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Classic Mustangs Tech Forum

Technical discussions specific to 1964-1967, 1968-1970, and 1971-1973 Classic Mustang. Discuss all tech related to in-line six cylinder and V8 powered Vintage Mustangs here.

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Unread 04-19-2008   #1 (permalink)
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Default 1968 Mustang Brake problems

I have a 1968 Mustang with the drivetrain and braking system out of a 1970 cougar. The car has rear drum front disk power brakes. Ive already put a new Master cylinder, for the cougar setup, on the car. It was originally a 200 I6. My problem is the brake pedal had no resistance until you press it in 3 or 4 inches,at which point it rock hard. Within that 3 to 4 inches is your braking, which if way too touchy. I believe the front brakes are applying too much. It still has the original distribution block which is probably not a good idea. Would there be a way to correct this with an adjust proportioning valve if that were the case.

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Unread 04-19-2008   #2 (permalink)
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welcome to the site,enjoy!!!! are the rear brakes adjusted right?are you getting good pressure to the rear brakes?
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Unread 04-19-2008   #3 (permalink)
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yeah I pulled the drums. The shoes are adjusted out. Cant turn them with car in air and brake applied.
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Unread 04-19-2008   #4 (permalink)
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sounds like all is working right,you may need to change the valve if you want more pressure at the rear brakes.most disc and drum systems are 70% front and 30% rear stopping power.
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Unread 04-19-2008   #5 (permalink)
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Hello. It sounds like you might actually have a couple of problems. The brakes that you have in the car now should have a proportioning valve for the rear brakes and a check valve for the front discs. The rear brakes aren't hitting soon enough and the fronts are hitting too hard. If the check valve is bad, that would account for the front, and the proportioning valve would account for the rear. Unfortunately, neither are adjustable on the original system. I'm pretty sure that the 69 Cougars used the same master cylinder push rod as the 69/70 Mustangs, so that isn't going to be part of the problem. Replacing the check valve and proportioning valve with adjustable units should straighten you right out. Hope that helps.
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Unread 04-19-2008   #6 (permalink)
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Are you referring to the distribution block?
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Unread 04-19-2008   #7 (permalink)
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Quote:
Originally Posted by daysvilleman View Post
Are you referring to the distribution block?
Hi again. Nope. Based on the way that you've probably never even heard the term ' Check Valve' before, I'm guessing that yours got lost in the shuffle somehow. Your system should have a distribution block, a proportioning valve and a check valve. The purpose of the check valve is to keep the brakes from doing what it sounds like your brakes are doing. The proportioning valve balances out the force that's applied to the front and back. The check valve makes them hit at the same time. If you imagine two people holding a rope and one of the people gives the rope a flip, you will see a wave travel down the rope. If you imagine two pairs of people holding ropes with one rope being twice as long as the other, and they give both ropes a flip at the same time, the wave will hit the other end of the short rope first. That's what your brakes are doing. The check valve is there on the front brakes to slow down the wave in the short rope enough to make sure that both waves start AND finish at the same time.
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Unread 04-19-2008   #8 (permalink)
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I did try to use one of those adjustable proportioning valves . I installed it between the master cylinder and the distribution block and it made no difference. As far as i know their are no valves between the distribution block and the the brakes themselves. I will double check that though. The car was original set up with manual 4 wheel drum.

Thank you very much
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Unread 04-19-2008   #9 (permalink)
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Hi again. What the Cougar would have had originally would be the same thing as a 69/70 Shelby. That's the set-up that you want in your car. Knowing that might help you out on finding parts, diagrams, etc... I should have the diagrams and part numbers stuck away somewhere. I'll see if I can find that stuff.
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Unread 05-11-2008   #10 (permalink)
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Do your rear wheels lock up during hard braking?
I just did the Scarebird disc swap for the front and I haven't swapped the m/c for a disc/drum
Its sounds to me like Veronica is right, but you need to make sure your M/C is for disc/drum, one of the resevoirs should be bigger than the other one
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Unread 05-12-2008   #11 (permalink)
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You won't have any check valve to locate because you have the dual braking system. It's in the M/C. You must have the correct M/C for the disc/drum system, though. You also have the adjustable proportioning valve installed wrong. The P/V is plumbed into the rear brake system after the distribution block. It should not be connected into the front system at all. If you have the original P/V it will be located just before the flex hose for the rear brakes. Don't have but one of these in the system, the original or the adjustable type, but not both. If the brake lines that are on the car was for an all drum system there won't be a proportioning valve in the system.

As for the pedal travel, you may need to adjust the pushrod that is between the master cyl. and the brake booster and make sure that the vacuum line's check valve at the booster's vac. inlet is working.
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Unread 05-13-2008   #12 (permalink)
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You say you're using the original distribution block. Did you do anything to it? Check out http://i245.photobucket.com/albums/g...rakeDistV1.jpg

The block should now only split flow to the front brakes. The front port is plugged. The line to the rears goes from the MC to the Proportioning valve.
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Unread 05-15-2008   #13 (permalink)
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Alright i changed out the Distribution block to the Proper block out of a 1970 w/ power disc. This seemed to eliminate the hard stops, but the pedal still had little resistance. Found that the Brake booster was giving me no boost. Replaced it with a remanufactured one and upon installation found that the Master cylinder Push rod was too long. I tried adjusting it to its shortest length and its still about an inch too long before i can get the M/C properly mounted on the booster. Any suggestions on how to handle this. Im hoping this is my last hurdle to get some good brakes.
THanks
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Unread 05-16-2008   #14 (permalink)
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Sounds to me that you have the wrong booster or master cyl. There shouldn't be anything that is that far off.
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Unread 05-19-2008   #15 (permalink)
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Well it was the wrong Booster. Turns out the booster that was originally in the cougar parts car was out of a 1970 Mustang.It still doesnt make any sense because the master cylinder i have is listed to fit both a 1970 Mustang and a 1970 cougar, so i would think that both boosters should bolt up to the same m/c with no issue. Anyways i now have it installed but the brakes are still screwed up. The pedal has such so Little resistance when you push it that the spring will not surpress enough in the brake light switch to turn them on. Its almost like their is too much power booster if that is possible. Im getting pretty good braking. When the brakes apply you dont feel it in the pedal though, You need to float the pedal in that "sweet spot" to gradually stop. I am at wits end here. Anyone that has possibly heard of such a thing it could use advice.

One more note is when you press the brake all the way down and let it off the engine studders for just a second.

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