Brake problems continue - Ford Mustang Forum
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post #1 of 11 (permalink) Old 4 Weeks Ago Thread Starter
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Brake problems continue

Regular readers of this forum may recall my thread awhile back about problems with a power brake install in my '66 (289, C4): excessive pedal travel.

I took a break from that for awhile, no pun intended, but am working on it again. I first removed the power brake kit and replaced it with a Leeds Brake manual m/c and push rod mentioned either on this forum or the VMF. I did this to try and simplify things, and I do like that I how have room to work on things.

I also replaced the 30-year-old SSBC front disk brakes with a Wilwood kit.

I adjusted the push rod so that the pedal was as high as I felt it could be and still be usable. I also had to rework the lines at the m/c to match the new unit. I bled all four wheels in the proper order, almost a pint of fluid. No leaks; I checked several times. The pedal still goes all the way to the floor. It doesn't feel spongy; I feel resistance all the way to the floor, and it comes back slowly when I take my foot off. The instructions that came with the Wilwood kit say that this can be caused by the m/c capacity being too small.

I blocked the pedal to the floor and checked the front wheel rotation. No resistance from the brakes.

I next removed the front line from the m/c (rear brakes) and plugged the port. The pedal still went to the floor. I removed the rear line and plugged that port (front port still plugged). I got a hard pedal with very little pedal movement. I'm guessing that means my bench bleeding of the m/c was successful.

One other possible significant observation: I did all this with the proportioning valve set to max pressure to the rear brakes, figuring that would ensure getting all the air out during bleeding. When I changed it to minimum pressure, the front wheel brakes began to work a little (the wheels were harder to turn).

I'm now thinking this may point to needing a larger m/c. The Leeds unit has a 1" bore, as did the one on the power brake kit, which might explain why I had the same issue with it. I've found a Wilwood m/c with a 1.125" bore, but would appreciate any advice before spending the money yet again.

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post #2 of 11 (permalink) Old 4 Weeks Ago
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FWIW a few months ago, I was setting up a dyno fixture with a brake setup (I work in prototype vehicle testing), and I couldn't get the brakes to work properly. Checked the setup several times, and even found that it did work with only 1 side (out of 2) hooked up. We did come to the determination that the master cylinder bore was indeed too small. You'd be surprised the difference that 1/8" bore size makes when it comes to moving fluid (I was). With that being said, I'm thinking you're on the right track.

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post #3 of 11 (permalink) Old 4 Weeks Ago
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Hi Charles, ok, IMHO, to me it sounds like 1) defective pressure valve and 2) unmatched or defective master brake system. IMHO, your "kit supplier" should be able to supply you with the "Specific Hydraulic Specs" for the system as a whole and the individual brake components. If they can't or won't, run don't walk away because they have done no engineering on a critical safety system...merely going by general swag component comparison...Ö SWAG is ok for those working in their backyards (with trial & error testing), but for a company selling and making $'s, this is, well, you know.....there is a legal word for it.


I would go back to what has been successfully used for 30+ years prior...Ö go purchase a 1974 V8 Ford Maverick master brake cylinder....they come in power, non-power, drum/drum and disc/drum versions (and if you do a little R&D, there are actually successful applications using this with disc/disc). You will now have a MBC that is specifically designed for the size, weight, power, braking systems of that car..... my swag is you will at least have a system that is functioning..... will the hydraulic volume be enough? Only your component mfg will know....if they won't help, get rid of their components as well, replacing with oem spec components and upgraded brake linings (CE of .49 or +)..... this should put you in about the same performance range as most of these aftermarket systems...Ö. remember, the aftermarket systems cannot (regardless of the PR) give you race car like braking on the street...for two reasons....1) the system will override the cars ability to stop....meaning it's functioning at a far greater efficiency than the tires, suspension, etc. is designed to function at...so guess what...actual stopping capability is no greater in most cases than a properly setup system and 2) If they really did give you a race car type capability...you are now at risk of stopping faster than most anyone else...meaning you are now at risk and so are others on the road.....there is a "performance range" that is considered "acceptable"...and yes, a 911 can out stop a Kia but when you look carefully at the full spectrum, if the drivers are paying attention, each has the ability of stopping before hitting each other (too severely).

