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Technical disc brake swap issue..still got a soft pedal

Discussion in 'The Hokey Ass Message Board' started by Vincentnova, Dec 2, 2018.

  1. Vincentnova
    Joined: Nov 6, 2015
    Posts: 62

    Vincentnova

    yes when i clamp off one side i got a better pedal
     
  2. Check the amount of free play in the rod that goes from the brake pedal to the rear of the master. I've had soft pedals that required the rod be adjusted longer to lessen / eliminate the free play to the master in order to get a better pedal. This is assuming you have an adjustable type rod.
     
  3. Too much free play will result in a lower pedal, increased pedal travel but not a soft pedal.


    Sent from my iPhone using H.A.M.B.
     
  4. Too much free play will result in a lower pedal, increased pedal travel but not a soft pedal.


    Sent from my iPhone using H.A.M.B.
     
  5. Not being there many people confuse soft and low. Both go down too far.
     
    57 Fargo likes this.
  6. Vincentnova
    Joined: Nov 6, 2015
    Posts: 62

    Vincentnova

    i adjusted the rod at the booster . it barely touch the master cylinder.
    i got that little tool that help to adjust it
     
  7. One more thought because I never saw it mentioned, is the system power or manual and do you have the correct depth master for the correct system, shallow hole power, deep hole manual. Also on the rod adjustment, on certain re-manufactured masters ( manual & power ) I've had to depress the piston in order to get a correct pedal. If it's power, on some of the boosters the center plunger is sometimes adjustable also. Good luck !
     
  8. Bleed them off the rotors down near the ground with a pipe , socket handle, something to hold the pistons and or power bleed them, there's still air in them or the Master Cylinder rod is too long or too short so the ports aren't lining up correctly.
     
  9. Garpo
    Joined: Jul 16, 2016
    Posts: 152

    Garpo

    Another rare one to look for is a brake hose 'ballooning'. Have seen this a couple of times, where the hose blows up a balloon about the size of a golf ball. Feels just like air in the system.
    Both times the faulty hose ballooned at the most obscured point, almost impossible to see unless really looking. With foot off the pedal all looks fine.....
    Still have not seen a reason for the camber change.
    Garpo
     
  10. stinger40
    Joined: Nov 10, 2012
    Posts: 23

    stinger40
    ALLIANCE MEMBER

    ^^^^ agreed with Garpo- the hoses could be expanding giving a soft pedal, replace them with good quality hoses.
     
  11. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,284

    Kerrynzl
    Member

    Do you have a soft pedal [spongy] or just too much travel ???
     
    54vicky, 57 Fargo and milwscruffy like this.
  12. Vincentnova
    Joined: Nov 6, 2015
    Posts: 62

    Vincentnova

    Well i replaced the master cylinder with a bigger bore .
    I went with a 1/18 bore

    Now i have a good pedal
    But now when i drive .....i have even less brake...no enough brake to stop the car if i go over 20mph..
     
  13. Vincentnova
    Joined: Nov 6, 2015
    Posts: 62

    Vincentnova

    Sorry master cylinder bore size is 1 1/8
     
  14. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,284

    Kerrynzl
    Member

    What size was the original M/C ?
     
  15. Vincentnova
    Joined: Nov 6, 2015
    Posts: 62

    Vincentnova

    I did a disc brake swap originaly all drums with single pot.
    And the mc that came with kit i believe was a 1 inch bore
     
  16. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,284

    Kerrynzl
    Member

    Try an AC Delco #18M309 Master cylinder [24mm] or slightly over 7/8 bore
    This is a stepped bore M/C from an S10

    The quick uptake part of this cylinder is [31.75mm] 1-1/4" bore which is larger than your 1-1/8" so your initial pedal travel issues will disappear

    The 24mm bore should be small enough to get good brake clamping pressure.

    The problem you're having is a side effect of non-boosted brakes, you have a lot of pedal leverage and hydraulic leverage to get good clamping pressures.
    This equates to a lot of pedal travel when the pistons retract.

    A stepped bore M/C can be used safely with non low-drag callipers

    Your problem here on the HAMB is getting close to 2 months now ! do this and your problems will be over
     
    gimpyshotrods likes this.
  17. Vincentnova
    Joined: Nov 6, 2015
    Posts: 62

    Vincentnova

    yeah 2 months....like i only have to do loooool ...between work and kid...


    will the AC Delco #18M309 fit my proportioning valve or i have to plan on something elses?
     
