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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. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,383

    landseaandair
    Member
    from phoenix

    By the way, brake lines are no where near as close to the header as the pics seem to show. Rear line is closest at about 1" and will have a heat shield eventually.
     
  2. It's a 1 inch bore and the rear bowl (closest to mounting flange) is for the front brakes.
     
  3. Vincentnova
    Joined: Nov 6, 2015
    Posts: 64

    Vincentnova

    and with this master cylinder , how did you do for the brake line between the MC and the proportioning valve ?
     
  4. I'm not really sure what you're asking me, but I used 3/16 line for front and rear. I used a residual valve in both front and rear (master mounted under the floor) and the proportioning valve also mounted in the rear between the master and the prop valve.
     
  5. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,383

    landseaandair
    Member
    from phoenix

    Think I solved my issue and it had nothing to do with air, bleeding or faulty parts. After hitting a wall and swapping masters twice, combo valve, lines, rpv's, calipers, etc. with no difference whatsoever I threw a third master with a 1 1/8" bore on there and pedal is exactly as it should be. Haven't tried any high speed stops, still need to get the car legal, but went around the neighborhood and seems fine. Other two cars may have had an early third gen disc/drum master like an Auto Zone M1494 that looks very similar to a Vette style with a 1 1/8" bore.

    [​IMG]

    Don't see how with the volume those big single piston early GM calipers (now Advance Auto 18-4040, 18-4039) soak up anybody could get by with anything smaller. The car stopped ok but pedal was excessive and way past center, with the mechanical advantage at that point I was able to flex the caliper ears and put it all the way down. Wonder how many people that recommend the 1" haven't actually tried it and have power with the bigger master themselves, different calipers or pedal geometry? I've got a 6.4:1 pedal 6" off the floor and just under an inch of piston travel, all original with intact return spring and bumper, pushrod adjusted properly.

    Hope this somehow helps the O.P. Have messaged back and forth with him and know how annoying it can be unnecessarily changing parts and losing paint just to be right where you started.
     
  6. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,383

    landseaandair
    Member
    from phoenix

    Just wan't to add I don't actually have the master pictured on the car now it's got a Vette style (Advance MCA89160) since it was new and in stock near me.
     
  7. Vincentnova
    Joined: Nov 6, 2015
    Posts: 64

    Vincentnova

    Happy father day to everyone

    Well i got the master cylinder suggested
    The Raybestos MC-39177
    Bench bleed it
    Bled system again
    And still have same problem
    Feel like calipers dont grab enough...
    Quick stop impossible
    If i drive at 10mph and stomp on pedal car only slow down..

    With engine off I still dont get a rock hard pedal . pedal still feel kind squishy
    im at 3:1 with the pedal ratio .
    i went 3:1 just to try to get a better feel in pedal.
    Going 4:1 to 3:1 didnt change at all how the brake feel when i do a test drive...

    To this point im pretty sure that is not the master cylinder
     

    Attached Files:

  8. Some fucking days at some times you’ll need stuff like this.
     
  9. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,957

    David Gersic
    Member
    from DeKalb, IL

    Have you checked the pushrod to m/c plunger clearance? If there’s too much play there, you get no brakes.



    Sent from my iPad using The H.A.M.B. mobile app
     
    milwscruffy likes this.
  10. Kan Kustom
    Joined: Jul 20, 2009
    Posts: 2,315

    Kan Kustom
    Member

  11. Vincentnova
    Joined: Nov 6, 2015
    Posts: 64

    Vincentnova

    do you mean the booster pushrod to the MC ?
    yes i did .
    i have that little tool that help you to adjust it

    but talking about that, i did a test...kind of test you do when you are desperate ahah
    i unscrew the push rod a little ,just to make it longer than it should be
    and brake are a little better????
    wheel wont lock if i slammed the pedal , still cant get an emergency stop .
    but definitly the brake grab better

    and never mentioned , while driving the car i can pump the pedal as much as i want ,it wont build more pressure or better stoping
     
    Last edited: Jun 18, 2019
    David Gersic likes this.
  12. It seems you have covered all bases here, yet you don't have brakes that work the way they should. If it was my car I would probably start from scratch checking things like brake pedal linkage, push rod adjustments, caliper slides and caliper mounts. All those things that should be right and at this point are being taken for granted that they are all right. Also, a second set of eyes looking things over might be a good idea. You may be looking past what another person may see as a problem. Good luck.
     
  13. Yes,,, ^^^

    “I’ve checked everything, three times, and it’s all good,,,, but brakes don’t work“
    Well then your brakes WORK because everything checked good
    “But they don’t work”
    Then check again,,
    “I’ve checked it 4 times now and it’s all good”
    If it’s all good then the brakes work
    “But they don’t work”

    It’s Obviously obvious the brakes don’t work and that means there’s a problem and previous checks scratched off as good are false.
     
