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Discussion Starter #1
I am converting a 74 nova from front drum to disc, I bought a master cly and prop valve from classic performance, and factory nova rotors mounts etc, reman calipers from autozone new caliper hoses also. I bench bleed the master then bleed the system and I have no brake pedal, just goes to the floor. If I pinch the three rubber lines I have a solid pedal, if I remove the clamp off the rear line still have a solid pedal, but when I remove the clamp off of both or either front line the brake pedal goes to the floor, so then I took the calipers off the mounts and put a c clamp on and pushed the pistons all the way in and left the clamps on, the pedal still goes to the floor, with e clamps still on and I pinch the front lines, solid pedal. I have no leaks calipers and mounted correctly with the bleeder screw on the top. Any Ideas????? my guess is bad calipers from autozone, but to get two bad ones at the same times, the odds have to be high.
 

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1970 Nova SS 350 Brandon, MS
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It sounds like you isolated the problem to the calipers but haven't confirmed the caliper is the problem. If you clamp the calipers fully compressed and still no pedal, why would that cause the caliper to be bad? At that point, the caliper is just a big, heavy plug or cap at the end of the hose. I think you still have a huge air bubble in the caliper.
 

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Discussion Starter #3
I agree that is a possibility I am using a pneumatic vacuum bleeder, could that be the problem? when I hook the tube up from the bleeder to the bleeder screw on the calipers I get a solid stream of fluid. If there is a huge bubble of air in the calipers how would I go about getting it out?
 

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1970 Nova SS 350 Brandon, MS
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Another thought...which master cylinder do you have? There are dramatic differences between the disc/drum (F/R) and drum/drum masters. If you have one for drum/drum it will not have the capacity to properly operate the disc calipers. I fought this when I converted my CJ7 from rear drum to rear disc.
 

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Discussion Starter #5
I bought a master cylinder and prop valve from Classic Performance Products for disc drum setup and I have checked with them to make sure I have the correct setup. Any ideas as to how to get the air bubble out of my calipers? I am working alone which is why I am using a pneumatic vacuum bleeder. I'm getting a solid flow of fluid in the clear hose on the bleeder.
 

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I have a pneumatic vacuum bleeder and have found that they work well to initially fill an all new system with fluid but really do not get all the air.
I've more successfully used a Phoenix Injector. They actually force new fluid thru the system. You can either inject the fluid down thru the small hole on the MC reservoir (this really works well and eliminates the need for bench bleeding the MC) or, so called reverse bleeding by injecting the fluid thru the caliper bleeders. Either way, all the air is pushed out.
 

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Discussion Starter #8
I got my phoenix bleeder, bled the system and no improvement. I even took the calipers back and exchanged them, bled the system, no improvement. If I pump the pedal like crazy I get maybe a 1/4 pedal but really spongy, let it sit for 30 seconds and it goes to the floor again. If I knew it was going to be this big of a pain I would have left it drum brakes.
 

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Discussion Starter #10
Im starting to think your right. I called CPP and they swear up and down I have the right m/c prop valve. but I don't know what else it could be. I know there is NO air in my lines. im considering buying another m/c prop valve from someone else and tossing the CPP stuff in the garbage.
 

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I swapped my 62 from drum/dum to drum/disc, using a CPP master & prop with 68 Nova discs brakes with good results and below average skills. Trust me it's worth the headache. I agree with the comments above sounds like you're on the right track.

A couple of things that came to mind reading your post were:

A) I had to shorten the length of the push rod in my case. Maybe that needs adjustment?

B). Are the pads able to grab the rotor? From the description it sounds like everything is working other than that, unless I'm missing something.
 

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Discussion Starter #13
I have about 3/8 In of play in the brake pedal itself before the rod hits the piston, so I don't think that needs adjustment. It was like that with the four wheel drums. I have not checked if the calipers are grabbing the rotors. I personally think its not moving enough fluid to the calipers, bypassing somewhere, the guy at CPP said that's not true cause pinching the line gives me a pedal, but to me all pinching the line proves is that fluid is moving,doesn't prove that enough fluid is moving.
 

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Whip, have you tried to adjust-out the 3/8" of free movement you say you have between the pedal rod and the MC piston? I generally bottom out the rod in the piston w/o adding any preload.
As you mentioned, you may not be pushing enough fluid to the calipers
 

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1970 Nova SS 350 Brandon, MS
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I have about 3/8 In of play in the brake pedal itself before the rod hits the piston, so I don't think that needs adjustment.
You may have found the 'smoking gun'. That 3/8" may be the reason you are not getting enough fluid. As already stated, adjust the free play out (but don't preload) and see what happens.

One other thought, are your pads (all 4) almost touching the rotors (both) with no pressure applied? If they have a big gap when relaxed, you may be using all of your pedal stroke just getting the pads to the rotor with nothing left to clamp down. The pads (inner and outer) of each caliper, when relaxed, should have 'slight' drag on each rotor. I cannot remember what causes the piston to stay in the properly 'adjusted' or 'extended' position once pressure is relieved but if the pistons fully retract and create a gap between the pad and rotor there may be a problem.

About the calipers, do they have the freedom to move side-side on the mount bolts/bushings? Not completely loose on the bolts but maybe with a little drag that is caused by the O-rings that the bolts/bushings must pass through.
 

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Discussion Starter #18
when I say 3/8 I mean actual pedal travel at the pedal not the rod, not sure what the ratio is but the rod is moving maybe 1/8 before it hits the piston. It had the same free play with the old m/c with the drum brakes. That still doesn't explain why it goes to the floor and why when I pump it like crazy and only get a spongy quarter pedal 30 seconds later it goes to the floor again. the pads are touching the rotors, no gap and when I pump it and hold the pedal if I put a bar in the wheel studs I can rotate the rotor.
 

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1970 Nova SS 350 Brandon, MS
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This is definitely a weird one...have you tried pinching the front hoses and leaving the rear hose un-pinched? I wonder what that will do to the pedal?
 
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