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Thread: Brake issue

  1. #1
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    Brake issue

    I am having a hell of a time with the brakes on this car. I got the standard front brakes and the upgraded Mustang rears. I did not go with the wildwood brakes.

    I cannot get the front brakes to lock up.

    I bled the brakes and the master cylinders. I had a strong pedal. I have rebled the brakes many times and haven't gotten air on any attempt.

    I have moved the cylinder arms in all configurations (front all the way out and all the way in). I have also moved the brake balancer in both directions.

    It stops well and I get weight transfer to the front of the car. However the rears lock up and the fronts won't. Even if I dynamite the brakes past the rears locking up to see if the fronts do.

    Am I missing something?

  2. #2
    Senior Member Gordon Levy's Avatar
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    Check the master cylinder size you are running the fronts and the rears from. If you are doing this in gokart stage you probably won't get the brakes bedded properly. I would not to weird about it untill the car is truly drivable.
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    I used the wilwood ones provided with the complete kit. I was under the impression they were the same size.

  4. #4
    David aka Ducky2009 Ducky2009's Avatar
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    I used the FFR supplied (2 piston) calipers on the front and single piston equivalent (Mustang GT) rears, and the Wilwood footbox/dual master cylinders. Couldn't get any of the wheels to lock up. Bled the brakes several times. Didn't like it. Too much Go and not enough STOP! Ended up adding vacuum power brakes. Same as what Whitby sells. I purchased the components separately, but had to made a steel brake pedal. Let me know if you want the part numbers.

    FYI.... I installed the body, unpainted, and drove a few hundred miles. Never liked the breaking. Took the body off when I painted it and installed the break s then. I know someone who did it, but extremely difficult to install with the body on.
    Last edited by Ducky2009; 06-17-2019 at 08:03 PM.
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    Body is on and I don't want to take it back off.

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    Seasoned Citizen NAZ's Avatar
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    Take Gordon's advice above. The break pedal effort is determined by the lever arm of the brake pedal and by the difference in size between the M/C and the caliper piston size. The smaller the M/C piston is compared to the caliper the more mechanical advantage -- it's a simple ratio thing. The larger the pedal arm ratio the more mechanical advantage. But it's usually easier to adjust the M/C size than the pedal lever ratio.

    The brake pedal effort will affect breaking performance -- more effort = less brake pressure = less caliper clamping force = less braking performance. You can see where this is going... If the pads clean are properly bed, the rotors are in good shape, and nothing wrong with the calipers then a smaller diameter M/C will increase braking force. But at the cost of increased pedal travel.
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    Quote Originally Posted by Ducky2009 View Post

    I installed the body, unpainted, and drove a few hundred miles. Never liked the breaking. Took the body off when I painted it and installed the break s then. I know someone who did it, but extremely difficult to install with the body on.
    Quote Originally Posted by Dthquazi View Post
    Body is on and I don't want to take it back off.
    These are common problems.

    I think too many people get ahead of themselves on the build, and end up (with the body on) at "I don't like the way it works" - steering / braking / built or bought too much / not enough engine / rear gear / etc.

    There is a long list of things you can (easily) get "wrong" on these cars - despite everyone's best efforts - differing expectations + experience levels (and many other factors + variables).


    It's best to get happy with all that before the body goes on - many states / countries aren't very "friendly" for that - and many builders / buyers don't have the patience for that.

    It's unfortunate.

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    Yeah, a fair amount of go carting wasn't an option for me on this one.

    So what it sounds like is with the current setup, this is to be expected. I need a different sized master cylinder for the front to get better stopping on the front. Or switch up the front calipers.

