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Thread: Hydraboost or 13 inch disc to upgrade braking

  1. #11
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    Bitchin', yes I meant master cylinder. Will edit.

    A pressure gauge will certainly help sort out the variables.

  2. #12
    Registered Member JT56's Avatar
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    My current setup on my car is the 10.5 metric on the fronts(I know old stuff), Hydratech HB, with 1" bore MC (2006 GTO), external pv and strange brakes (4 piston). I used to have vacuum pump(SSBC) on my car, 1 1/8 MC (CPP) along with 2004 cobra brakes on the rear. I never checked the with pressure gauge, but the car stopped pretty well. No complaints and did a lot of street cruising too. After mini tub and double bead locks I had to change the rear brakes so now the car stops on a dime and gives back change. My future plan is to upgrade the front brakes to something that looks a little better and lighter. However, no problem with the way it stops now. As everyone else has said, start with a pressure check to see what you have. If the budget calls for it...do both.

  3. #13
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    Well JT, looks like that's good input for bihili, since you have a boosted engine and similar front brakes.

  4. #14
    Registered Member JT56's Avatar
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    Quote Originally Posted by Bihili View Post
    I am not satisfied with the current 10 1/2 front disc and rear drums on 12 bolt rear end.
    Because of the small supercharger I have an electric vacuum pump and additional tank which produces 18 inches of vacuum.
    This is barely enough for the vacuum booster.
    It feels like the brakes will not lock up, maybe because of the large tires, 245 & 295's

    Which upgrade do I need?
    Larger front disc or hydroboost?
    The SSBC was setup for 24" of vacuum so a little more than the 18. I would still check brake pressure first. I have one of the reverse bleeders and it does help with getting them bleed. Also remember the skinnier the front tire is the less contact surface you have for braking. Looks like a race car and helps cut down rolling resistance, but not great for stopping a heavy car.

  5. #15
    Registered Member Bihili's Avatar
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    I found a couple of PSI gauges. Now I need to figure out the adapters I need to connect to the front brake line at the caliper to test the pressure.
    The first thing I want to test is disconnecting the vacuum pump regulator.
    Just wire the vacuum pump to run continuously and see if it will increase the amount of vacuum and then maybe a test drive if I have more vacuum.

    Bill 1957-427-177-6-410

  6. #16
    Registered Member 55 Rescue Dog's Avatar
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    I've found out that permanently mounted F/R brake pressure gauges to be extremely helpful on a hot rod. Of course on my 55 I will come up with a cleaner install than this one.IMG_2620.JPG

  7. #17
    Registered Member Bihili's Avatar
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    Update:
    After installing a PSI gauge to the front caliper using the bleeder hole here are the stats.
    With engine off my 125lb wife could only get 400 PSI.
    I was barely able get 600 PSI with engine off.
    With the engine running and 18 inches of vacuum from the electric vacuum pump I was able to get 750 PSI.
    After I changed the vacuum pump to run continuously it is producing 20 inches of vacuum and was able to get 800 PSI.
    Now before you criticize my vacuum pump just remember how many Hybrids and other vehicle on the road today use electric vacuum pumps.
    This is a standard GM pump.
    Other stats: CPP master cylinder 1 inch bore, CPP dual 8 inch diaphragm, CPP proportional valve, linkage 1 inch lower on pedal, rear drums on 12 bolt and 10 1/2 inch rotors.
    The additional vacuum made a improvement so I will try the skid test and see if I can lock them up.
    Bill 1957-427-177-6-410

  8. #18
    Registered Member chevynut's Avatar
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    To me 800 PSI seems low. I'm curious how much force you're able to put on the pedal. More vacuum doesn't appear to help that much either.

    FYI the spec for the front of a C4 is 1250 PSI at 100 lb on the pedal or 12.5 times pedal effort. I don't know what it is for other cars. The force at the piston depends on piston area.

    I found this online:

    "Typical brake line pressures during a stop range from less than 800psi under "normal" conditions, to as much as 2000psi in a maximum effort. "

    What is your pedal ratio?
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension

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  9. #19
    Registered Member JT56's Avatar
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    If the system is all in working order...Cnut I think your on to something with the pedal ratio

  10. #20
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    Thing is, the pedal ratio you can achieve without creating binding in the linkage is limited. On a 55-57, a flat mount booster or a manual setup is a setup that works well both with the geometry and with potential brake line pressure with the stock 6:1 ratio. An angled mount lends itself to a 4:1 ratio.

    You also can work with master cylinder bore size to optimize this. More pedal ratio = more line pressure but more pedal travel. Smaller master cylinder bore = more line pressure and more pedal travel. This for a given caliper bore.

    100 pounds pedal force is a lot. I think this is panic stop territory, not normal driving territory.

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