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    1. #1
      Join Date
      Sep 2013
      Posts
      159
      Country Flag: Finland

      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
      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
      159
      Country Flag: Finland
      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
      159
      Country Flag: Finland
      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
      East Tennessee
      Posts
      163
      Country Flag: United States
      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
      East Tennessee
      Posts
      163
      Country Flag: United States
      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
      159
      Country Flag: Finland
      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
      159
      Country Flag: Finland
      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
      523
      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 / T56
      2016 Camaro SS convertible
      2018 Colorado 4x4

    10. #10
      Join Date
      Jul 2018
      Location
      Ontario Canada
      Posts
      69
      Country Flag: Afghanistan
      Curiosity I have a 1967 Firebird with corvette c5 brakes front and rear would a 7” booster and 7/8 willwood master work for that?

    11. #11
      Join Date
      Oct 2018
      Location
      San Jose, CA
      Posts
      523

      1967 camaro brake problem

      I would go with the factory C5 master sizing. Pretty sure it’s bigger. 1” I believe.
      Maybe just get a whole C5 factory setup.
      1971 Camaro - 406 / T56
      2016 Camaro SS convertible
      2018 Colorado 4x4

    12. #12
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      163
      Country Flag: United States
      Quote Originally Posted by c4racer2 View Post
      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.
      I agree, I would think the 7/8" Wilwood MC could be affixed to the firewall without needing to order parts.

      Regarding your mech. advantage question: Hydraulic mechanical advantage is dependent on a ratio of areas alone. Since the fluid displaced volume and pressure is assumed to be constant between the input and output side, the only thing that varies is force and area.

      So, total input side area would be the piston area of the master cylinder which calculated as: pi*((1/2)*(d_piston))^2 = pi * ((7/8")/2)^2 = ~0.6 sq.in.

      Now for the output side: front piston area, 4pistons*pi*(40.5mm/25.4/2)^2 = 7.99sq.in. and rear piston area 8pistons*pi*(1.75/2)^2 = 19.24 sq.in. and total output area = 27.23 sq.in.

      Total Hydraulic mechanical advantage= output area / input area = 27.23 sq.in / 0.6 sq.in = 45.4:1

      The reason I mentioned the hydraulic mechanical advantage is because we did not know what pedal ratio was being used. Additionally, assumptions were made regarding the piston diameters since the exact calipers being used were not defined. Normally one would cite the mechanical advantage including the pedal ratio.

      timopajala, including your pedal ratio, with no assist from the booster, your total mech advantage comes out to 45.4:1 * (3.5:1) = ~160:1

      For reference, my mechanical advantage is 21.7:1 8 (6:1) = ~130:1

      This means should have a lighter pedal than me, with the assertion that my assumptions on your piston diameters is correct. Since you are feeling a hard pedal and the numbers say you shouldn't have one, I am led to believe my assumptions are incorrect somewhere. Please provide more detailed info regarding what calipers you have (pictures and part numbers would help), as the piston diameters have a huge effect on brake feel and master cylinder sizing.

      c4racer2, output torque of the braking system is an important value to be concerned with, but it is more of a design input as opposed to a design output. What I mean by that is this:

      If I want to stop my 3200 lb Camaro in 100ft from 60 mph, I have to dissipate a certain amount of energy in a certain distance. We know that kinetic energy is calculated as: (1/2)*(mass_vehicle)*(speed_vehicle)^2 . This comes out to be 384,795 lbf-ft of energy to be converted to heat energy by the brakes (remember energy can neither be created nor destroyed).

      Energy is also called work in the engineering world. One can interpret this 385,000 lbf-ft of energy as applying 385,000 pounds of force over a distance of 1 foot OR 1 pound over a distance of 385,000 feet. BUT, what if one was to apply some other amount of force over a distance of 100 feet? This is where obtain our required constant braking FORCE from the desired stopping distance.

      So, the braking system needs to apply a force of approximately 3848 pounds over a distance of 100 ft in order to stop the car (384795 lbf-ft / 100 ft = 3848 lbs).

      The mechanism for application of brake torque is through the rotor and into the wheel, then into the tire. All 4 tires together have to apply a total of 3848 lbs against the road to stop the car. Assuming 75% front 25% rear torque split (due to the available normal force at the tires as a result of weight transfer under braking) and a 25.7" tall tire the brake torque requirement would be:

      Front Wheels Each: 3848lbf*0.75*0.5*(25.7/12/2) = 1545 lbf-ft
      Rear Wheels Each: 3848lbf*0.25*0.5*(25.7/12/2) = 515 lbf-ft

      Assuming a front rotor effective diameter of 11" and rear effective diameter of 9" (this is where the center of the pad acts on the rotor, corresponding to a 13" front rotor and 11" rear rotor):

      Front Caliper Braking Force Each: 1545lbf-ft / (11"/12/2) = 3370 lbf
      Rear Caliper Braking Force Each: 515lbf-ft / (9"/12/2) = 1373 lbf

      Now to calculate line pressure from Caliper piston area, pad type, and caliper type (floating or fixed, must divide by 2 for floating calipers):

      Front Caliper Required Line Pressure: 3370lbf / 2 / 4.5 sq.in. / 0.4 = 1056psi
      Rear Caliper Required Line Pressure: 1373lbf / 2 / 1.99 sq.in / 0/4 = 862psi

      It can be noted that an adjustable proportioning valve would be needed to limit rear line pressure to 860 psi to prevent rear lockup.

