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Discussion Starter · #1 ·
Vital info is: 1967 mustang with 289 (mildly built) and automatic trans. Replaced the front drums with 77 Granada and the master cylinder with a 77 mustang power unit. I added a proportioning valve into the rear brake line. I have adjusted the rear brakes and bled the whole system several times. (by the way, all brake lines have been replaced, the rear brakes complete rebuilt as was the fronts, new rotors reman calipers, etc. sparing no change) The problem is I can tell that the vacuum assist is working and the pedal will move a little over 1 1/2 " (at the pedal not the plunger rod) then I get the actual hard pedal and can pressure up enough push for about another 1" of pedal travel. The car will start to come to a stop but does not nose dive and the wheels lock. No matter how hard I push the pedal it will only slowly come to a stop. Got any ideas? Also I've adjusted the proportioning valve either way with the same results and I have bench bled the cylinder twice. help please.
 

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Drop the proportioning valve if you wan't the brakes to squeal.... How "soon" do you stop? What is the distances in your 40 mph to 0 stopping distance wise... And 55 mph to 0, and 25 mph top 0.???


FE
 

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Discussion Starter · #3 ·
Actually this all started before I installed the proportioning valve. Adding it didn't change a thing nor does adjusting it. I have not taken it out of the driveway cause no matter how hard I press on the pedal it will not stop quickly and I don't want to end up in someones livingroom. It's like the brake pedal has hit the floor before it's had a chance to complete the needed pressure (but it's not hitting the floor) and with the master cylinder off, the pedal will hit the floor (with ease) and it will push the push rod out of the booster about an inch which seems to be the stroke distance on the master cylinder.
 

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Discussion Starter · #4 ·
All, I have ordered another master cylinder to see if there is a problem with the first one that came with the powerbooster. Also removed the calipers and greased the caliper slides, etc. I didn't think about it until I went back together but I understand that the caliper pistons could be seized. (note: I understand this could be true on existing calipers), but these are remans, should that happen? They've been on the car for about four months before we got the car running. Could moisture gotten inside and formed rust? I get some pressure to the front disc but now enough to really stop it.
 

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Kinked or blocked brake line?

Have you bled the brakes, is sufficient fluid coming out?

The only way for the calipers to rust internally is if you had the line fitting or bleeder screws open (minus the plastic caps or other fitting to keep water out) and in the rain. It's not likely just having the plastic caps off would make them rust without some water.

Are you running a master cylinder proportioned for Disc/drum brakes, or is it a strictly drum brake cylinder? Drum brake cylinders can't generate the necessary pressure for a disc brake system, and you'll have the symptoms you described, no matter how much you choke off the back brakes.
 

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Lift the front wheels off the ground and spin them and put the brakes on. They should stop suddenly. You probably don't have a big enough piston in the master cylinder. Disc brakes require a bigger psiton size and you might also check to see how much play you have in your MC rod-PB diaphram.
 

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Get a brake line pressure tester, SSB has them.Anything under 800# and you have a problem. I like to see at least 11-12 hundred PSI.
Don't go to big on the M/S bore, 15/16"--7/8" is what you should try for.
Don' t get rid of the propo valve, unless you want to swap ends in a panic stop.
 

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Discussion Starter · #8 ·
The calipers were installed on the car and the car has been in my garage (dry) for about four months during body work and paint, engine build, etc. with the seal plug in. They shouldn’t have any moisture in them. During each brake bleed all lines were open and fluid flowing without any restriction. All lines are new, no kinks. I have raised the car and spun each wheel and each come to a stop and I cannot move them by hand. The power booster and matched master cylinder is for a 1977 mustang and is disc brake only if I’m correct, so it should be strong enough to handle the job, but I’m not sure what bore size it is. The booster to master cylinder rod should have been set correctly at the factory and we have tried changing it but that didn’t help and we set it back to where it was set with very little room when the pedal is open, not depressed. The proportioning valve we bought from Summit (SUM-G3905), but this was installed to try to solve this problem.

<font size=-1>[ This Message was edited by: my67mustake on 9/6/06 3:01am ]</font>

<font size=-1>[ This Message was edited by: my67mustake on 9/6/06 3:02am ]</font>
 

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Discussion Starter · #9 ·
All, I bench bleed the "new" master cylinder (took quite a while to get all of the air out) and installed the new cylinder. Guess what ... same thing, no hard pedal, but I haven't bled the complete system yet. I think I'll pull the calipers at this time and push them back a bit to see if they needed breaking loose then bleed the system. ... Later.
 

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Discussion Starter · #10 ·
Ok, calipers are ok easy movement, bled the front brakes for now. I'm looking at the brake pedal to powerbooster rod hookup and it seems the rod maybe too short. later ...
 

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Discussion Starter · #11 ·
Got'er dun ... the booster push rod being different in length and slightly off set from the original push rod was binding. I relocated the pin on the pedal that the rod goes on and now we have brakes. I'll finish bleeding the rear brakes.
 

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You may run into a problem where the break lights won't shut off, if the angle is not set up correctly.

There is a little rubber pedel return stopper up inside the dashboard. Shave it down a little if you have this issue.
 

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Discussion Starter · #15 ·
The brakes work great now I just have to make it go. See "transmission rebuild". This car must be cursed! As far as the brake light switch problem it's just the opposite. I can move the pedal in about an inch and a half before I get to the actual braking pressure and the brake lights come on at that time. (power brake unit)
 
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