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post #4 of 11 (permalink) Old 4 Weeks Ago
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Charles, are you sure that the ports on the MC aren't feeding the right brakes?
Meaning that the front line is screwed into the rear brake socket or vice versa.

I am finding it a bit hard to believe that the MC ports are too small and that after holding the pedal down that your front wheels are still spinning. Surely there would be some braking action, not nothing at all.
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post #5 of 11 (permalink) Old 4 Weeks Ago Thread Starter
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I am positive the rear disc brakes are connected to the front (small) and the front brakes to the rear (large) bowl.

I guess it's possible the proportional valve is at least part of the issue. It's the only thing left from the power brake setup I ditched. It is an SSBC valve I've had for awhile. I don't think I tried spinning the front wheels with the rear brake port plugged. I will try replacing the proportional valve with Wilwood's unit.

As far as using matching components, both front and rear brakes are Wilwood, the ones they sell for the '66 Mustang. Getting everything from one manufacturer is one reason I'm considering getting a Wilwood m/c, although Summit says the Leed m/c works with disc/disc on a '66 Mustang.
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post #6 of 11 (permalink) Old 4 Weeks Ago Thread Starter
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Looks like this might do the trick; at least it's all from one manufacturer:

https://wilwood.com/MasterCylinders/...o=261-13270-BK
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post #7 of 11 (permalink) Old 4 Weeks Ago
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I also bought the SSBC front disc conversion kit (including MC) for my 66. While they work OK in normal driving, semi hard braking has the pedal almost on the floor. I only drive it (carefully) occasionally to local car shows. Sounds like the same issue you have, so I'll be following this thread looking for an answer.

Keep up, or move over!
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post #8 of 11 (permalink) Old 4 Weeks Ago Thread Starter
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One of the reasons I got rid of the SSBC front brakes is because they just closed up shop. I was worried about getting repair parts in the future, but have since learned that at least mine are Kesley-Hayes calipers. Parts are available.

But I never had any problems with them. Mine only started after I installed a power brake kit.
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post #9 of 11 (permalink) Old 2 Weeks Ago
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I was told to use a dual diaphragm booster. I was also told to use a mc that has at least a 1Ē bore. I have a single diaphragm booster from the front disc conversion that I installed. I bought it from Kentucky Mustang. They told me the mc was a 1Ē bore. While the brakes work fine, they just donít feel like they actually apply until after a fair amount of travel is applied to the pedal and there is no resistance to the pedal during that travel. Iíve driven 66 stangs before that have ďbig toe quality brakingĒ meaning you can feel the brakes applying immediately with just your big toe on the pedal. Since my brakes work fine Iím not in a hurry to improve them but I suspect that the booster might be inferior to the ďgoodĒ quality braking feel. Just guessing
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post #10 of 11 (permalink) Old 2 Weeks Ago
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This is the system that I installed. https://www.kentuckymustang.com/Disc...-66-p/5961.htm
I know you said that you bled the system but it sounds like youíre not moving any fluid if the pedal goes to the floor and brakes donít apply? Yet when you plugged both out ports the pedal doesnít move should mean the mc is working? I agree with beechkid. Sounds like there may be a bad check valve in the mc causing fluid to only move internally in the mc instead of out through the lines?
Keep plugging. Youíll figure it out.
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post #11 of 11 (permalink) Old 2 Weeks Ago Thread Starter
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Thanks for the responses, Tlkmap. The Leeds Brake m/c is new, so it's hard to believe it might have a problem, especially when I had the same problem with the previous m/c.

I'm in the process of installing the 1-1/8" bore Wilwood m/c with their proportioning valve, a really nice setup; will report on how that goes.

One thing its instructions mention is that the brake pedal should not hit the floor before the m/c hits the end of its travel. It's in the car with no fluid in it yet while I fab lines, but the pedal did hit the floor. I had lengthened the push rod as far as it would allow, so I got a Wilwood pushrod kit. Tried that yesterday, but no help. By the time I shortened it enough to get it on the pedal (the pedal was all the way back, hitting the upper bumper), the pedal still hit the floor.
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