      Using a 7/8" Master cylinder and a 6:1 pedal ratio, the pedal effort from the driver would be:

      1056psi * 0.6 sq.in. = 633.6 lbf on the MC pushrod
      633.6 lbf / (6:1 pedal ratio) = 105.6lbf

      This is assuming constant braking force (and torque) as well an instantaneous reaction time and application of the brakes. Obviously this is not realistic, but it gives you a staring point for the absolute bare minimum for brake torque requirement.

      100 lbs of pedal effort is the generally accepted rule for threshold braking when using non-assisted, manual system, and it is the number I designed my system around. If one is used to new cars with very touchy, light brake pedals, then this may be too much. Something to keep in mind.

      As you can see this is a quite lengthy calculation series and requires many assumptions. Just a 10% change in brake pad "grippines" (also called friction coefficient) has a direct 10% effect on pedal effort. Tire diameter, pitch center, CG height, wheelbase, Tire fiction coefficients, brake pad friction coefficients, piston area, dimensions of the brake rotor, caliper type floating or fixed, etc have huge effects on the system. I am glad to perform this calculation for you, timopajala, or anyone else, but you can see I will need very detailed info about the vehicle in question.

      Hope this helps.

      Ryan
      Last edited by Sleeper68; 07-23-2019 at 03:35 AM. Reason: typo
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    13. #13
      Join Date
      Sep 2013
      Posts
      159
      Country Flag: Finland
      i think my booster was bad, it was really hard to push when i removed it from my car. To the piston sizes, i have 1.75" pistons in the front, corvette c5 calibers. I have wilwood forged 4 piston calibers in the rear 1.38" pistons. I might have calculated the piston area wrong but if you know how to calculate those and my brake pressure that would be really nice! brake pedal is 6:1 ratio.

    14. #14
      Join Date
      Sep 2013
      Posts
      159
      Country Flag: Finland
      Well after The brake swap not impressed. Brake pedal is really hard to push and car stops really Bad. Could Air on The system do that? Have to bleed More of that helps. I have stock C5 brake pads, should i try better ones?

      Proportion valve not adjustet, could that Make difference? Maybe too much brake force to rear and brakes are stiffer?

    15. #15
      Join Date
      Sep 2013
      Posts
      159
      Country Flag: Finland
      Well i Bled The brakes today again with My Brother, no The pedal goes almost to The floor when i press IT hard. Have not tested It in Road yet. IS it safe to drive when The pedal goes almost to The floor? No idea how strong IT Will brake. I swapped ceramic brake pads to The front id that would Helo.

      I noticed during bleeding that The Master moves very little brake fluid to The rear Even when The proportion valve IS fully open. I have bleeder bottle that like 30mm thick and there comes like 3mm liquid on one bleeding time. It takes 15 pedal strokes to heti half from The brake Master cylinders volume.

      IS The Master broken of IS IT too small for My brakes?

    16. #16
      Join Date
      Jun 2012
      Location
      Chicago burbs
      Posts
      247
      Country Flag: United States
      Quote Originally Posted by timopajala View Post
      Well i Bled The brakes today again with My Brother, no The pedal goes almost to The floor when i press IT hard. Have not tested It in Road yet. IS it safe to drive when The pedal goes almost to The floor? No idea how strong IT Will brake. I swapped ceramic brake pads to The front id that would Helo.

      I noticed during bleeding that The Master moves very little brake fluid to The rear Even when The proportion valve IS fully open. I have bleeder bottle that like 30mm thick and there comes like 3mm liquid on one bleeding time. It takes 15 pedal strokes to heti half from The brake Master cylinders volume.

      IS The Master broken of IS IT too small for My brakes?
      timopajala,I've spent a few days trying to digest this post, and I think there's been some good advice.I want to say that, first, brakes may be one of the most aggravating systems to work on/troublshoot. It's easy to start just throwing stuff at the wall and see what sticks, but often times that leads to extra information that hides the true issue. There's a lot of good guys on here that can help(and are trying), so I think a few things would help.
      1) post a few pics of your setup, including the Master cylinder, booster, and pedal linkage from under the dash.
      2) list the specs for the original and the latest setup:
      Master cylinder diameter Original Setup Current Setup
      Booster Type
      Front caliper piston number
      Front caliper piston Bore
      Rear caliper piston number
      Rear caliper piston Bore
      Pedal ratio
      Additionally, what pads are you using? autozone pads probly aren't going to cut it here(they won't cause a "hard " pedal, but probly don't have the CoF to crank out good numbers. I run wilwood BP-20's and those don't do anything until after the second stop when they are cold.

