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Thread: Need Brake Help

  1. #41
    Senior Member karlos's Avatar
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    It does seem intuitive that air in the system would change the pressure reading, but that’s not actually the case. The volume of the trapped air will change as its compressed, but it will transmit pressure just the same as the fluid will. It may, however, limit the magnitude of the pressure that can be generated if the master cylinder were to stroke out before the column of air became fully compressed.

    Unless you have some idea of what readings to expect, the gauge readings are gonna be somewhat hard to interpret. This explains the value of the calculations, BTW. Not as a be-all, end-all, but as a way to gain insight into how the system works and what its sensitivities are. In the case of the system Dan’s running, i would expect to see a pressure ratio of 7:10, front vs. rear with the balance bar centered. This is based on the ratio of the areas of the two master cylinders (0.307/0.442 = 0.69, or approximately 70%). If you push on them with the same force (centered balance bar), then the pressures will follow that same ratio. If a ratio of 7:10 can’t be achieved with the balance bar in roughly a neutral position then something’s amiss.

    As a hypothetical, let’s say the measured pressures turn out to be 700 front and 800 rear (ratio = 7:8). This would mean the pressure in the rear circuit is lower than expected. If a reasonable adjustment on the balance bar doesn’t produce the expected result, then the gauge pressures indicate there’s a problem with the rears. Maybe the M/C ran out of stroke because it’s full of air, or maybe the seal is leaking backwards into the boot, etc.

    I think pressure gauges can be a useful, if limited, diagnostic tool. Taken by itself pressure doesn’t really mean much. And to get to what’s actually informative (ratio of front to rear) you really need to use two gauges simultaneously. I have a pair of gauges on the way. I’ll take some measurements and report back once I have something to look at. Particularly interested to see how close to center the balance bar actually is compared to where I originally set it, and in seeing the measured effect of adjusting the balance bar.
    Last edited by karlos; 12-03-2019 at 06:03 PM.
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  2. #42

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    Here is an update over the past few days.
    1. Pressure bleed all reservoirs to push all brake fluid out the four calibers.
    2. Removed the triple reservoir, removed front and rear master cylinders from the pedal assembly.
    3. Disassembled both master cylinders checked for problems, cleaned and reassembled.
    4. I had a new .75 inch master cylinder so replace the one I was using with the new one.
    5. Reinstalled both master cylinder and adjusted the balance bar according to forum and Wilwood directions.
    6. Check all fittings front to back for tightness or leaks.
    7. Bench bled both masters after installing back on the pedal assembly, pumped until no bubbles.
    8. Pressure bled the right rear then the left rear.
    9. Pressure bled the right front inside bleeder then the outside bleeder then the left.
    10. Pedal seems to be the same, soft. I may order a new .625 inch master.

    Dan







    7. Pressure bled the right rear then the left rear

  3. #43
    Senior Member Itchief's Avatar
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    Dan

    Just for s—-s and giggles try bleeding the passenger rear one more time and open the bleeder so that you get a good flow to the point you have used most of the reservoir and then test the brake pedal.

    For me getting the air out of the passenger rear line was a real pain.

    Just an idea you may want to consider

    Rick
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  4. #44
    Senior Member rich grsc's Avatar
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    I have no idea how a pressure gauge would give you any helpful info. The harder you push on the pedal, the higher the pressure would be. How are you going to be sure the same force is applied at the pedal each time you check a caliper? That and you have the mess of attaching and removing the gauge at each caliper, plus then introducing air into the system and re-bleeding the system AGAIN.

