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Hot Rods Soft pedal disk brakes

Discussion in 'The Hokey Ass Message Board' started by vtx1800, Nov 11, 2020.

  1. vtx1800
    Joined: Oct 4, 2009
    Posts: 1,380

    vtx1800
    Member

    Back in August I thought I would upgrade the brakes in my 38 Chevy.
    Here's what I had

    Front--- rotors and calipers
    Rear-- 9 inch Ford drum brakes (70??Cougar)
    Master Cylinder Raybestos MC36440 (spec'd for 76 302 with manual brakes) 15/16 bore
    Master Cylinder is mounted under the floor using the stock pedal assembly to actuate the M/C
    Wilwood residual valves-- 2# in the front line , 10# in the rear line
    Wilwood proportioning valve

    The original setup was OK........but I would have preferred that it stopped a little quicker/better so I upgraded using a Speedway kit
    11 Inch Brake Kit, Ford 5 x 4-1/2 Bolt Pattern
    I bolted it together and couldn't get a hard pedal. I could drive it BUT I didn't have brakes until the pedal was very near the floor. Before you ask....yes the bleeder was on top:)
    I've bleed it numerous times, using the two person technique with limited results. I called Speedway the tech guy thought that maybe I needed a bigger master cylinder so I took a shot at that. Here is the cylinder https://www.speedwaymotors.com/Dual...-W-Internal-Stainless-Steel-Sleeve,50597.html
    Still the same problem.
    Note by this time I had read numerous threads on the HAMB of similar problems trying to find the "fix". One diagnostic suggestion was to terminate the line in various points to see where the issue might be.
    I first plugged the M/C right as it exited the cylinder. Full Pedal,

    Next I disconnected the hard line from one of the flex lines. I had more pedal:)
    I disconnect the other hard line from the flex line and had full pedal.

    Then I unbolted the banjo fitting on the bottom of the caliper using a bolt and two aluminum washers and although it did not form a perfect seal I still had pretty good pedal. I did the same on the other side and still had pretty good pedal even though it leaked a little.

    I contacted Speedway and visited with another tech guy and he didn't have any great suggestions and indicated that they really hadn't had any problems with those calipers, they had sold a lot of them. I asked the tech about the Metric calipers and he said theirs were not the fast takeup style. Note you can't get a feeler gauge between the pads and rotors. They don't retract. Ultimately they sent me a pair of new calipers.

    New Calipers didn't change the issue at all.

    I reinstalled the M/C cylinder with the org Speedway calipers and that brought me back to where I started.

    I have used my home made pressure bleeder but once I get to about 8-9 pounds pressure the top starts to leak so there was limited success....it didn't push the fluid out at all well:(
    Next was another style of pressure bleeder
    Phoenix 2104-B V5 Reverse Brake Bleeder System
    https://www.speedwaymotors.com/Phoenix-2104-B-V5-Reverse-Brake-Bleeder-System,87967.html
    another $50 that didn't work all that well. Very difficult to get a good seal on the hose to the bleeder. To add insult to injury I forgot to put the lid back on the M/C while trying to pressure bleed. It worked well, brake fluid did spray over the seat/steering wheel etc:(

    I had dropped the front of the car down in order get the calipers lower than the M/C thinking maybe that would help. It didn't I also took one caliper off and lowered it more and had the bleeder pointing straight up and lost pedal as we bleed it again.
    EDIT
    Forgot to indicate that I have blocked of the rear brakes with no change in pedal.
    I've installed a new 2# residual valve in the front line.

    I hope I've described accurately all that I have done. Maybe someone looking in from the outside may see something that I've missed.
     
    Last edited: Nov 12, 2020
  2. Are the rear brakes adjusted properly? If they are too loose you will get a low pedal, shouldn’t soft tho. Try clamping off or plugging the rear brake hose to isolate them from the system. At least then you have a firm idea as to which end is causing the problem
     
    Elcohaulic and gimpyshotrods like this.
  3. David Gersic
    Joined: Feb 15, 2015
    Posts: 2,460

    David Gersic
    Member
    from DeKalb, IL

    Pushrod to M/C piston clearance checked? If you lose all of your pedal travel before it starts moving the M/C, you get a low pedal.

    There are dozens of brake bleeding threads here. Everybody has the method that works for them, and I’m no different. Speed bleeder check valve has worked for me, where vacuum, gravity, and reverse have not. Never tried pressure.



    Sent from my iPad using The H.A.M.B. mobile app
     
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  4. fordor41
    Joined: Jul 2, 2008
    Posts: 960

    fordor41
    Member

    I had a low pedal problem with my '41 with Speedway brake kit (GM cals/ MOPAR rotors and 1" Mustang M/C). Speedway said that's common to have pedal 2" or so off the floor. It was scary. I had an adj. rod from the stock pedal to the M/C so I started to lengthen the rod a bit at a time. Watched down thru top of M/C to make sure the piston retracted back past the compensation port and ended up with about 1.5" free travel before firm pedal.
     
    vtx1800 likes this.

