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Thread: Brake help

  1. #1

    Default Brake help

    I picked up this old girl 3 months ago at a yard sale, her husband had died Vietnam Vet she wanted $500.00 I gave her $3,000.
    She didn't know what she had. Bike last ran in 84. What I need is front brake help, Hurst Airheart calipers on a a 8'' disk. forks are
    36' another 18'' to the 7/8 handlebar. I put a Willwood banana on the back it is on or off. to harsh. It was a showbike everthing was chromed. It is rough but runs. I need help master cylinder to calipers plus lines. 1/8 npt to 3/16. Thanks. (Durfee front end).
    Attached Thumbnails Attached Thumbnails 20200809_160032.jpg   20200809_160039.jpg  

  2. #2
    Senior Member

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    Looks like you have the 150 calipers, that have a 1/8" inlet, since it is a girder, you can run solid lines up to the top, join them at a tee, and a single 3/8' braided flex to you m/c.

    Click image for larger version. 

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    Hurst Airheart, is now just Airheart, who quit making a part of their lineup with new ownership of Tolomatic last January;

    see their parts sheets here for reference;

    Can still get the H-A 150 calipers and o-ring rebuild kits for them here:

    The 150 calipers are to be in a certain position, I believed it is at the top, with some degree of variation, not in the horizontal position...will try to find that info again.
    EDIT; its 3:00 or 9:00 position for the 150 calipers; just had to follow the Speedway Motors caliper link...:

    "The Airheart 150x1 Series Disc Brake Caliper w/ Retracting Piston is designed to provide a maximum amount of braking power packed into a minimal amount of space for easy mounting. The 150x1 is typically used with spindle mount front wheels and is designed to be mounted in either the three or nine Oclock position on a disc. Either the caliper or disc must float.

    The 150X1 series features a single piston with a patented piston reactor. The body is made of die-cast aluminum alloy. Friction linings are available in both hard and soft materials.

    Threads to hold the brake pad in are M4-0.7

    Requires type D.O.T. 3 brake fluid. ",44791.html

    specs on pad size for the 150 caliper:

    Brake lining "pucks" for your vintage Airheart 150x1 calipers
    1.460” O.D. and approximately .326 thick
    Features a recessed and countersunk attachment hole in center of puck
    These are available in hard and soft
    Last edited by TriNortchopz; 08-10-2020 at 6:46 AM.

  3. #3
    Senior Member

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    For the rear brake, do you know the diameter of the m/c piston and the diameter of the caliper piston(s)?

    The "on or off. to harsh" brake action is an indication of an improper m/c to caliper ratio;

    although this is for the front brake, info is relevant:

    Front Master Cylinder Ratio Chart

    "...the importance of master cylinder to wheel cylinder ratios. This critical ratio is of paramount importance in determining "feel". It has been my experience that there is a "sweet spot" in the range.
    I like ratios in the 27:1 range-2 finger power brakes, feeling some line and/or caliper flex. 23:1 is at the other end of the spectrum-firm.
    Ratios lower than 20:1 can result a feel so "wooden" as to have a toggle switch effect: nothing happens until the wheel locks.
    Disc and wheel diameters must be taken into consideration. A 10 inch disc working against an 19" wheel just doesn't have the leverage ratio that a 13 inch disc working a 17" wheel does...

    For 2 piston opposed calipers, I like ratios in the 27:1 range, feeling some line and caliper flex. For a firmer lever, use 23:1.
    I think ratios lower than 23:1 produce a lever feel so "wooden" as to have little, if any feel. Combine "low" leverage ratios with sticky pads, and unpredictable lockup is the result. The high effort required at the lever also results in undesired input to the bars.
    Single piston calipers are much happier in the 14:1 to 12:1 range.
    Disc and wheel diameters, as well as hand lever ratios, must be considered."

    See the ratio chart here:

    Front Master Cylinder to Wheel Cylinder

    "There's 3 main factors;
    MC piston size.
    The distance from the lever pin to the center of the cylinder
    # of pistons on the calipers/Size of caliper pistons = total surface area within the circumference

    How they go together in an equation,, I'm still clueless."

    Literally like a gear set or chain and sprockets. Say you have 15:45 gearing, that gives you a 3:1 final drive ratio, or 45 sprocket teeth divided by 15 sprocket teeth equals 3. Or one revolution of the rear wheel is three of the front.
    If you have a total area of say 4 caliper Pistons of 25mm each then you use Pi R squared of each piston, times four Pistons to get caliper "pushed" surface area,... then apply same Pi R squared to master cylinder bore size, then divide the big number by the small number to get the ratio."
    Last edited by TriNortchopz; 08-10-2020 at 7:18 AM. Reason: Pi R squared

  4. #4


    Thank you Sir, I will get to work.

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