Register now to get rid of these ads!

Technical Disc brake issue

Discussion in 'The Hokey Ass Message Board' started by aerocolor, Apr 19, 2019.

  1. aerocolor
    Joined: Oct 7, 2009
    Posts: 1,106

    aerocolor
    Member
    from dayton

    Well, I've done complete brake systems for years but I'm dealing with an issue on the '32 while switching out from drum to disc.
    Using a Wilwood four piston race brake setup(new)on the front with stock Ford drum rears.
    Ford style disc/drum master cylinder(new) and discs are plumbed to the large reservoir with an inline 2# residual valve. Pedal is spring loaded up with 1/2" free travel.
    Rears have an adjustable proportioning valve inline.

    The brakes bleed fine and pedal is good but the discs do not release fully and are definitely too tight to drive without overheating .
    I removed the residual valve but no change.
    The lines were blown thru with air pressure to clear them of old fluid before the new parts were bled.
    I can crack the line at the calipers (either side), the master cylinder, any line connection or brake hose and the pressure releases allowing the rotors to freewheel.
    My gut feeling is the master cylinder is not accepting the fluid back into the reservoir.
    Any other ideas I'm overlooking?
     
  2. scrap metal 48
    Joined: Sep 6, 2009
    Posts: 5,504

    scrap metal 48
    Member

    Could your master cylinder push rod be to long or misadjusted and not letting the reservoir pistons release all the way.. Hope I'm explaining that correctly...
     
    Black_Sheep likes this.
  3. 0NE BAD 51 MERC
    Joined: Nov 12, 2010
    Posts: 858

    0NE BAD 51 MERC
    Member

    I assume you changed the front hoses when you did the change over. I have had this acure when the old hoses have become restricted with age. My thoughts are that as you say the master is not bleeding off the calipers when the brakes are released. Maybe see if you bleed down the level of brake fluid in the master for the front brakes so there is room so to speak for more fluid to bleed back. Four piston calipers can displace a lot of fluid as appose to single or dual. Just some thoughts , Brake conversions can be a bitch! Even when you order a complete kit front and rear with what is suppose to be matching components. Scrape metal 48 has a good suggestion too. Good luck Larry
     
  4. aerocolor
    Joined: Oct 7, 2009
    Posts: 1,106

    aerocolor
    Member
    from dayton

    Hey Milo.
    Nope.
    As I explained the pedal/rod has 1/2" freeplay.
    I have made that mistake before. Lol.
    But that's what I'm looking for.
    Ideas that I have missed.
    Bet it's something simple I've overlooked.
    Tired of bleeding brakes.
     
    scrap metal 48 likes this.
    Register now to get rid of these ads!

  5. aerocolor
    Joined: Oct 7, 2009
    Posts: 1,106

    aerocolor
    Member
    from dayton

    Thanks Larry .
    New braided hoses and I've released the fluid in multiple connection points to eliminate collapsed hoses, pinched brake lines and plugged tee fittings.
    The master cylinder reservoir level is down 1/2".
    I'm stumped.
     
    0NE BAD 51 MERC likes this.
  6. Like Scrap Metal said check the push rod travel
     
  7. aerocolor
    Joined: Oct 7, 2009
    Posts: 1,106

    aerocolor
    Member
    from dayton

    Done.
     
  8. KoolKat-57
    Joined: Feb 22, 2010
    Posts: 2,748

    KoolKat-57
    Member
    from Dublin, OH

    Call Wilwood, run it past one of their techs.
    KK
     
  9. aerocolor
    Joined: Oct 7, 2009
    Posts: 1,106

    aerocolor
    Member
    from dayton

    Emailed them today with all the details.
    Normally takes them a while to respond.
     
  10. Pat Thompson
    Joined: Apr 29, 2012
    Posts: 159

    Pat Thompson
    Member

    Apply the brakes. Then open the front bleeder without moving vehicle. If fluid shoots out the problem is either brake hose or master cylinder. How tight are wheel bearings? Might try loosening them one tooth on he nut.
     
    scrap metal 48 likes this.
  11. gene-koning
    Joined: Oct 28, 2016
    Posts: 1,122

    gene-koning
    Member

    Do you have a brake booster installed?
    Most brake boosters have an adjustable rod between the booster and the master that can apply too much pressure on the master, even if there is free play between the pedal and the booster. 1/4 turn in either direction on that adjuster rod between the master and the booster makes a huge difference in the master cylinder performance. Gene
     
    studebaker46, Blues4U and Hnstray like this.
  12. junkman8888
    Joined: Jan 28, 2009
    Posts: 416

    junkman8888
    Member

    Are any of the brake lines near the exhaust manifolds or tailpipes? The guy who originally put together my '63 Chevy "late-modeled" the truck using Square Body pickup parts, unfortunately in the build he tucked the brake proportioning valve inside the driver's side frame rail just below the steering column. After a short drive the heat from the exhaust manifold would cause the brake fluid to expand locking up the front disks, solution was to move the proportioning valve to under the radiator. Best of luck with your project.
     
  13. If you do have a booster; a quick check is to loosen the master to bolts and slip body shims in place. If the calipers release now, you know it is the booster push rod adjustment.
     