    F-ONE likes this.
  14. distributorguy
    Joined: Feb 15, 2013
    Posts: 28

    distributorguy
    Member
    from MN

    If the master cylinder plunger is partially pushed in all the time, you won't get the full amount of fluid displacement. Shorten your pushrod until there is 1/16" of slack in it and try that. If you're running a power booster, make sure it isn't holding the master cylinder piston depressed. I just battled with this for 3 weeks on a '56 handyman wagon and I was shocked that shortening the pushrod inside the booster was the solution.
     
    pitman likes this.
  15. Funny 35 years ago the only way I got brakes on my Model A was to indeed lengthen the adjustable brake rod to actually depress the plunger about a 1/16 of an inch. Went from soft pedal to screaming to a stop great pedal and brakes. Drove it 4 years and 30,000 miles after that and it's still the same over in Austria now. You can go too far and the brakes will build pressure and calipers will lock up on there own without touching the pedal. With the quality of parts now, I would jack up the drivers front tire, adjust the brake rod longer while someone spins the tire and keep adjusting until you can feel resistance on the tire. Back it off a 1/2 to 3/4 turn and see what you have for pedal. At this point, what have you got to lose ? For the record mine were manual brakes.
     
    Last edited: Jun 19, 2019
    Vincentnova likes this.
  16. Vincentnova
    Joined: Nov 6, 2015
    Posts: 64

    Vincentnova



    Yeah i think that is going to be my next step.....
     
    milwscruffy likes this.
  17. jcwilliamsj
    Joined: Feb 17, 2018
    Posts: 11

    jcwilliamsj

    so what's the latest? did you figure it out?
     
  18. diceman
    Joined: Apr 10, 2007
    Posts: 27

    diceman
    Member

    img017.jpg 20190829_112305_001.jpg View attachment 4415050 View attachment 4415050 Did you get your problem resolved? If not I may have a solution for you. I have installed 2 of these systems and have had the same problem with both. Check to see if the caliper anchor pins are perpendicular (90 degrees) to the rotor.
    After I jumped through all the bleeding hoops several times and not once getting any additional air out of the system I started looking for another problem. What I found was the mounting bracket is not square with the rotor. This causes the caliper and therefore the pads to sit cockeyed on the rotor. This means the piston has to travel farther to square itself up before it can clamp the rotor which causes long pedal travel. When you release the pedal the caliper will spring back to its crooked position. When I corrected this problem on mine the brakes started working great. Another hint that this might be the problem is to look at the wear pattern on the rotor. Mine had little or no wear on the inner 1/3 of the rotor on one side and just the opposite on the other.
     
    pitman and RICH B like this.
  19. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,383

    landseaandair
    Member
    from phoenix

    Pretty sure at some point in his process of elimination he put solid blocks in the calipers which would negate any deflection of the caliper brackets.
     
  20. Binkman
    Joined: Nov 4, 2017
    Posts: 198

    Binkman

    I bought a '34 Ford a while back. The car sat for many years and the brakes barely worked. I decided to gut the car and do a lot of the car over and update it. When I got to the the brakes I noticed that the front brakes were the only ones working and they often froze up. I looked at the master cylinder and it was corroded and only partially working. The rear wheel cylinders were completely seized up.
    I replaced everything and went with one of the Corvette style 1 inch master cylinders I had in stock.
    The car did not stop as wall as I thought it should. I went back to basics and installed OEM wheel cylinders and a 13/16" master. The car now stops with very little pedal effort.
    I suggest you get the parts that are matched and you should be good to go.
     
  21. ‘34 ford didn’t have OEM wheel cylinders.
     
  22. 54vicky
    Joined: Dec 13, 2011
    Posts: 1,118

    54vicky
    Member

    probably the rare option called future brakes:D
     
  23. Vincentnova
    Joined: Nov 6, 2015
    Posts: 64

    Vincentnova


    no....
    last test was to connect the front line and only the front line to the master cylinder without proportioning valve...
    stil the same
     
  24. Vincentnova
    Joined: Nov 6, 2015
    Posts: 64

    Vincentnova


    thanks a lot for this idee . i have not think about these...
    for now i just cheked the passenger side.
    and the pins are dead straight ( believe me I wished they were not.....)
     
  25. jcwilliamsj
    Joined: Feb 17, 2018
    Posts: 11

    jcwilliamsj

    do you think it could be the proportioning valve pushed off center during the bleeding process?
     
  26. I wouldn't use a stock proportioning valve on a HAMB friendly car without good reason. Look at a CPP part number 63090 proportioning/distribution block. They go for like $70 on eBay and work quite well, I have one in my car that uses a GM front disc swap.
     
  27. Vincentnova
    Joined: Nov 6, 2015
    Posts: 64

    Vincentnova


    I eliminate the proportioning valave . right now I only have the the front brake line connected to the master cylinder
    the port for the rear line is plugged
    (master cylinder with both port plugged the pedal is rock hard even with engine on or off )
     
  28. Did you spend 50 on the testing kit with pressure gauges yet??

    Think of being lost in the woods ,,,, that kit is your compass and It stops the guessing and gets you pointed in the right direction. Sorry there’s no air lift rescue chopper in there - you have to walk.
     
    alanp561 likes this.
  29. It’s way more fun to take wild ass guesses and throw parts at it...diagnose something, pfffft....crazy talk.


    Sent from my iPhone using H.A.M.B.
     
    bobss396 and 31Vicky with a hemi like this.

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