  5. #45
    Senior Member karlos's Avatar
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    The pressure gauge talk is a separate discussion going on inside the discussion. I'm sure it's all very confusing if you don't bother to read/understand the entire thread.
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  6. #46
    David aka Ducky2009 Ducky2009's Avatar
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    Dan,
    Here's a video from Wilwood. Important point, do you have two bleeders per wheel?
    https://www.google.com/search?q=how+..._s_QaQl6iYAw46

    As others mentioned, the balance bar setup is also very important.
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  7. #47
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    Here was my experience with a pressure gauge. My rear brakes worked very poorly. So I installed a pressure gauge and determined I was getting over 1000 PSI to the caliper(power brakes). The pedal was firm with no air in the system. Therefore I decided the problem was mechanical within the rear brake system and not the master cylinder. So, I replaced the mustang brakes with 4 piston Wilwoods and they work great, with the same operating psi.
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  8. #48
    Richard Oben's Avatar
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    Did you re locate the rears to be sure they are getting bled fully. See my other post about this on this thread. JMHO.
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  9. #49

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    Richard
    I looked at my rear Caliber, it seems my bleeder is almost at the 12:00 position or strait up. I have a picture on this post showing the rear. Did you have the same setup as I do? How important is it to level the Masters by lowering the rear of the car, I have read this a few times but thought bench bleeding the Masters on the car would take care of any air in the Masters.. my new 5/8 inch master comes today..
    Thanks Dan

  10. #50
    Richard Oben's Avatar
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    Looks like the same rear set up. We had a 3 link but it appears to be the same caliper. The bleeder pointing up may not get it bled, the air has to get to the bleeder. In the old days a LOT, I mean a whole LOT, of people put the fox front caliper on wrong and the the bleeder pointed up, which is logical, when it needed to point back. Because pointing the bleeder up the caliper was still half full of air. (there was a really good pic of this somewhere, could not find it) If the caliper is rotated either up or down the bleeder is at the top of the piston circle it will get the air out. We went through a lot of fluid trying but until we moved the caliper it was a no go. Right now the bleeder looks like about 10 o'clock on the piston circle not 12. JMHO. Richard.
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  11. #51

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    Just wanted to give you an update. I purchased two new Masters, .75 inch front .625 inch rear compact Wilwood masters. I bench bleed them off the car and again on the car. Dropped the rear if the Cobra so the masters were level in the car. Removed the rear calibers and milled out a pad size piece of aluminum the same thickness as the rear rotor, with the rears calibers removed i placed the spacer between the pads so I could rotate the calibers in any position so the bleeders are straight up. I pressure bled the system 4 times with no air bubbles coming out of the calibers. Pedal seem somewhat better but still not hard. I then had my wife help me pedal bleed, doing the front and rear rights side at the same time then the front and rear left side. Still no bubbles. I am going to replace all the Pads with Hawks “unless someone was better pads they can tell me” I am going to double check to make sure the Calibers are centered over the disks, I have read that can cause a soft pedal. Maybe the soft pedal is in my head and and I didn’t bed the brakes pads correctly when I first got it running. I attached a picture of a rear pad, it seems glazed what do you guys think? Also can any one tell me the part numbers for front and rear Hawk pads that fit my 12.88 6 piston fronts and 12.19 inch single piston rear? Would Hawks be the best pads? 1B0E345D-23D1-4BF6-86A6-1051D55A6EAE.jpgDC0A500D-0618-45E5-93C4-258531EB3E0F.jpg

  12. #52
    Senior Member karlos's Avatar
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    Some options, including Hawk, shown below. The BP-10s that come with the Wilwoods are pretty terrible. I'm currently running the choices shown in green, and find them to be a big improvement. Wilwood's website gives lots of additional info you can use to do some comparison shopping.

    Also, on the soft pedal: as measured at the pedal pad on the brake pedal, I see 1-1/4" of travel when pushing as hard as I can with my hand. May be useful as a point of comparison for determining whether or not it's in your head.

    Keep at it - you'll get it figured out.

    -Karl



    Last edited by karlos; 12-09-2019 at 01:40 PM.
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  13. #53
    Richard Oben's Avatar
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    Dan the bleeder being up is irrelevant. The piston circle has to be at the bleeder exit, not the bleeder up. It could be up, but it could be at 10. Like I said on the old mustang front calipers the bleeder pointed straight back, not up. JMHO R
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  14. #54
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    This thread has certainly covered all the bases regarding bleeding and brake line pressure generation, etc.

    So I thought I would offer a thought. Are you sure that the pads which shipped with the Wilwoods are street pads? If they are track pads, you will have much higher pedal pressure to stop effectively at the cold to moderate temperatures (relatively speaking) of street driving. Pad composition for street pads won’t hold up under track use and track-composition pads won’t perform effectively when cold. Ask me how I know......


