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Old 07-13-2013, 09:11 PM   #1 (permalink)
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Default Brake pedal pressure disc conversion

I completed a manual to power and drum to disc brake conversion on my 66. I used spindles, rotors and calipers from a 71 mustang along with the 71 proportioning valve . I bought the SSBC booster kit with master cylinder. I've bench bled the master cylinder twice. Bled all the lines several times and am not getting any air. My problem is brake pedal pressure. It's weak. The pedal also travels about 1/3 before the brakes start to grab. And when it does as I said the pedal pressure is weak. I've adjusted the adjustable brake pedal rod and it doesn't help. Calipers, pads, lines, rotors, master cylinder and booster are all new parts. Do I have a bad master cylinder? Anyone have any thoughts or suggestions?
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Old 07-13-2013, 09:20 PM   #2 (permalink)
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1. If you installed a used brake safety valve it might be switched to one side and need recentering. It can be off center and still bleed at all 4 wheels. Does the lite switch show it to be centered.

2. I don't know your particular kit but I often have to change the location of the brake pin on the pedal to reduce pedal travel and mushyness when adding a power booster.

kind of a nightmare for one that hasn't done it imo.

Last edited by barnett468; 07-14-2013 at 09:12 AM.
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Old 07-13-2013, 09:29 PM   #3 (permalink)
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1. I did use the used proportioning valve from my 71 parts car. I don't have the light hooked up but can check that.
2. I was told by SSBC if I have the adjustable rod adjusted too far it will cause the brakes to drag. That seem right? Move the pin closer to the firewall?
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Old 07-13-2013, 09:38 PM   #4 (permalink)
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Quote:
Originally Posted by bluemustang66 View Post
1. I did use the used proportioning valve from my 71 parts car. I don't have the light hooked up but can check that.
2. I was told by SSBC if I have the adjustable rod adjusted too far it will cause the brakes to drag. That seem right? Move the pin closer to the firewall?
Yes ssbc is correct good info from him.

Move pin 1/2" lower if necessary, and possibly front or rearward. Wait until system is working to see if it is necessary. it's a job.

Last edited by barnett468; 07-14-2013 at 08:51 AM. Reason: clarification
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Old 07-13-2013, 09:49 PM   #5 (permalink)
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Thats what they said. I'm not sure if I understand freeplay. The pedal has to move 1/2" before pressing the rod into the booster/master cylinder?
We I've already fabricated a trans mount for the FMX I stuck in the car I might as well fabricate the brake pedal too.
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Old 07-13-2013, 09:54 PM   #6 (permalink)
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Thats what they said. I'm not sure if I understand freeplay. The pedal has to move 1/2" before pressing the rod into the booster/master cylinder?
We I've already fabricated a trans mount for the FMX I stuck in the car I might as well fabricate the brake pedal too.

The clearance between the rod and the mc piston should be provided by the mfg of the kit, if it is not then call them for a spec. If they do not provide one then try from 0 - 1/16".

Last edited by barnett468; 07-14-2013 at 08:54 AM. Reason: clarification thanks to ssbc
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Old 07-13-2013, 10:19 PM   #7 (permalink)
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Default pedal freeplay

Can you help me understand what you mean by pedal freeplay? I thinking it means the pedal will bounce around because there is no tension on it.. but I'm not thinking that is right now..
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Old 07-13-2013, 10:36 PM   #8 (permalink)
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Can you help me understand what you mean by pedal freeplay? I thinking it means the pedal will bounce around because there is no tension on it.. but I'm not thinking that is right now..
Does your rod lock into the master?

Does your pedal have an upper stop?

The pedal can not DEPRESS the piston at all when your foot is not on it.

Last edited by barnett468; 07-14-2013 at 08:56 AM. Reason: clarification
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Old 07-14-2013, 07:12 AM   #9 (permalink)
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The rod does not "lock" in the master cylinder. I could loosen it all the way under the dash and take it out if I need to. The rod is adjustable and there is a fine adjustment on the booster where it pushes the master cylinder piston.
The pedal does have an upper stop. The pedal and mounting assembly for the pedal are all stock 66.
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Old 07-14-2013, 07:41 AM   #10 (permalink)
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Quote:
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If you put the rod at 0-1/8" freeplay it should be fine.
If he's talking about headspace, Ford spec is 0-0.012". 1/8" would be WAY too much.

