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67 Camaro, new 4 piston disc brakes up front, new lines, new 70 vette power mc, new hoses, hydroboost in the manual hole, rebuilt 79 seville rear with disc, new rear hose, new rear lines...I removed the original distribution block and used a three way female flare union block for the fronts and plumbed in a wilwood proportioning valve for the rears.

I've bled the system several times, there is no air. I've bench bled the mc (I have two new mc's, tried them both) until the piston can only be pushed in 1/8 or so (plugged the mc ports to bleed). I've also bled the mc using the hose method...there is no air. I've checked every connection (about 25 times each), there are no leaks. I have bled everything using my mytivac until there is no air, I have gravity bled the system and I have had a helper pump up the pedal and cracked the bleeders...no air. I have had a helper pump up the pedal and I cracked the mc connections and others for that matter with no air.

Seville brakes are funny...you ratchet the parking brake lever to get them adjust right. They are set correctly with about one inch of movement on the parking brake lever before they lock up.

I can push the pedal about two to three inches before it gets hard. This is with the engine off. I have not driven the car yet and won't until I am comfortable with the pedal. I keep thinking that I should be able to pump up the pedal (like every other car I've done) so that there is very little movement of the pedal when the engine is off. When I have a helper push the pedal down the brakes are locked, I cannot turn the wheels with a three foot breaker bar.


I have no clue...there must be something stupid here that I am missing. I don't understand why I have to push the pedal down so far before it gets hard....:clonk:
 

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What is the bore size of the MC? The only thing that comes to mind is that if it's smallish, it doesn't have the volume to operate the calipers without a low pedal. Shouldn't be that small being a power MC, though. I've also never heard much good about the Seville rear calipers, either, esp the e-brake. Dont know if that could be your problem or not.
 

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As I recall, that Corvette master cylinder is available in either a 1" or 1 1/8" bore dia. Either should work fine on your setup.

As you know, the e-brake adjustment on those Cadillac calipers can be problematic. The pads should clamp firmly on the rotor with 1/4" or less movement of the arm on the caliper from its stop.

With the wheels off and some lug nuts holding the rear rotors, have a friend pump the pedal. Look for any flex or movement at all in the rotors, calipers, and their mounts. Even a little flex can be felt in the pedal as extra travel.

When I had a '77 Seville, I did the brakes and had the same problem. I checked it out, bled, and adjusted numerous times. What it needed was a little break in time for the pads to fully seat to the rotors. After a few days, it felt and worked great. It had just a little spongy feel at the top of the pedal travel, more than I was comfortable letting my wife drive with.
 

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i`d think the master is maybe on the small side...you have a lot of fluid requirement for all of those calipers...also do you have a residual pressure valve in the system???caliper pistons have a square cut seal on the piston that will retract a bit if there isnt residual pressure there to keep them from retracting...they dont pull in much, but if you have eight pistons total in front, and two pistons rear retracting, you`ll notice it for sure!!!just rereading your post, put the residual pressure valve where you have the threeway flair union block...i bet that`ll cure it...
 

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Discussion Starter #5
What is the bore size of the MC?
1 1/8 bore.


As you know, the e-brake adjustment on those Cadillac calipers can be problematic. The pads should clamp firmly on the rotor with 1/4" or less movement of the arm on the caliper from its stop.

With the wheels off and some lug nuts holding the rear rotors, have a friend pump the pedal. Look for any flex or movement at all in the rotors, calipers, and their mounts. Even a little flex can be felt in the pedal as extra travel.

When I had a '77 Seville, I did the brakes and had the same problem. I checked it out, bled, and adjusted numerous times. What it needed was a little break in time for the pads to fully seat to the rotors. After a few days, it felt and worked great. It had just a little spongy feel at the top of the pedal travel, more than I was comfortable letting my wife drive with.
I don't see much flex anywhere front or back when I have a helper pump the pedal, although I haven't looked at the rears with lug nuts on and the wheels off, just wheels and lugnuts off. I will look at the rears more closely.


i`d think the master is maybe on the small side...you have a lot of fluid requirement for all of those calipers...also do you have a residual pressure valve in the system???caliper pistons have a square cut seal on the piston that will retract a bit if there isnt residual pressure there to keep them from retracting...they dont pull in much, but if you have eight pistons total in front, and two pistons rear retracting, you`ll notice it for sure!!!just rereading your post, put the residual pressure valve where you have the threeway flair union block...i bet that`ll cure it...
1 1/8 is too small? No I don't have a residual pressure valve plumbed in. You are suggesting a residual pressure valve for the rears not the fronts, right?



Thanks for all of the input so far.
 

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I have the vette M/C on a 4 wheel system also. I have the manual version which is a 1" bore (power is 1 1/8"). My pedal also pushes in a fair distance before the pedal really gets hard. with the car started it pushes even further but the brakes work great and under hard braking the pedal is almost perfect for toe heal braking so I like it.
 

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i`d either try a newer master, with residual pressure valve for disc built in, or a low pressure residual pressure valve for the fronts...i think whats happening is the calipers are retracting just slightly...remember that theres alot of surface area there...takes alot of fluid to move those calipers...watch the calipers as a friend actuates the pedal...see if they`re retracting...thats all i can think would crap up the pedal feel...hope this helps...you dont want alot of residual pressure...i believe there are 2 types of valve...get the wrong one, and the brakes will drag...we dont want that...
 

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FWIW:
I have stock '69 front calipers, 79 Seville rear discs and '79 Seville combination valve with '69 power booster and '95 Impalla SS Master cylinder (Dia??) With no power, the pedal travel is 1-3/4" - 2" from top of pedal travel to hard.

TTFN
Mat
 

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Discussion Starter #9 (Edited)
I have the vette M/C on a 4 wheel system also. I have the manual version which is a 1" bore (power is 1 1/8"). My pedal also pushes in a fair distance before the pedal really gets hard. with the car started it pushes even further but the brakes work great and under hard braking the pedal is almost perfect for toe heal braking so I like it.
Thanks for the feedback. I'm in uncharted waters...never set up four wheel disc before, all of my experience is disc/drum.


i`d either try a newer master, with residual pressure valve for disc built in, or a low pressure residual pressure valve for the fronts...i think whats happening is the calipers are retracting just slightly...remember that theres alot of surface area there...takes alot of fluid to move those calipers...watch the calipers as a friend actuates the pedal...see if they`re retracting...thats all i can think would crap up the pedal feel...hope this helps...you dont want alot of residual pressure...i believe there are 2 types of valve...get the wrong one, and the brakes will drag...we dont want that...
I have a two pound residual pressure valve that I could try on the fronts...


FWIW:
I have stock '69 front calipers, 79 Seville rear discs and '79 Seville combination valve with '69 power booster and '95 Impalla SS Master cylinder (Dia??) With no power, the pedal travel is 1-3/4" - 2" from top of pedal travel to hard.

TTFN
Mat
Thanks...I measured the pedal travel with the engine off (no power) and it is just under two inches.
 
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