  18. Kerrynzl
    Joined: Jun 20, 2010
    Posts: 2,284

    Kerrynzl
    Member

    No offence meant about the 2 months comment! Usually with brake problems like you're having means the car is nearing completion and now is having "Teething problems" [2 months is "forever" if you're wanting to drive it]

    Now I just read your first post again.....
    You wrote "now--- engine off I have a mid hard/spongy pedal and when engine is on pedal goes to the floor"
    ARE you running a brake booster? [Engine on/off only affects vacuum boost or hydroboost ]

    If you are running a booster use ACDelco #18M310: this is a 24mm bore with a larger 36mm quick uptake step [for the booster].

    If you're running a remote mounted proportioning valve [beside the M/C or further down the line] then it is only a matter of plumbing, eg: bending the lines and/or changing the flare nuts.
    But usually going from GM to GM is a bolt on affair.
     
  19. Vincentnova
    Joined: Nov 6, 2015
    Posts: 62

    Vincentnova


    no worries i take no offense , 2 months, time fly..
    how many time we also wait for a part (1week) and we it comes its the wrong one ..its part of the game and its also why there is so many projet unfinish for sell online

    your words make sense im going to give a try to this master cylinder
    and will let know how it goes
     
  20. Vincentnova
    Joined: Nov 6, 2015
    Posts: 62

    Vincentnova

     
  21. Vincentnova
    Joined: Nov 6, 2015
    Posts: 62

    Vincentnova

    I got that master cylinder...now with my luck .. .. it wont fit the booster hole ..booster hole smaller.. and i have a small booster because engine is very close...damn it
     
  22. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,326

    sunbeam
    Member

    When you blocked the calipers to check them off the rotors was the block hard to remove or easy? low drag calipers they should have slipped out.
     
  23. Vincentnova
    Joined: Nov 6, 2015
    Posts: 62

    Vincentnova

    it was hard to remove . I took apart the caliper to make sur they were not low drag
     
  24. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,326

    sunbeam
    Member

    I would try opening the bleeder and forcing the caliper piston all the way back an check for any air at the bleeder
     
  25. Vincentnova
    Joined: Nov 6, 2015
    Posts: 62

    Vincentnova

    i bled the shit out of everything so many times
    and using pressure bleed
    calipers out of there braket , bleeder facing up
    banging the caliper as well
     
  26. Garpo
    Joined: Jul 16, 2016
    Posts: 152

    Garpo

    I worked in a specialist brake shop for some years, and problem solving was a regular. Often jobs would come in that had caused considerable grief to the owner. We regularly saw jobs from other workshops..
    With the advantage of test rollers, a hoist, and something like 100 years of combined experience, problems were solved.. Using systematic analysis and sometimes brute force most problems proved to have a simple reason and cure. Always simple when you know and understand what is happening, cause and effect.
    Looking back on this topic, a lot of money has been invested in replacement parts that did not fix the problem.
    With hindsight, I wonder if it may have been cheaper to locate a good brake specialist with several fresh pairs of eyes to sort this.
    Re reading much of this topic I can't help wondering if there is something obvious that has been missed.. Many, including myself have made suggestions based on what is written, but no definitive answer yet.
    I look forward to reading a successful answer to this headache.
    Garpo
     
    Vincentnova likes this.
  27. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,326

    sunbeam
    Member

    Just a thought with the negative camber the bleeder may not be at the high end of the caliper bore.
     
  28. Did you check the pressure again after the MC change that gave you good pedal but no brake force? I think you had 870 before at the front with low/soft pedal, was that right?

    With a power brake system the MC bore should be larger, the pedal travel less because of lower pedal ratio, foot effort less and brake caliper clamp pressure higher when compared to manual brakes. You write and explain that you do not have most of this. Also you mentioned a small booster.
    Tell us more about the booster, your pedal ratio and pressure.

    Some thing isn't working the way it's supposed to, and you are closely describing a power brake system with a booster that isn't working now. Before you were describing a problem closer to low volume.
     
  29. Ron Emerson
    Joined: Feb 1, 2017
    Posts: 133

    Ron Emerson

    I sorry to come in so late but I had a problem once on an ot chevy. Is your master cylinder level with the ground when bleeding, I had to jack up the rear so the master cylinder was level. Air got trapped at the top of the master when not level. Also I don't think you mentioned bleeding the rear brakes after the install of the master cylinder kit. Hope you get it solved.
    Ron.
     
    Vincentnova likes this.
  30. wood remover
    Joined: Dec 23, 2012
    Posts: 852

    wood remover
    Member

    Had a similar problem after a disk brake conversion on a 64 falcon , changed everything on the friggin car looking for the problem couple of masters etc .
    Turned out to be a collasped flex hose at the rear end . Hose looked great but was the only thing not changed , afterall it looked good but it was the culprit
    Good luck
     
    Vincentnova likes this.

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