  9. #9
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    If you are using the FFR supplied components, you might want to try better rotors and pads. A number of people have had major improvements using the "powerstop" stuff - and the price is quite reasonable - check "Rockauto"

  10. #10
    Senior Member CraigS's Avatar
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    I believe the standard MCs are still 3/4 front and 5/8 rear. Check yours and confirm this w/ other MkIV owners. Change if needed. Then order Hawk HPS or HPS5.0 pads for the front. HPS is the original great compound w/ more grip than most and very little dust. I mention the HPS5.0 because it is a newer equivalent and not all pad sizes are available in both. Hawk has two other compounds w/ even more grip but they dust a lot more too.
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  11. #11

    Steve >> aka: GoDadGo
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    Quote Originally Posted by CraigS View Post
    I believe the standard MCs are still 3/4 front and 5/8 rear. Check yours and confirm this w/ other MkIV owners. Change if needed. Then order Hawk HPS or HPS5.0 pads for the front. HPS is the original great compound w/ more grip than most and very little dust. I mention the HPS5.0 because it is a newer equivalent and not all pad sizes are available in both. Hawk has two other compounds w/ even more grip but they dust a lot more too.
    Craig is spot on regarding the MC Sizes and the vastly improved performance of the Hawk Pads.
    I've got the standard Mustang front brakes with Explorer/Ranger rears and you can really feel the difference with the Hawk pads.
    I was really surprised that they made them for my rear brakes since those were for their Miniature Truck Applications.

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    Quote Originally Posted by Dthquazi View Post

    So what it sounds like is with the current setup, this is to be expected. I need a different sized master cylinder for the front to get better stopping on the front. Or switch up the front calipers.
    Typically, people seem to more commonly have trouble with the fronts locking early - just from the difference in sizes between the rotors and especially the caliper pistons - front caliper piston area is considerably larger than rear caliper piston area and this makes a huge difference.

    I'm guessing something isn't quite right with your front calipers, or with the way the front MC / balance bar is set up.


    But all that is pretty hard to determine much about with the body on.

  13. #13

    Steve >> aka: GoDadGo
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    Quote Originally Posted by mike223 View Post
    Typically, people seem to more commonly have trouble with the fronts locking early - just from the difference in sizes between the rotors and especially the caliper pistons - front caliper piston area is considerably larger than rear caliper piston area and this makes a huge difference.

    I'm guessing something isn't quite right with your front calipers, or with the way the front MC / balance bar is set up.


    But all that is pretty hard to determine much about with the body on.
    Hey Mikeee,

    Just Spit Balling On This Comment In Between Conference Calls:

    All the complete kits are or were recently coming with 3/4" front with 5/8" rear MC's....We probably need to do a little math to figure out how much fluid is really needed to move each brake piston or pistons....Since these cars typically have a 45/55 or 50/50 in my case weight distribution, we probably need very similar if not identical set ups on both ends of the cars.

    Yes the balance bar is there to fine tune the set up, but with so many combinations out there we really need to ask ourselves what do we really need to stop these suckers properly if we choose to avoid going down the power brake and proportioning valve path.

    Hummmmmm!

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    Any way to tell the difference in sizes now that they are installed? I am 90% sure they were the same part number (on the box) when putting it together.

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    How much trouble to just swap the hard lines from one master cyl to the other?
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    Steve >> aka: GoDadGo
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    Quote Originally Posted by Dthquazi View Post
    Any way to tell the difference in sizes now that they are installed? I am 90% sure they were the same part number (on the box) when putting it together.
    Mine were marked 3/4" (.75) and 5/8" (.63) on the outside of each M/C.
    Last edited by GoDadGo; 06-18-2019 at 10:27 AM.

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    Quote Originally Posted by GoDadGo View Post

    We probably need to do a little math to figure out how much fluid is really needed to move each brake piston or pistons.

    Since these cars typically have a 45/55 or 50/50 in my case weight distribution, we probably need very similar if not identical set ups on both ends of the cars.

    Yes the balance bar is there to fine tune the set up, but with so many combinations out there we really need to ask ourselves what do we really need to stop these suckers properly if we choose to avoid going down the power brake and proportioning valve path.
    There's a lot of math that I've worried about in the past - but it almost always comes back to variables in individual components / installation + individual expectations + driving styles (how the operator uses the brake pedal).

    Typical Detroit front / rear brake setups usually tend toward 75/25 balance engineered into the size of the rotors / pads / pistons.

    These cars usually need a little more than 25% in the back - but not much, because if you have grip you still get a lot of weight transfer in a panic stop.

