effect.
     
  6. 55Willy

    55Willy 3/4 ton status

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    i know this. i manage an auto parts store I have catalogs full of this stuff and about 60 of em on the shelf. I'v also done 3 4wheel disc conversions, and 4 half to 3/4 ton swaps. I'v also done manual to power swaps.
     
  7. mechted

    mechted 1 ton status Premium Member

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    thanks, thats what I wanted to hear
     
  8. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    Yepp, I took the one off my Blazer and replaced it with a 3/4 ton model. The front res. was smaller and for the rear brakes, and the rear res. was larger and for the front brakes.
     

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