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Brake Master cylinder question... with a little update

Discussion in 'The Garage' started by jms, Apr 20, 2006.

  1. jms

    jms 1/2 ton status Author

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    Last edited: Jun 5, 2009
  2. FWP

    FWP CRS

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    Quick question, what's the condition of the front brake flex lines? Stock rubber, or aftermarket? If they're new, I'd swap the master cylinder. As for the other questions, I have no idea.
     
  3. Muddytazz

    Muddytazz 1 ton status

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    When I did mine on my 1/2ton burb, I swapped to a 3/4ton master cylinder (left the booster alone) and have great stopping power. Only thing I'm going to do later on is get a wilwood 4 wheel disc prop valve.
     
  4. txfiremank5

    txfiremank5 1/2 ton status

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    Your booster could be bad. You mentioned the swooshing sound with brake application. Have you tried sitting there with your foot on the brake with the engine running & in gear, to see if tries to stall?

    When mine went it made that noise, pedal got all crappy, but not so much that you knew it was for sure it.. I just knew something wasn't the same. I tried the brake in gear, and it started to stumble after a few moments.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    You can test the booster for leaks pretty easily.

    Start truck, don't touch brakes. Let it idle a few seconds, turn it off. Let it sit awhile (GM says 45 minutes) and then go back and try the pedal. Should have enough left in the booster for two strong applies if it isn't leaking.

    Only time I've been around a failed booster the pedal went rock hard and the truck was no fun trying to stop downhill. :)
     
  6. reptilianman

    reptilianman Registered Member

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    If those calipers have the ratchet type parking brakes the parking brake levers have to be ratcheted thight and released to adj. the piston return other wise would cause a low pedal and high effort.also as far as i know the porportioning valves are different for rear disc.
     
  7. kd7kmp

    kd7kmp Registered Member

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    What 3/4 ton MC did you use? I have heard of swapping MC's to get better brakes. Any guidance would be appreciated. Thanks.

    Kevin
     
  8. R77K10

    R77K10 Banned

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    yep when boosters fail on GM vehicles then the pedal is really next to impossible to depress, and it is REALLY DAMN difficult to stop, without putting both feet on the pedal

    i always check mine by pulling the vacuum hose off after its been sitting a little while

    should have a real good amount of vacuum in it for a long time after its been shut off

    if not then something is bad wrong in it

    if that all checks out then you have a problme in a line, hose, m/c, combo valve assembly, or caliper or something else

    if pedal is spongy or travels farther than it shoudl then check rear shoes distance and for an expanding hose, moisture or air in system somewhere, dont forget air in m/c

    there are quick easy tricks ot bleed the m/c alone, on the vehicle still, real easy

    and is the first thing to do when replacing a m/c especially


    good luck
     
  9. Muddytazz

    Muddytazz 1 ton status

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    When I did mine, I just used a 3/4ton MC off the same year of my rig.
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    That swooshing sound I'm pretty certain is normal, if you listen. I have a feeling it's one of the noises you get used to driving these trucks. :)

    If I was anywhere near my truck I'd start it and see if you can easily hear the noise. Maybe folks that use their trucks daily will try for you. :)
     
  11. txfiremank5

    txfiremank5 1/2 ton status

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    Not starting it in gear, putting it in gear with it running. Hold you foot on the brake and see if the engine starts to idle rough. If so then you have a vac leak, and it's likely coming from the booster if it's a result of doing what I described. It's a least worth checking IMHO.

    I don't agree with that at all. I've had two go out in my GM trucks (my 77, and my 97) in the 22 years I've been driving and that wasn't the case either time. Both times the pedal felt almost normal, but made an 'airy" sound when depressed, and when the pedal was used, and then used again quickly it had a delayed reaction. In other words, if you stopped, and started to go , ... but had to stop again quickly it didn't react well, and was sluggish to respond (in stopping). When sitting at a stop light for a while I could feel the engine start to run rough, due to the lack of vac.

    I would think, though, that it depends on the amount of failure in the booster. For instance in both cases I might have had a small leak, and that's why I got the results I did. Perhaps a large leak etc would have the conditions you described.
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    Yep, exact opposite. When the booster failed, felt like the engine was turned off. New booster, problem solved.

    Plenty of different ways for stuff to fail obviously! :)
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    So for clarification of a setup that works, you've got the '76-78 Caddy calipers, stock 1/2 ton MC, and what is the prop. valve out of?
     

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