    And if your typical "most violent panic stop" involves running a high compression engine up to redline in second gear and dropping throttle and stepping on the brake hard with sticky tires (autocross) - you'll soon find out you're back real close to needing 75/25 (because you stepped off the throttle at redline and you're getting a bunch of engine braking help in back).


    Here's an online brake bias calculator :https://brakepower.com/

    Here's a downloadable Excel spreadsheet : http://vitessesteve.co.uk/Resources/GTBrakingmodel.xls

    Those are for calculations involving a dual MC with balance bar.


    Many don't realize that a conventional tandem MC will produce double the pressure for the same input as a dual MC (more properly - full pressure on both circuits). This is handy if you get back to where you can use the bias originally engineered into the components you're using.


    One of the biggest variables in the whole thing is how you step on the brake pedal - they are sprung so tight and such short wheelbase, a lot of weight transfer to be had - a good case can be made for ABS because the weight transfers so quickly (and changes the whole formula).
    Last edited by mike223; 06-18-2019 at 11:23 AM.

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    Quote Originally Posted by Railroad View Post
    How much trouble to just swap the hard lines from one master cyl to the other?
    That's the plan. Not hard at all but pretty messy. I have gotten so good and lifting, taking the wheels off, and bleeding that it shouldn't take much time at all.

    Thanks godadgo, I will check them out for markings!

  20. #19
    Senior Member edwardb's Avatar
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    I've talked to a couple of builders who have recently received their Roadster kits. Looks like FF is supplying two 3/4-inch masters now. Apparently no longer doing the smaller 5/8-inch rear MC. If that's the case for all, back to how they supplied them several years ago. That adds to this discussion perhaps.

    Count me as also agreeing go-kart is not the time to be evaluating brakes. Aside from being wildly illegal, my experience is it takes several hundred miles at least plus the specific bedding process. First impressions before then are not reflective of how they will be later. Manual brakes, in most cases, can be made to work acceptably in my experience. Whether better rotors, better pads, break-in, whatever. But in the end they will always require a much heavier pedal than power. That alone is something many aren't prepared for or find acceptable.
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    Quote Originally Posted by edwardb View Post

    Count me as also agreeing go-kart is not the time to be evaluating brakes. Aside from being wildly illegal, my experience is it takes several hundred miles at least plus the specific bedding process.
    I should qualify my earlier comments with the fact that my ~2500 miles of go-karting and autocrossing the go-kart was mostly licensed + insured with brake lights + turn signals temped up on the frame.

    I had read enough "tales of woe" to refuse to start bodywork until I was completely happy with all the mechanical systems.

    I'm certain that's not an option in many states.



    In those situations I would suggest trailering it to a parking lot or industrial park on weekends (and don't make a nuisance out of yourself while you're there).

    It's a lot easier to check + modify before you cover all that up with bodywork.

  23. #21
    David aka Ducky2009 Ducky2009's Avatar
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    Quote Originally Posted by Dthquazi View Post
    I used the wilwood ones provided with the complete kit. I was under the impression they were the same size.
    In early 2017, the supplied Wilwood master cylinders were 5/8 (.62) and 3/4 (.75). Not sure when your kit was delivered and what sizes they might have been at that time. See the pic for where the size is located on the MC.

    Wilwood Master Cylinder.jpg
    Last edited by Ducky2009; 06-18-2019 at 02:43 PM.
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    Ok. It looks like my memory was not correct. I have two different sizes with the 3/4 in the front and the 5/8 in the rear.

    I will look at different pads.

    I'm not worried or dissatisfied with the pedal pressure. I just want the vehicle to stop in the most efficient manner for the setup I have. Not being able to lock up the fronts worries me. I do get significant front braking based on weight transfer and stopping distance (based on when I initially started and the bias was to the rear).

  25. #23
    Senior Member CraigS's Avatar
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    Can you take a picture showing the position of the balance bar and note which cylinder is which also.
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    I had 0.75 both F & R originally installed. I recently changed to 0.70 and 0.50. Feels much better as pedal travel increased. However, now it travels a little past my accelerator pedal when hard braking only. As a result pushing the brake hard I end up depressing the accelerator too. Dang pedals are too close together or I have big feet.
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    Steve >> aka: GoDadGo
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