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Projects Braking and bore size

Discussion in 'The Hokey Ass Message Board' started by IowaTom, Apr 21, 2020.

  1. IowaTom
    Joined: Jul 23, 2018
    Posts: 11

    IowaTom

    Guys - I've been working on a '54 Kaiser Manhattan sedan and after sending a spindle out to be measured for disc brakes, now have them up front. The rear is a drum 9" Ford.
    My problemo is that I can't get a firm brake after much bench and under-the-car bleeding. (The brake system, not me so much) I'm using an 8" power booster and both the booster and M/C are on the firewall with hanging pedals inside. I believe the M/C I bought on Ebay was billed as a Corvette type - dual, of course - but I don't recall the bore size. Want to say 1" if memory serves. I emailed the guy from the website who made the conversion plates for the disc setup, asking for his advice, but no answer after two emails. (Maybe he's buttoned up the business due to the virus)
    So...I can't find the paperwork that gives me the size of the piston bore in the calipers. Duh on me! My pedal goes virtually to the floor with very little actuation of the brakes. I dare not take this car out on a busy road, now. She's listed as 3,300 pounds without me in it. Can anyone rectummend a bore size or good M/C to try? Oh yeah, I have 2 and 10lb check valves at the M/C for front and rear lines respectively.
    Thanks so much!
     
  2. What calipers are you running?
    Take you about 3 mins to take one off it’s bracket and measure the bore.

    Are the rear brakes adjusted up good where they’re supposed to be ?

    What’s the distance the foot pedal moves?
    How far does the brake rod move for that distance of foot pedal travel?

    Pics usually help too
     
    town sedan likes this.
  3. That damn sneaky fluid strikes again....


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    egads and 31Vicky with a hemi like this.
  4. greybeard360
    Joined: Feb 28, 2008
    Posts: 1,462

    greybeard360
    Member

    You don't need residual valves with the master mounted above the calipers and wheel cylinders. If it is spongy... There is air in the system somewhere or as suggested, rear shoes are having to move too far. Even if the m/c bore is too small, you should get a firm pedal but have excessive travel.

    Try to picture this. Say you have a 1" m/c and a 1" w/c. When the m/c is moved 1", the w/c will move 1".

    If you have a smaller m/c than the w/c, it will move farther to move the w/c but will never move the same distance.... But it will have more pressure behind it. But when the w/c reaches the end of its travel, the m/c can't move any farther.....you cannot compress the fluid.

    So..... Get the air out of the system!
     
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  5. 67drake
    Joined: Aug 8, 2008
    Posts: 64

    67drake
    ALLIANCE MEMBER
    from Avoca WI

    I have to ask- did you bench bleed the master till ALL the bubbles were gone?
    If it was bled on the car was it level while being bled? I’ve seen this trip up too many people.
     
  6. Actually if it’s got drum brakes and the wheel cylinders don’t have cup expanders, then yes you need a residual valve


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  7. David Gersic
    Joined: Feb 15, 2015
    Posts: 2,164

    David Gersic
    Member
    from DeKalb, IL

    This isn’t a kit, you’re building a brake system from parts. Right?

    Need to know exactly what parts you’re using. Research them back to their original application. You can’t, for example, use a 1960s design master cylinder with modern “low drag” calipers.

    Calipers need to be mounted with the bleeder at the top of the cylinder, so you’re not trapping any air behind the piston.

    Bench bleed the master before installing it?

    Is the master / booster / pedal assembly a matched set? If not, you’ll definitely need to measure the clearance of the pushrod to the piston in the master. Too much clearance here, you get no brakes. Too little, the brakes drag or lock up. Should check this anyway, even if it is a matched set.

    Then there’s the actual bleeding process. How are you doing it? Have you done it that way before? I ask, because a friend swears by vacuum bleeding, which I have never had any luck with. I use a check valve in line with the tube on the bleeder and pump the brake pedal. Other guys here use pressure bleeders, or gravity.



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  8. IowaTom
    Joined: Jul 23, 2018
    Posts: 11

    IowaTom

    It's not a matched set. Basically cobbled together, which is probably my main problem. The '54 originally had thru-the-floor pedals to a single system m/c, typical of the day. In my zeal for improving the mechanicals, I have the front disc setup and rear drums with a set of hanging brake & clutch pedals, and room on the firewall for an 8" booster and dual m/c next to my clutch release bearing m/c.
    Again, I bench bled the master - on the car - with a pair of 3/16ths brake lines that bend into the reservoirs.
    Keeping the 10lb residual check valve on the rear brakes, I have now removed the 2lb valve to the front discs and will take the car for a slow spin tomorrow, up & down my street. Yes, I did re-bleed the front calipers and yes, I'm aware bleeders have to be up top, to where the air should migrate.
     
  9. You need to know MC bore size, Caliper size and drum WC bore size before you can make a call.
     
  10. bigdog
    Joined: Oct 30, 2002
    Posts: 533

    bigdog
    Member

    Disconnect the lines at the master cylinder and plug the ports in the master cylinder. How's the pedal? If it's solid, hook up one line and try again. Still good? Try the other line. Narrow the problem down.
     
    scrap metal 48, loudbang and dan c like this.
  11. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,847

    sunbeam
    Member

    Things to look at If you pump the brakes does the pedal feel solid if so your bleed is probally OK. With big pedal travel you have adjustment on rear brakes , pedal ratio is the master piston moving far enough and flex in the caliper brackets.
     
    Lloyd's paint & glass likes this.
  12. Lloyd's paint & glass
    Joined: Nov 16, 2019
    Posts: 2,241

    Lloyd's paint & glass
    ALLIANCE MEMBER

    Just seen the whole caliper expansion thing for the first time recently. Never dreamed that could be possible, but they put a 6" dial caliper over the brake caliper, and when brake pressure was applied, the brake caliper expanded.
     
    loudbang likes this.
  13. What kind of nonsensical trouble shooting advise is that ?:D:p
    You must think you’re smarter than the brake fluid or something.
     
    loudbang and HemiDeuce like this.
  14. Yeah the move with 1000 psi
     
  15. Lloyd's paint & glass
    Joined: Nov 16, 2019
    Posts: 2,241

    Lloyd's paint & glass
    ALLIANCE MEMBER

    Looks to me like much flex would lead to a failure in the center of caliper. After reading all of the brake issues on the hamb, i feel lucky that all my junk stops lol
     
  16. Almost all floating calipers do it.
    The fixed calipers not as much.
     
  17. Do a little math, pressure=force over area.

    1000 psi, and I’ve seen considerably more on gauges hooked to a brake system, is acting on whatever the surface area of the caliper piston has. If you use 2 or 3 square inches then you have 2000 or 3000 lbs of force trying to move that caliper.

    There’s considerable force at work.


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  18. brigrat
    Joined: Nov 9, 2007
    Posts: 5,157

    brigrat
    Member
    from Wa.St.

    "What kind of nonsensical trouble shooting advise is that ?:D:p
    You must think you’re smarter than the brake fluid or something."

    Some ones a little "cranky", smilyface!
     
  19. That’s what she said!
     
  20. bigdog
    Joined: Oct 30, 2002
    Posts: 533

    bigdog
    Member

    Anymore most days I'm not smarter than anything.
     
    31Vicky with a hemi likes this.
  21. A 15/16" or 1" master should be fine. You should be able to stop the car safely with that.

    Again, I see a poor braking thread with a "Corvette style" master in use. I like to use masters that I know the application, my car I use either a Speedway Ford master or one from '72 Mustang.

    I think some of those Corvette masters are either cheap crap or incompatible for a one size fits most application.
     

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