My Brakes Are Too Good!!

Discussion in '1965 - 1973 Classic Mustangs -General/Talk-' started by Ktga67, Oct 3, 2013.

  1. Here's the problem, my brakes are Very touchy!! I had 4 wheel drums and upgraded to the original style bendix booster and a 92 v8 fox master cylinder (because the ports exited on the correct side for my application). The power brake petal was also swapped in at the same time, so thats when they went from so so brakes to jar your teeth out brakes. I thought it might be because of the drum/power brake combo so when I changed out my rear end I went ahead and did a 4 wheel disk brake conversion with explorer disks out back and the CSRP kit up front with the original style 4 pot calipers. Even more touchy now, go figure!! Anybody have any suggestions or ran into the same issue??
  2. what year mustang is this?
  3. It's a 67
  4. Your master cylinder bore is too small making the pedal extra responsive.

    Can you tell me the piston sizes of the calipers you are using front and rear? If not...can you tell me year and model car they are off?

    Sent from my iPhone 4S using Tapatalk
  5. I don't know the size bore of the pistons, but the fronts and the original style kh 4 piston calipers from the crsp kit and the rears are from a 96 Explorer. Crsp gave me the pn# for the master cylinder I have on it now, I believe it's made for a ranger/b3000.
  6. The MC I'm using is made for a 90-94 Explorer/ranger and has a 1" bore according to advance, couldn't find any markings on it.
  7. The 92 v8 mustang MC has a 21mm bore. That's 0.83"

    The 1" might get you where you need to be. Hard for me to say really because my brake swap experience is in the 79-93 cars.

    Changing only the MC, the larger a the MC bore for your brake setup, the firmer the pedal will be. The ford explorer rear disks are rather large pistons (48mm according to so you might need to go larger.

    I do not know the brake line setup of the classics, but i do know two larger master cylinders if need be. 1994-1995 mustang GT/V6 is 1 1/16". And the 1984-1986 mustang SVO turbo uses a 1 1/8" MC
  8. Thanks for your input Mustang5L5, in your experience with the fox mustang's brake swap what caliper's front/rear sere you using?
  9. Update:
    I contacted CRSP about my problem too because that's who I got my front brake kit from and here is their reply:

    "We have had no feedback concerning the brakes being too sensitive, Then again, our users seldom install 4 wheel disc brakes. The master cylinder specified has a 1" bore, which is correct for the application. Please review the plumbing to make sure it is routed correctly. You may try readjusting the PV; the car should nose dive a bit when the car comes the a "Stop sign" stop. Inspect the adjustment of the rear brakes.
    Did you adjust the push rod (really just a screw), that resides at the FRONT of the booster, to fit the master cylinder? There must be 0.01-0.03" of lash in this push rod."

    So what's the right way to measure the push rod lash? I'm thinking of using a veneered caliper's depth measuring end. Any other idea's out there??
  10. I'm running SN95 Cobra brakes on my '88. 13" 2-piston front brakes, rear single piston 12" brakes. Using a 1" bore MC. My calipers are smaller than yours however.

    KTga67, i'd love to help you here, but please take this advice with a grain of salt. I'm very experienced with brake retrofits on the Fox mustang, but it may not correlate on the classic stangs due to booster size, pedal geometry, please take this under advisement with what you decide to do.

    So here's a post i had written for Fox swaps a while back. If you read through it, you'll see where some of the math i'm about to do comes from. Basically what I am doing is taking known 1979+ Mustang caliper setups F&R and comparing them to known master cylinder sizes from same cars.

    The Ultimate 4-lug/5-lug Brake Conversion/upgrade Thread

    Digging around online, the Kelsey-Hayes front pistons are 41mm x 4 pistons, and the explorer setup is a single 48mm piston.

    That works out to a caliper piston surface area of:

    4-piston Kelsey-Hayes caliper (41mm piston x 4) = 10,552 mm^2 for both fronts combined
    Rear explorer caliper (48mm piston x 1) = 3616 mm^2 for both rears combined

    Thats 14,168 mm^2 of total slave cylinder area which is a LOT. If you see where i talk about ratios on that post, most of the factory setups from late models (with similar pedal geometry) are in the 13:1-17:1. Your current setup would be 27:1 with the 1" bore MC. Using the largest MC i list on that page, it gets you down to 22:1. Reducing power assist, or changing pedal geometry can change this however, which is why i say some of this may not correlate.

    Let me see if i can guess what your brakes feel like. The stroke is long, and in the beginning the brakes don't respond much. But, near the middle or bottom of the stroke, there will be a point where the brakes grab in an "all or nothing" sort of point. The actual distance from starting to grab to locking up will be short.

    I'm not sure i can personally recommend parts here as I don't have experience with the classic. But if anything i've said helps to educate you on making a good decision, then at least I can do that.
    #10 Mustang5L5, Oct 10, 2013
    Last edited: Oct 10, 2013
  11. I've measured the dept of the MC bore with calipers, then measure how far the plunger protudes and adjust it to 1/16 less than the MC depth. A check is to lift the front wheels and depress the brake a few times and check to make sure the front wheels aren't dragging.

    WHat you are doing with that adjustment is basically pre-loading the MC and taking any slack out of the pedal. You need to be careful here as preloading the MC by adjusting the lash outwards can cause the brakes to drag slightly.

    DOn't get your hopes up however, it won't affect sensitivity. You are taking up "dead stroke"