    After all you have gone through, will be interested to see the effect of pad replacement, which I take from your last post you are considering.

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  15. #55

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    Karlos, i called the help desk with Hawk brakes he said the only brakes they have for the front calipers is the DTC-30 like you show on the above post. He told me the these brake pads will have way more stopping power than the BD-10 Wilwood pads that came from FFR, but will screech quite loud during braking and be dusty. I see the Wilwood pads you have on their website, are they loud and dusty during braking? Richard i will take a look at the rear calipers piston circle is up.

  16. #56
    Senior Member karlos's Avatar
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    No noise, a bit more brake dust. Most noticeable difference is that they actually stop the car.
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  17. #57
    Senior Member rich grsc's Avatar
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    Quote Originally Posted by DANW View Post
    Just wanted to give you an update. I purchased two new Masters, .75 inch front .625 inch rear compact Wilwood masters. I bench bleed them off the car and again on the car. Dropped the rear if the Cobra so the masters were level in the car. Removed the rear calibers and milled out a pad size piece of aluminum the same thickness as the rear rotor, with the rears calibers removed i placed the spacer between the pads so I could rotate the calibers in any position so the bleeders are straight up. I pressure bled the system 4 times with no air bubbles coming out of the calibers. Pedal seem somewhat better but still not hard. I then had my wife help me pedal bleed, doing the front and rear rights side at the same time then the front and rear left side. Still no bubbles. I am going to replace all the Pads with Hawks “unless someone was better pads they can tell me” I am going to double check to make sure the Calibers are centered over the disks, I have read that can cause a soft pedal. Maybe the soft pedal is in my head and and I didn’t bed the brakes pads correctly when I first got it running. I attached a picture of a rear pad, it seems glazed what do you guys think? Also can any one tell me the part numbers for front and rear Hawk pads that fit my 12.88 6 piston fronts and 12.19 inch single piston rear? Would Hawks be the best pads? 1B0E345D-23D1-4BF6-86A6-1051D55A6EAE.jpgDC0A500D-0618-45E5-93C4-258531EB3E0F.jpg
    Something doesn't look right with the wear on those pads. A pad should not set above the rotor, the pad should make 100% contact on the rotor. It looks like you have maybe a 1/4"(?) above the rotor?

  18. #58
    Member Inman Lanier's Avatar
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    On page 1, someone asked about glazed pads - no one picked up on that. My very first set of pads I changed when I was getting into autocross back in 1984 with my TurboGT Mustang - I cooked my set of new bendix pads following what I though were the 'bed-in' instructions. It turns out I applied way too much heat in the first stops and although not 'soft' in my opinion - the pedal was definitely not hard and created no brake torque. After going round and round, some buds and I determined I had cooked the brakes in my method of curing. I took them in, swapped them out for an identical set of pads, then did a much more gentle break in and they were fine.

    There are actually 2 things that need to happen with pads - they need to be cured (the glues and additives need to cook off), and the friction surfaces need to mate. The first part is potentially problematic based on method - the 2nd part takes care of itself with use.

    How did you 'bed in' your pads? The best way with new pads is to take the car up to 30 mph or so and do some 50% stops. You want to get them hot enough to where you just start to smell them off-gassing (that nasty brake smell when they get to temperature). When you smell them for the first time, stop braking at that point and let them cool (by driving around). Repeat this perhaps a half dozen times and you're done enough to where they will be fine (partially cured) and bed-in on their own going forward. The reality is that with pads and street driving you don't need to do anything at all! They will eventually get hot enough to off-gas, and the friction surfaces match the rotors with normal driving. Just recognize that early on, a panic stop on the highway with uncured brakes may actually fade them and you won't be able to stop as quickly. Generally, however you can get at least one decent stop on new pads before you overheat them.

    If you think you may have really worked some energy into the pads at bed-in - go get some cheap pads anywhere - put them in and see if it makes a difference.

