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Discussion Starter #1
Hello everyone,

I recently did the Scarebird disc brake conversion with a dual master, the parts I used are followed:

1990 S10 Brake Calipers
1968 Mustang Rotors
Not sure on the rubber line
Willwood Prop valve (installed on the rear line)
1968 Galaxie Dual Master

I'm having very soft brakes, about 1/3 of the peddle has no action. I cannot even lock up the brakes.

Any suggestions, there is no air in the system and no leaks. I've looked everywhere. I'm going to order an adjustable pushrod to help get the peddle up some.

-Zig
 

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Hello everyone,

I recently did the Scarebird disc brake conversion with a dual master, the parts I used are followed:

1990 S10 Brake Calipers
1968 Mustang Rotors
Not sure on the rubber line
Willwood Prop valve (installed on the rear line)
1968 Galaxie Dual Master

I'm having very soft brakes, about 1/3 of the peddle has no action. I cannot even lock up the brakes.

Any suggestions, there is no air in the system and no leaks. I've looked everywhere. I'm going to order an adjustable pushrod to help get the peddle up some.

-Zig


Before you go nuts, I've been there, look over every fitting every part installed and the rest of the system checking for leaks etc.. The quality of parts sourced from the parts stores now days is low, I would look at fitting seal and the calipers. I installed SS calipers on a Corvette, new GM calipers, that were junk, I spent four hours trying to get the pedal hard using three different methods of bleeding the brakes before I noticed fluid weeping on the new pads.

So your master or the calipers could be defective, just because they're new doesn't mean much now days. Your master could be too small also.
Good luck:smile2:
 

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After my conversion my brakes would stop but it was just sort of a slowing down, nothing head snapping. I replaced the booster and now all is great. There are some checks you can try to see if the booster is working correctly, try them.
 

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Discussion Starter #4
Going to look at it piece by piece when I get back to town this weekend. I just don't feel like it's loosing any fluid...

Putt- its manual brakes, so no booster...
 

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make sure rear brakes are properly adjusted...
 

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Check all of the points in the previous posts. I did a four wheel conversion on my 66 Gal and had the same issue, spongy peddle. Checked all fittings, bleeding, checks for caliper leaks, etc. to no avail. The problem, in my case, was the distance between the brake peddle push rod and the master cylinder piston. The rod is adjustable in my car. the gap should be .020. When I did my conversion, I bought the master cylinder from MPBrakes and they provided the spec. on the distance. This link explains with a visual - Diagnosing and fixing a soft pedal | Booster pin to master cylinder gap | Master Power Brakes
 

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If you"ve still got your old master cylinder you could bleed it and put it back in. Kind of a pain because your new lines won't link up to it so you will have to kludge something together. If you old master did not have two ports maybe use just one port and see if there is any improvement. Basically you will be testing if your new dual is doing its job. It will also give you a second shot at bleeding the new master on the bench.
 

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Measure pressure at each wheel caliper, one at a time. You should have high pressure (look up the specs for how much) the same at all four corners. That will let you know if it is your pedal or another issue. Pressure gauges for brake lines are not to hateful in price. Put one in, have someone step on pedal with and without booster on to see what you get. Without booster, should be near manual brakes, with booster(car running), it should be much higher. Then record all four corners and you can tell what is going on. Air in lines, booster not working, lines clogged, misadjusted pads, etc.
 

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Discussion Starter #9
Before you go nuts, I've been there, look over every fitting every part installed and the rest of the system checking for leaks etc.. The quality of parts sourced from the parts stores now days is low, I would look at fitting seal and the calipers. I installed SS calipers on a Corvette, new GM calipers, that were junk, I spent four hours trying to get the pedal hard using three different methods of bleeding the brakes before I noticed fluid weeping on the new pads.

So your master or the calipers could be defective, just because they're new doesn't mean much now days. Your master could be too small also.
Good luck:smile2:
Looking like you might be the winner. Finally got back in the garage yesterday and pulled the "new" master. Bench bleed it again to find fluid coming out the back of it, wasnt much, but it also wasn't under any real pressure. I imagine with the lines on and pushing on the brakes it would be much more pressure and much more fluid. Picked up another one today and am hoping to install it tonight.

-Zig
 

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Discussion Starter #10 (Edited)
Haven't had the chance to drive it yet, however I got everything done yesterday and finally got a stiff petal, had a few small air leaks in my bleed nipples but it all appears to be ironed out, hope to take it for a spin today if the rain lets up when I get home.

Thanks for all the help and input!

-Zig
 
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