  5. IowaTom
    Joined: Jul 23, 2018
    Posts: 28

    IowaTom

    I had a similar problem on my '58 Studebaker with a frame mounted dual system M/C and a disc/drum setup. Bled the lines to death until I realized the issue was a master that flexed about 1/8" while bleeding a line. Not sure where the 'give' was, whether in the frame or the bracket holding the master - or maybe a little of both. I made a not-so-pretty bracing bracket that holds the M/C fast and now I can stop way better. Just a thought. Brake bracket 1.jpg
     
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  6. junkman8888
    Joined: Jan 28, 2009
    Posts: 676

    junkman8888
    Member

    Guys, search "low-drag metric calipers". Might be the answer to your problems.
     
  7. gimpyshotrods
    Joined: May 20, 2009
    Posts: 19,181

    gimpyshotrods
    ALLIANCE MEMBER

    He should set his rear shoe drag, first.
     
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  8. Malibu406
    Joined: Nov 10, 2020
    Posts: 213

    Malibu406
    Member

    Just went through this on my 50 pontiac with power booster under floor. I vacuum bled for hrs but soft pedal. Tried using pressure bleeder but leaked at 5-8 psi. The only way I coul get it to seal was with a ratchet strap up over it and strapped down the the lift. I am sure you could rig up a cross beam if you dont have a lift. I then ran a half quart of fluud after the last bubbles that I saw starting at right rear ending at left front. It worked. I also used dish soap invwater to confirm I finally got it to seal. Good luck
     
    Last edited: Nov 12, 2020
  9. Malibu406
    Joined: Nov 10, 2020
    Posts: 213

    Malibu406
    Member

    Oh and I had one bad residual valve. They are really junkie with just a diaphrambpoppet in them. One of my poppet diaphrams was solid with no slit. I slit it like the others, but I wasnt getting any fluid to that caliper initialky.
     
  10. corncobcoupe
    Joined: May 26, 2001
    Posts: 5,731

    corncobcoupe
    SUPER MODERATOR
    Staff Member

    I've edit this to make it as HAMB friendly as possible.

    If you guys want to discuss anything off topic MII - please do it in Private Conversation - otherwise the whole post could be deleted.

    Or create your own private social group which was set up for things like this and have at it.

    Brakes ARE important but understand if it's off topic - it's off topic and gets closed or deleted.

    Fair enough ?
     
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  11. David Gersic
    Joined: Feb 15, 2015
    Posts: 2,460

    David Gersic
    Member
    from DeKalb, IL

    OP first post says that they are not.



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  12. vtx1800
    Joined: Oct 4, 2009
    Posts: 1,380

    vtx1800
    Member

    Forgot to indicate that I have blocked of the rear brakes with no change in pedal.
    I've installed a new 2# residual valve in the front line.
    Thanks for all the suggestions too.
     
  13. David Gersic
    Joined: Feb 15, 2015
    Posts: 2,460

    David Gersic
    Member
    from DeKalb, IL

    So the changes are in the front, and with the rear line blocked, that isolates the problem to the front.

    Bleeding the front, with your M/C below the floor, I’d think you’d want to raise the calipers as much as possible. Any bubbles would want to go up, not down.

    If you put the old calipers back on, does the system bleed ok and get back to a hard pedal?


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  14. blue 49
    Joined: Dec 24, 2006
    Posts: 1,468

    blue 49
    Member
    from Iowa

    It has been discussed on here before that some "thru-the-frame" fittings trap air. Does your car have them?

    Gary
     
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  15. stanlow69
    Joined: Feb 21, 2010
    Posts: 5,939

    stanlow69
    Member

    Jack the front of the car up as much as possible, then bleed the brakes.
     
    sunbeam likes this.
  16. vtx1800
    Joined: Oct 4, 2009
    Posts: 1,380

    vtx1800
    Member

    nothing that exotic on this car, good thought though! Thanks
     
  17. vtx1800
    Joined: Oct 4, 2009
    Posts: 1,380

    vtx1800
    Member

    @David Gersic @stanlow69 The brakes had somewhat more pedal with the other calipers but it was never where the pedal got hard in the first couple of inches. I did bleed them again with the front jacked up and it may have helped a bit but...I still don't have hard pedal where I'd like it.
    @fordor41 I think I will take a shot at lengthening the push rod on the M/C a bit....all I can do is get the back brakes to lock up all the time:)
     
  18. George
    Joined: Jan 1, 2005
    Posts: 7,480

    George
    Member

    The bleeder valve shouldn't be strait up, creates an air pocket
     
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  19. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,789

    V8 Bob
    ALLIANCE MEMBER

    [QUOTE .....I think I will take a shot at lengthening the push rod on the M/C a bit....all I can do is get the back brakes to lock up all the time:)[/QUOTE]
    The push rod clearance is critical for a good pedal and complete master cylinder stroke-don't guess at it. Adjust the push rod for 1/32"-1/16" max clearance with the pedal fully released by the pedal's own return spring. Now is the time to also check for complete master cylinder stroke before the pedal bottoms out by opening the pri. and sec. circuits. Now you can continue trouble shooting knowing the basics are completed.
     