  19. #59

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    Thanks for the advice on bedding the pads, I purchased a set of pads that Karlos suggested. I am checking to make sure the calipers are centered. I did read on the Wilwood instructions about adjusting the parking brake for the first time. It said to apply the brakes about 50% then cycle the parking brake a few times. I don’t remember doing that, wondering if this is some of my problem. It’s hard to do a test drive in MN it is going to be 12 below zero tomorrow.
    Dan

  20. #60
    Member Inman Lanier's Avatar
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    Not having applied the brake many times is NOT the problem (as I suggested most pads don't need any bedding considering the first panic stop caution). The only issue on 'bedding' is if you apply too much heat before they've properly cured.

    From many, many, many years both on the street and racing (autocross first, later road racing) - trust me the parking brake does NOT contribute in any way. You can ignore that recommendation.

    If you have the new pads in - did the pedal firm up? If no - it feels the same, then pads are NOT your issue.

    I've not heard it mentioned yet, but conventional rubber brake lines can have localize defect areas where they will balloon slightly w/o bursting. This is a small percentage of failures but from what you've been describing you're at a small percentage issue! Just keep that in the back of your mind now.

    Inman

  21. #61
    Senior Member rich grsc's Avatar
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    Quote Originally Posted by DANW View Post
    Thanks for the advice on bedding the pads, I purchased a set of pads that Karlos suggested. I am checking to make sure the calipers are centered. I did read on the Wilwood instructions about adjusting the parking brake for the first time. It said to apply the brakes about 50% then cycle the parking brake a few times. I don’t remember doing that, wondering if this is some of my problem. It’s hard to do a test drive in MN it is going to be 12 below zero tomorrow.
    Dan
    Yes the parking brake needs to be adjusted. If the P brake isn't adjusted correctly, the pads have to move a greater distance to the rotor, and the master cylinder runs out of movement and can't apply enough pressure at the pads. ALMOST all performance pads have break-in procedure, if yours lists one, follow it. A break-in allows the transfer of pad material to the rotor to increase friction, very important for certain types of brake material.

  22. #62
    Not a waxer Jeff Kleiner's Avatar
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    Quote Originally Posted by rich grsc View Post
    ...A break-in allows the transfer of pad material to the rotor to increase friction, very important for certain types of brake material.
    And speaking of the transfer of material...Dan, if you change pads it would be advisable to freshen up the rotors to eliminate any embedded material from the old pads. Minimally give them an aggressive clean up by using 40 or 60 grit on a DA or better yet by having them turned with just a couple thousandths taken off.

    Jeff

  23. #63

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    I did have the machine shop turn all four rotors just to be sure. I wanted to understand how the parking brake mechanics work so i took the puck out to look inside the caliper, by moving the parking brake lever on the caliper and watching the worm gear move inside the caliper was helpful for me to understand why wilwood’s directions say how to adjust the parking brake. Excited to see if this works. Jeff, i will buy you a cold beer and a steak if you come up here to MN and take it for a test drive, we are suppose to hit 10 above zero. Thank all for the help will keep you informed.

  24. #64

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    X-mas came early for me. I installed the new Pads today and checked everything over, I followed the directions on adjusting the parking brake and now the pedal is rock hard. It was a struggle but learned a great deal. Thanks all for your help, and Merry X-mas to you and all your families.
    Dan

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  26. #65
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    Dan,

    Great that you work it out. Still, check that the contact between the rear pad and the disk is right. Otherwise, the pad will wear wrong and might bring back the soft pedal.

    Quote Originally Posted by rich grsc View Post
    Something doesn't look right with the wear on those pads. A pad should not set above the rotor, the pad should make 100% contact on the rotor. It looks like you have maybe a 1/4"(?) above the rotor?

  27. #66
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    Dan,

    So in the final analysis what was the problem causing the soft pedal? Was it faulty or wrong sized MC's , the pads, or maladjusted parking brake?
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  28. #67

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    I think it was the parking brake. I installed the brakes and the original hand operated parking brake doing the build, then a few years into the build when i was designing the interior I decided to install the electric E-Stopp parking brake and must not have followed the final Wilwood instructions telling me after bleeding the brakes to apply 50% brake pedal pressure and cycle the parking brake a few time. Dan

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