    Blues4U likes this.
  14. aerocolor
    Joined: Oct 7, 2009
    Posts: 1,106

    aerocolor
    Member
    from dayton

    Guess I didn't state.
    Manual brakes. The rod is not pressing on the master cylinder at rest position.
    After applying brakes, I can crack the caliper bleeder on either caliper and the brakes free upon both sides until the pedal is depressed again.
     
  15. Is the m/c mounted above or below the calipers and wheel cylinders? Is it possible that the front and rear brake pipes need to be reversed at the m/c? Could there be a residual valve already installed in the m/c where you don't need one?
     
    sunbeam likes this.
  16. raff23089
    Joined: May 15, 2010
    Posts: 63

    raff23089
    Member

    When I did a disc swap on my 50 Plymouth I had the exact problem you speak of. Hours of head scratching and I couldn’t figure it out. I pulled the master cylinder out and realized the C-clip in the back that holds the piston in was bent and holding the piston down a fraction of an inch. I replaced the clip and the problem was instantly fixed.


    Sent from my iPhone using The H.A.M.B. mobile app
     
    Hnstray and chevyfordman like this.
  17. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,796

    David Gersic
    Member
    from DeKalb, IL

    The pedal has 1/2” free play? Or the pushrod does? That’d be a lot of free play between the rod and the m/c piston.



    Sent from my iPad using The H.A.M.B. mobile app
     
    scrap metal 48 likes this.
  18. Fordors
    Joined: Sep 22, 2016
    Posts: 1,743

    Fordors
    Member

    If we assume the typical manual brake pedal ratio of 6:1 that is only .083 p/r to piston clearance. Not terribly excessive but it could be tightened up a touch.
     
    Last edited: Apr 19, 2019
  19. aerocolor
    Joined: Oct 7, 2009
    Posts: 1,106

    aerocolor
    Member
    from dayton

    The pedal freeplay is excessive for elimination/test purposes only.
    The master cylinder is below the calipers hence the initial 2# inline residual valve which has been removed for test purposes also.
    I've plumbed the lines to the correct reservoirs. Large reservoir is the disc brake side.
    Keep the ideas coming. I'm checking them off as we go.
    Thanks guys.
     
  20. it sure sounds like youve proven the problem is with the master cylinder.
    replace repair or rebuild the part would be the next step on the trouble shooting chart.

    should you care to do more investigations, there are residual valves within the master cylinder ports for drum brakes and not beyond the realm of possibility that one of them buggers could be in there where it don't belong. new masters are bad out of the box way to often too. little piece of crap the right shape in the master can cause you troubles too.
     
  21. brigrat
    Joined: Nov 9, 2007
    Posts: 4,650

    brigrat
    ALLIANCE MEMBER
    from Wa.St.

    I have had Wilwoods that came with special washers that you can space out the calipers with.......................................
     
  22. aerocolor
    Joined: Oct 7, 2009
    Posts: 1,106

    aerocolor
    Member
    from dayton

    The master cylinder is new but that's no guarantee it's right.
    I'll replace it and see what happens .
    Will post the results.
     
  23. Andamo
    Joined: Jan 10, 2006
    Posts: 500

    Andamo
    Member

    It almost sounds like there is some sort of check valve in the lines going to the front brakes.
     
  24. robracer1
    Joined: Aug 3, 2015
    Posts: 468

    robracer1
    Member

    this may be a longshot, when I got my 32 it came with Wildwood front disc set up and was having the same problem you are having and found out someone used the wrong rotors that were to thick and finally burned up my caliper and had to buy all new $$$
     
  25. Andamo
    Joined: Jan 10, 2006
    Posts: 500

    Andamo
    Member

     
  26. ffr1222k
    Joined: Nov 5, 2009
    Posts: 1,010

    ffr1222k
    ALLIANCE MEMBER

    If you can release the pressure by loosening the line at the master cylinder it would appear you eliminate everything but the master cylinder.
     
  27. Ralphies54
    Joined: Dec 18, 2009
    Posts: 672

    Ralphies54
    Member

    If after eliminating the RPI you still have pressure that spurts fluid when you open the bleed at the Caliper then more than likely you have a built in check valve in the master outlet. Look in and see, it can be pulled out easily. Ralphie
     
    Black_Sheep and scrap metal 48 like this.
  28. The washers are to center the caliper over the rotor since they are a fixed caliper with pistons on both sides.

    The seal in the caliper is what returns the piston, it’s already been said but the master is holding pressure, the likely cause is the pushrod is adjusted wrong keeping the vent port covered which will cause this. Apparently he has ruled this out so if he cracks the line right at the master and the brakes release then change the master. Or....take it apart and see why it doesn’t work.


    Sent from my iPhone using H.A.M.B.
     
  29. brigrat
    Joined: Nov 9, 2007
    Posts: 4,650

    brigrat
    ALLIANCE MEMBER
    from Wa.St.

    ^^^^^^^^^^We said the same thing except you used a better word! "centered"^^^^^^^^^
    This is assuming the OP has ruled out M/C & everything in between..................
     
  30. Ralphies54
    Joined: Dec 18, 2009
    Posts: 672

    Ralphies54
    Member

    57 fargo may have the answer. If their not floating calipers then the centering is very critical. You may have contact on one side or the other of the rotor.
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2020 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.