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  1. #1
    Join Date
    Sep 2013
    Posts
    114
    Country Flag: Finland

    Default 1967 camaro brake problem

    I have 7/8 bore master ┤cylinder and double 8" booster, C5 front 13" calibers and 11" wilwood rear calipers. Pedal ratio is 1:6 i think. I will not get the brakes to lock no matter how much i push the pedal. is the master too big and where do i get smaller bore master? Is it possible to remove the booster entirely and make the brakes totally manual?

  2. #2
    Join Date
    Oct 2004
    Location
    Pflugerville, TX
    Posts
    57
    Country Flag: United States

    Default

    I had a very similar issue with my 68. I have a really large cam and just didn't have enough vacuum to consistently stop the car. It would never lock up the tires.

    I worked with Tobin from Kore3.com and he helped me swap everything over to manual and I LOVE IT. Had to get use to a slightly longer pedal travel with the 6:1 ratio, but it has great feel and I can stop on a dime. Here is what I have.




    I replaced all of the brake lines since most of mine were almost rusted through, which did require some bending and flaring to get everything to line up with the new master cylinder, but in the end it turned out really nice. Also, you will need to double check using the templates from Kore3.com to ensure your wheels will fit over the large rotors. My 18" Fiske wheels fit perfectly.

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  3. #3
    Join Date
    Sep 2013
    Posts
    114
    Country Flag: Finland

    Default

    Thank you really much! Im gonna order the same master cylinder and ditch the booster entirely! Thats exactly what i was looking for!

  4. #4
    Join Date
    Sep 2013
    Posts
    114
    Country Flag: Finland

    Default

    i ordered the sama master, hoping this will solve my brake problems for good and can remove the booster

  5. #5
    Join Date
    Nov 2014
    Location
    Alcoa, TN
    Posts
    22
    Country Flag: United States

    Default

    Quote Originally Posted by timopajala View Post
    I have 7/8 bore master ┤cylinder and double 8" booster, C5 front 13" calibers and 11" wilwood rear calipers. Pedal ratio is 1:6 i think. I will not get the brakes to lock no matter how much i push the pedal. is the master too big and where do i get smaller bore master? Is it possible to remove the booster entirely and make the brakes totally manual?
    Are you sure the pedal ratio is 6:1? 6:1 is achieved with the upper hole in the brake pedal being connected to the master cylinder. If you are using the upper hole, the geometry of the linkage dictates that the MC/booster combo must be bolted to the firewall squarely. If you are using the lower hole, (3.5:1 , which is to be used with power assisted setups such as the one you currently have) you must use plates which mounts the MC (and booster) on an uphill angle, from rear to front. I bring this up because an improper MC pushrod angle can cause bind or worse a failure to properly actuate the MC internal piston. This may be the root cause of your hard pedal.

    It would help if you post pictures of your current setup. Additionally, a 7/8" MC may be too small for you. I say this because your MC bore size is directly driven by you pedal ratio (which would be 6:1 upper hole for a manual setup) as well as your caliper's piston bore sizes and the number of each caliper's pistons. Typically for a manual brake system, you want a total hydraulic mechanical advantage of 20:1 to 50:1 depending on rotor diameter, pedal ratio, and pedal travel preference. 50:1 would result in more pedal travel, 20:1 would be less.

    Doing the math on your system, assuming C5 front calipers and dynapro 4 piston wilwood rear calipers, shows that even with 0 assist from the booster, the pedal effort should be low due to a hydraulic mechanical advantage of about 40:1. This leads me to believe you have a binding issue. Luckily this COULD be easily solved if you just remove the booster and bolt manual master cylinder directly to the firewall, using the upper pedal hole (6:1).

    I am using a 7/8 wilwood MC w/ SSBC d52 front calipers (dual piston 43mm floating type) on a 13" rotor and wilwood d154 calipers (dual piston 1.125" floating type) on a 12.2" rotor in the rear. For reference, my system's hydraulic mechanical advantage is 22:1. It was designed to initiate lockup at approx. 100lbs pedal effort (obviously this varies greatly depending on road condition and grade). This means that you SHOULD have a lighter pedal than mine, and it should travel more.

    Brakes are no joke, there a re plenty of well versed forum members here on the PT that are willing to help you, and hopefully save you time, money, and headache.
    Electrical/Mechanical Engineer
    1968 Camaro RS - Flat Black

  6. #6
    Join Date
    Nov 2014
    Location
    Alcoa, TN
    Posts
    22
    Country Flag: United States

    Default

    Quote Originally Posted by jprewitt View Post
    I had a very similar issue with my 68. I have a really large cam and just didn't have enough vacuum to consistently stop the car. It would never lock up the tires.

    I worked with Tobin from Kore3.com and he helped me swap everything over to manual and I LOVE IT. Had to get use to a slightly longer pedal travel with the 6:1 ratio, but it has great feel and I can stop on a dime. Here is what I have.




    I replaced all of the brake lines since most of mine were almost rusted through, which did require some bending and flaring to get everything to line up with the new master cylinder, but in the end it turned out really nice. Also, you will need to double check using the templates from Kore3.com to ensure your wheels will fit over the large rotors. My 18" Fiske wheels fit perfectly.

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    I LOVE those wheels. Fikse's have to be some of the best wheels out there.

    Are those KORE 3 aluminum hubs?

    Thanks in advance
    Electrical/Mechanical Engineer
    1968 Camaro RS - Flat Black

  7. #7
    Join Date
    Sep 2013
    Posts
    114
    Country Flag: Finland

    Default

    Yes My Master IS on uphill angle and IS assembled The rigjt way. I checked The binding many times and sound none. The pedal is light during normal driving but when on full throttle its rock hard. So there is not enough vacuum. My friend has 68 Camaro with same kind of setup and the same issue. He hooked electric vacuum pump and now Oy Works.

  8. #8
    Join Date
    Sep 2013
    Posts
    114
    Country Flag: Finland

    Default

    Pedal ratio IS lower then 6:1. I checked and its on The lower hole. I bought 7/8 manual Master and try to fix the issue with that. Thank you all for replyes!

  9. #9
    Join Date
    Oct 2018
    Location
    San Jose, CA
    Posts
    327

    Default

    That will be a major difference - lower hole vs. upper hole. I would make no other changes from that and see where you are.

    Sleeper68 - what is the formula you are using to calculate the mechanical advantage numbers?
    I've always done this / seen this done in torque value, not mechanical advantage. Interested to see what those equations look like if you can share them.

    Also WRT the C6 brakes and manual - you can make them work with a small enough master (I'm actually surprised 7/8" is small enough) but those brakes front and rear have a pretty small piston area for a manual brake system. Generally you want something up over 5 sq-in on the front calipers.

    1971 Camaro - 406
    2016 Camaro SS convertible
    2018 Colorado 4x4




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