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  20. David Gersic
    Joined: Feb 15, 2015
    Posts: 2,460

    David Gersic
    Member
    from DeKalb, IL

    [​IMG]

    Maybe. This is what you’re referring to.

    OP’s original brakes were stock calipers mounted on stock hardware, so there *shouldn’t” have been a mounting problem originally.

    The new calipers are same brand (“Ford”), which I’d like to hope are mounted by this kit so that they can be bled. Pictures may help, if we can see some without drawing the ire of the moderators about the OT bits they’re mounted on.

    If the mounting isn’t right, maybe taking the caliper off and bleeding it with a chunk of 2x4 stuck in it will help. Then rotate it to whatever position it needs to be in to get the bubble out.



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  21. David Gersic
    Joined: Feb 15, 2015
    Posts: 2,460

    David Gersic
    Member
    from DeKalb, IL

    Now I’m wondering if you’d be better off with what you had, and getting it working correctly. Then maybe just upgrade to better than stock pads. I like Hawk pads on my 37 and my OT truck.



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  22. WZ JUNK
    Joined: Apr 20, 2001
    Posts: 1,751

    WZ JUNK
    Member
    from Neosho, MO

    This is an excellent illustration of what I think may be the problem I have. My conversion on the Versailles rear end uses GM calipers. I intend to experiment with rotating the calipers and bleeding them in a couple of weeks.
     
    David Gersic likes this.
  23. George
    Joined: Jan 1, 2005
    Posts: 7,480

    George
    Member

    On some cases it's just a matter of having the calipers on the wrong side of the car, try swapping sides & see it it firms up.
     
  24. vtx1800
    Joined: Oct 4, 2009
    Posts: 1,380

    vtx1800
    Member

    Yesterday I pulled the rear drums off and adjusted them tighter than they were. Due to the proximiaty of the spring/lowering block/slapper bar there is no room to use a brake adjusting tool, I have to pull the drum and adjust. No change there:(
    Today I decided to put the one inch bore M/C on, I had bench bleed it before but it had sat and even though it was plugged it leaked a lot of fluid out so I just bench bleed it again, easy to do when it's in a vice. Pulled the 15/16" bore off, and installed the one inch bore M/C again. This time, even before I bleed anything I had WAY more pedal. What changed???? Did I not bleed the M/C properly the first time? The wife helped me bleed the brakes, she remarked that the pedal was a lot better. Although I didn't use the dial indicator to measure the space between the M/C and the push rod, it appeared to be about the same when it was about .025 before.
    Does it stop better than it did before. Not noticeably. Maybe softer pads (wish I'd have thought about that earlier) would make a difference? I think I will just accept that manual disc brakes with out a booster requires a higher pedal effort.
    Thanks for all of the suggestions, I was glad to take the car out and drive it a little today, after two months of messing with it, the frustration level was sorta getting to me.
     
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  25. sunbeam
    Joined: Oct 22, 2010
    Posts: 5,393

    sunbeam
    Member

    Some times on a non stock setup you have to unbolt the caliper stick a block between the pads and turn the bleeder to absolute top to get all the air out.
     
  26. rockable
    Joined: Dec 21, 2009
    Posts: 3,628

    rockable
    ALLIANCE MEMBER

    Are you stroking the MC it's full designed stroke, usually 1". I had the same problem with my 49 Buick and had to modify the pedal ratio to 5:1. It was more than that, which did not allow the MC to use all it's volume and may have trapped some air in it. Anyway, after changing the ratio and bleeding, all my problems went away. Good luck. With brake systems, it seems it's always something.
     
  27. vtx1800
    Joined: Oct 4, 2009
    Posts: 1,380

    vtx1800
    Member

    I've measured it as best I could and it was over an inch, I am using the org brake pedal mechanism (and that is about 5-1 ratio) with a rod going through the org M/C to the dual cylinder so it would get as much stroke as the original M/C.
     
    rockable likes this.
  28. AHotRod
    Joined: Jul 27, 2001
    Posts: 11,595

    AHotRod
    Member

    What is your brake pedal ratio?



     

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