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Old 07-14-2013, 08:25 AM   #11 (permalink)
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I used the method SSBC suggested to get the space between master cylinder and booster. I stuck a chunk of clay in between and got about a credit card thickness smush when the master cylinder was mounted to the booster. (I pulled off the master cylinder to check it after mounted)
The pedal push rod is also adjustable but there wasnt much instruction on adjusting that. Other than about 1/2" freeplay.

Just thinking out loud if I add a spacer of some kind to the factory pedal stop, that will decrease the travel of the pedal. That would help eliminate some of the problem?

Last edited by bluemustang66; 07-14-2013 at 08:28 AM.
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Old 07-14-2013, 09:10 AM   #12 (permalink)
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Quote:
Originally Posted by bluemustang66 View Post
I used the method SSBC suggested to get the space between master cylinder and booster.
Yes I'm glad he clarified that, my post sucked, I corrected them. The mfg of the kit should have provided that spec though.




Quote:
Originally Posted by bluemustang66 View Post
I stuck a chunk of clay in between and got about a credit card thickness smush when the master cylinder was mounted to the booster. (I pulled off the master cylinder to check it after mounted)
Ingenious



Quote:
Originally Posted by bluemustang66 View Post
The pedal push rod is also adjustable but there wasnt much instruction on adjusting that. Other than about 1/2" freeplay. Just thinking out loud if I add a spacer of some kind to the factory pedal stop, that will decrease the travel of the pedal. That would help eliminate some of the problem?

Ok, hope I don't screw this one up, lol. I would do this. Adjust rod so it pushes the pedal towards the stop until it almost touches it. Then check freeplay on pedal. I should be around 1/2".

If your pedal travels a very short distance to stop the car and you want to lower the height then readjust rod lowering pedal to desired position and place spacer on pedal or stop to prevent it from having so musch freeplay that rod could fall out if you lifted up on pedal.

Don't lower pedal yto the point that when it is fully depressed your foot can hit the gas pedal, lol. Saw this happen once.

Don't worry about porportioning valve. I meant to say brake safety valve. This is the one with the lite switch. If you used an old one than check to see if it is centered or switched to one side from a previous brake leak.

Last edited by barnett468; 07-14-2013 at 09:14 AM.
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Old 07-15-2013, 08:30 PM   #13 (permalink)
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ok I've been messing around with the pedal and adjustable rod. I think I have it too tight to the stop because my brakes are dragging. Would that cause that problem?
Also the pedal travel is still too long to stop the car. My 71 Mustang which is stock, I just set my foot on the brake pedal and it stops the car. The way this 66 is now I have to almost have the pedal to the floor before it full stops the car.
I'm not having any luck.
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Old 07-15-2013, 08:40 PM   #14 (permalink)
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Quote:
Originally Posted by bluemustang66 View Post
ok I've been messing around with the pedal and adjustable rod. I think I have it too tight to the stop because my brakes are dragging. Would that cause that problem?
I already answered this in my previous post. Yes it might cause brakes to drag. Some other causes are rod to mc piston is adjusted too tight putting pressure on piston. Residual valve holding too much pressure if you installed one.





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Also the pedal travel is still too long to stop the car. My 71 Mustang which is stock, I just set my foot on the brake pedal and it stops the car. The way this 66 is now I have to almost have the pedal to the floor before it full stops the car.I'm not having any luck.
I mentioned you would likely have this problem and told you one way that I fix it.
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Old 07-15-2013, 09:01 PM   #15 (permalink)
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I had a similar issue and ended up having air in my lines..in spite of numerous bleedings. I installed 'speed bleeders', fixed. Somehow I was pulling in air around the bleeder threads. I understand this can also be fixed by putting grease on the bleeder threads if you don't have the speed deals with the check valve.
Good Luck!
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