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Thread: brake line pressures

  1. #1
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    brake line pressures

    does anyone know what psi readings should be at front power disc calipers and rear drum brake cylinders. 57 chevy. thanks any info will be appreciated

  2. #2
    Registered Member chevynut's Avatar
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    It depends on the force applied to the pedal, the pedal ratio, the booster multiplication factor, and the size of your master cylinder bore. The stock pedal ratio is about 6 to 1.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


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  3. #3
    Registered Member chevynut's Avatar
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    What problem are you trying to solve?
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  4. #4
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    car not stopping like it should. plenty of vacuum 20+inches.pedal really not like I think power brakes should be. brakes bled several times pump up method and gravity bleed. confident no air in system. with brake pressure gauge I read 450 psi at rear wheels on braking and 500 psi if I really stand on pedal. 900psi on front calipers. cannot lock up wheels from 35 mph. everything from front to rear brakes has been replaced and I mean everything. this is a kit which included all new parts. kit came with adjustable prop valve. with valve open drum brakes on rear should lock and then adjust valve to decrease pressure to equalize braking but when adjusting to decrease pressure braking is worse which is understandable an pressure drops to 250 psi midway between open and close so I pretty sure valve is working. I have been in touch with supplier but not much help. easy install with also ssbc pump. thanks for input. grasping for STRAWS.

  5. #5
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    Most brake setups require 1000-1500 psi to get good performance. This will vary however. Some may need 2000 psi.

    Several things affect line pressure. Master cylinder bore size and pedal ratio are the usual ways of changing it if needed.

    You might tell us what you have for master cylinder, booster, and calipers. The system must have all the components match.

    You mention SSBC. SSBC calipers have pretty small bores, and this means you need higher pressure than some others.

  6. #6
    Registered Member chevynut's Avatar
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    900 PSI in front does sound low if you're really standing on the pedal. Just to give you an idea, a 1990 Corvette is supposed to have 1250 PSI in front and 750 PSI in the rear with 100 pounds of pedal force.

    Here's a link to the stock 57 brake specs:

    http://chevy.oldcarmanualproject.com...esto/57038.htm

    The overall manual brake ratio is supposed to be 29.1:1. That means if you apply 100 pounds of brake force, you should theoretically get 2910 PSI....at 50 pounds it should be 1455 PSI.

    What size vacuum booster do you have? What is the master cylinder bore size? Do you have a link to the kit you used?
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  7. #7
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    I thought I replied yesterday but don't see it.

    I agree with Cnut, but as a practical matter, putting 100 pounds on the brake pedal is probably a bit beyond reality. At least in normal driving. Maybe you get close sitting in the shop, or maybe a true panic situation.
    Last edited by Rick_L; 09-22-2013 at 06:21 PM.

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