      What sticks out to me is that you confirm that the booster and master are instaleld up at an angle, yet still say the pedal ratio is 6:1. if it is indeed up at an angle, then the pedal rod needs to be in the lower hole.

      And no-I wouldn't drive my car with a squishy pedal ever.
      I hope this helps,a nd I hope you can come back with the info so the rest of us can continue to help.

      1969 442 6.0L LQ9 T56
      Fab9 w/ custom 3 Link conversion
      FAYS2 Watts link
      Thanks to Mark at SC&C for his honesty and passion for the sport, and Ron Sutton for the wealth of knowledge that has helped shape so many of the cars on this site.

    17. #17
      Join Date
      Aug 2015
      Location
      NJ
      Posts
      282
      Country Flag: United States
      I have a 68 with a 572bb. I have 12" wilwood 6 piston up front and 12" 4 piston in the rear. I have a huge cam and no vacuum so I too went with a full manual setup, but I have a 1" bore mc. I ran full stainless steel lines and stainless braided lines to the front calipers and from the rear line to the rear set up.

      Squishy pedal is NOT safe.

      Check all your lines for kinks or crimps. If they are original, it is cheap enough to replace them all for piece of mind.

      Also replace all rubber lines off the main lines to the front calipers with stainless braided. Rubber can expand especially if older causing a squishy pedal. Replace the one in the rear too!

      Did you bench bleed your mc? If not you will have to do what I did and run a line from the caliper bleeder to the mc and all 4 corners one at a time. You will use alot of extra fluid, but it was worth it for me because everything is jammed in there.

      Lastly do not use the new silicone type brake fluid, I believe referred to as dot 5. That will cause a squishy pedal too

      Good luck bro
      '68 Chevy Camaro Pro-tour ~ project DMENTD
      '57 Chevy 3100 Pro-tour pickup ~ under construction

    18. #18
      Join Date
      Sep 2013
      Posts
      159
      Country Flag: Finland
      Thanks for The reply. Yes i bench Bled The Master but i think theres something wrong with The Master. Lines are new from front to Back.

      No kinkcs of nicks on them. They worked fine with The old Master but not enough vacuum.

      With this new booster vacuum won't Be problem.

      Just made brackets for it today and gonna Bolt averything together.

      Gonna bench bleed The Master also before install.

    19. #19
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      163
      Country Flag: United States
      Quote Originally Posted by timopajala View Post
      Thanks for The reply. Yes i bench Bled The Master but i think theres something wrong with The Master. Lines are new from front to Back.

      No kinkcs of nicks on them. They worked fine with The old Master but not enough vacuum.

      With this new booster vacuum won't Be problem.

      Just made brackets for it today and gonna Bolt averything together.

      Gonna bench bleed The Master also before install.
      Why will the new booster eliminate your issue? a boosted system requires a 3.5:1 ratio, which means the 6:1 ratio you described earlier won't work.

      jetmech442 is right, we need pictures and specifications of your brake system to effectively help you.

      PLEASE fill in the blanks so we can help you, otherwise we are all just shooting in the dark so to speak.

      ................................................Or iginal_Setup.......Current_Setup
      Master cylinder diameter...........[____________].....[_____________]
      Booster Type...........................[____________].....[_____________]
      Front caliper piston number.......[____________].....[_____________]
      Front caliper piston Bore...........[____________].....[_____________]
      Rear caliper piston number........[____________].....[_____________]
      Rear caliper piston Bore............[____________].....[_____________]
      Pedal ratio...............................[____________].....[_____________]

      Required pictures: engine bay showing MC and booster, brake pedal showing connection to master cylinder/booster pushrod, and one of each brake caliper with the hoses in view.

      The pedal should NOT go to the floor, nor should it be hard. It should not take more than 450 N (45kg) to stop the car quickly.

      The squishy pedal that goes to the floor means there is air in the lines or brake fluid leak. Try re-bleeding and checking for leaks.

      Ryan
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black

    20. #20
      Join Date
      Sep 2013
      Posts
      159
      Country Flag: Finland
      Thanks for The reply! Well after several bleeding trials with vacuum pump etc we could not The brakes to Work. I contacted wilwood about The matter and posted My pedal ratio and piston sizes etc to them.

      They Said that The Master is too little and need to upgrade bigger one.

      Well i did not buy bigger one because i was not pleased The pedal force Even with The smaller one and going bigger makes the pedal stiffer.

      I desided to swap gen5 Master and booster after that, because i had those allready and did not need to buy anything.

      I made My own brackets and bled the system today and i must say, what i difference! The car stops like new cars, pedal is really gentle to push and all wheels lock Even in asfalt If needed.

      The wilwood Master is broken internally i think. We could not get any fluid out even with vacuum pump from The rear calibers. Only pushing The pedal fluid flowed out The bleeding nible.

      After The Master cylinder swap The fluid came normally out The rear calibers.

      One bleeding sequense and The whole system was ready.

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