Need some brake help/Have some questions.

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 82K5, Aug 25, 2000.

  1. 82K5

    82K5 1/2 ton status

    Feb 17, 2000
    Likes Received:
    kansas city
    I have minimal experience with brakes and thought I would post this and get some help.

    I got a buddy who wants to help me change out his master cylinder for a new one because he lost his brakes last night and figures it must be the master cylinder. His truck is a 1980 GMC Sierra Grande 3/4 ton 4x4 with a 454 motor and a total of 8 inches in lift with 38" TSL's.

    1. If I remember right, he didn't have this problem until the last brake job.

    2. I would think that the first thing to do would be to flush out all the old brake fluid and see if that works.

    3. He is one of those hardheaded fellows, so usually when he makes his mind up, that's it.

    4. I don't have a problem helping him do this, but I hate to see him throw money away on a new master cylinder if it's just the old, crappy fluid. Or would it be a good idea to go ahead and change out the master cylinder anyway.

    5. What are the symptoms of a bad master cylinder?

    6. Is there any thing else that might be the culprit?

    Any ideas and/or help on this subject would be greatly appreciated.

    Thanks in advance,

    Phil Palmer
    Kansas City
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Jul 23, 2000
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    E-town baby!
    Usually a bad master cylinder will have an internal bypass. This will cause the pedal to drop to the floor and greatly reduce the braking ability of the truck.
    I had lost my rear brakes and did'nt have time to fix them and about a week later the master cylinder went and I had NADA! Pretty scary s#*t! I had gone mudding on the banks of a river and all the silt in my rear brakes just wiped everything out. Wheel cylinders, brake shoes, adjusters, E-brake assembly and axle seals.
    It probably is his master cylinder, but if he gets one tell him to get a NEW one not a rebuilt one. A lot of rebuilds have pitting on the machined surfaces and will fail very quickly.
    Definitely replace the fluid, all of it. I used dot 4 fluid because it has a higher boiling point than the dot 3 it originally came with.
    Dot 5 is available and is silicone based so it won't wreck your paint if you spill and has a very high boiling point but, it is expensive and it is usually best if you are replacing all the brake lines too because if it is even slightly contaminated with regular brake fluid it will not have the high boiling point anymore.
    Hope that helps.

  3. jarheadk5

    jarheadk5 1/2 ton status

    Mar 6, 2000
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    If your buddy insists on getting that new master cylinder, make sure to bench-bleed it thoroughly, cause you'll never get the air out of it once it's installed!

    [​IMG] Semper Maintenance!

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