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Discussion Starter #1
1970 Nova. Replaced the ENTIRE brake system with a Right Stuff Detailing disc brake conversion set, including all new stainless hard lines. So all new rotors, calipers, pads, hard lines and high pressure lines, new proportioning valve, new master cylinder and a new power booster. Everything was replaced.

After fixing a few leaks I finally got the system to bleed. No air after going round and round and the pedal feels pretty good.

Thinking I was done, I put the wheels back on, and fired up the car. As soon as the engine starts and I get vacuum to the booster, the pedal goes to the floor. No apparent lose of fluid, and no leaks that I can see.

What gives?

Thanks, Bart
 

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1970 Nova. Replaced the ENTIRE brake system with a Right Stuff Detailing disc brake conversion set, including all new stainless hard lines. So all new rotors, calipers, pads, hard lines and high pressure lines, new proportioning valve, new master cylinder and a new power booster. Everything was replaced.

After fixing a few leaks I finally got the system to bleed. No air after going round and round and the pedal feels pretty good.

Thinking I was done, I put the wheels back on, and fired up the car. As soon as the engine starts and I get vacuum to the booster, the pedal goes to the floor. No apparent lose of fluid, and no leaks that I can see.

What gives?

Thanks, Bart
So just sitting there and starting the motor you can watch the brake pedal go down to the floor ? and then once the motor is shut off the brake pedal comes back up ?.

When this happens do all 4 corners of the brakes lockup preventing the car from moving or if it's up in the air, are all 4 tires not rotating ?

Did you make sure the "kit" had all of the right part numbers in the kit ?. I've purchased things and while 90% of the parts were correct,the 10% that were not right for the kit made things screw up.

Jim
 

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72, 2 Dr, 383, 700r4
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So just sitting there and starting the motor you can watch the brake pedal go down to the floor ? and then once the motor is shut off the brake pedal comes back up ?.

When this happens do all 4 corners of the brakes lockup preventing the car from moving or if it's up in the air, are all 4 tires not rotating ?

Did you make sure the "kit" had all of the right part numbers in the kit ?. I've purchased things and while 90% of the parts were correct,the 10% that were not right for the kit made things screw up.

Jim
I'm not saying this is you're problem but with those kits you have to go backwards and research that each and every item in the kit is compatible. Not only with itself, but you're car. I too dealt with that 10%.
 

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Discussion Starter #4
So just sitting there and starting the motor you can watch the brake pedal go down to the floor ? and then once the motor is shut off the brake pedal comes back up ?.
No, the pedal does not move on it's own, lol. What I mean is, the car is off, I bleed the brakes, get a nice firm pedal. Then as soon as I start the car, and vacuum is applied to the booster, I can press the pedal all the way to the floor like I have no brakes. I have not taken the car out of the garage as I do not know if I have braking power or not, and my driveway is on an incline so I am hesitant to try backing out not knowing if the brakes are up to snuff.

I will add that I have found numerous references to this exact problem all over the Internet but with no real definitive answer. I am going to call Right Stuff tomorrow and see what they say.

I bench bled the MC twice, so I really don't know what it could be. I tried bleeding again but I don't get anything but clear fluid now...

I am a bit stumped...any annoyed because this should be pretty simple.

Thanks.
 

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No, the pedal does not move on it's own, lol. What I mean is, the car is off, I bleed the brakes, get a nice firm pedal. Then as soon as I start the car, and vacuum is applied to the booster, I can press the pedal all the way to the floor like I have no brakes. I have not taken the car out of the garage as I do not know if I have braking power or not, and my driveway is on an incline so I am hesitant to try backing out not knowing if the brakes are up to snuff.

I will add that I have found numerous references to this exact problem all over the Internet but with no real definitive answer. I am going to call Right Stuff tomorrow and see what they say.

I bench bled the MC twice, so I really don't know what it could be. I tried bleeding again but I don't get anything but clear fluid now...

I am a bit stumped...any annoyed because this should be pretty simple.

Thanks.
I think the issues you are having is with the additional force generated by the power assist it is "finding" the remaining air in the system. I used a vacuum bleeder and had to bleed the living daylights out of it before i got a good pedal when I did the same project. Also, need to ask, did you bench bleed the master?
 

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Discussion Starter #6
did you bench bleed the master?
Yes, twice...

Could it be something with with the pedal adjustment rod or maybe the check valve in my brake booster vacuum line pulling to much vacuum?

Car off, nice firm pedal.

Car on, pedal can be depressed to the floor like I have no brakes at all.

Car off again, pump pedal a little and goes firm again.

So it is definitely the vacuum causing the symptom, I just don't know why.

Thanks.
 

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Is this 4 wheel discs , or front discs rear drums? remember discs need to be pumped up to get the pistons out to where the pads will contact the rotors. also if it is rear drum, make sure the shoes are adjusted. and if rear discs, don't they have to be adjusted?
 

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Discussion Starter #9
Is this 4 wheel discs , or front discs rear drums? remember discs need to be pumped up to get the pistons out to where the pads will contact the rotors. also if it is rear drum, make sure the shoes are adjusted. and if rear discs, don't they have to be adjusted?
It's a 4 wheel disc brake system. The pads are making contact with the rotors all around. The calipers are not on the wrong wheels. All bleeders point up. Thanks.
 

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Mike - 74 Nova Baltimore, MD
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Car off, nice firm pedal.
Car on, pedal can be depressed to the floor like I have no brakes at all.
Car off again, pump pedal a little and goes firm again.
So it is definitely the vacuum causing the symptom, I just don't know why.
When you stated that "all bleeders point up"... did you mean that all bleeder valves on the brake calipers are positioned at the TOP of the calipers when mounted on the caliper brackets?

You will need to raise the tires off the ground and have someone to assist you with the trouble shooting procedures shown below.

With the engine off, push on the brake pedal and hold (should be firm again - as you had stated). While holding the brake pedal, have someone try using some force to spin the tires. Do any of the tires spin?... or all they all being held when depressing the brake pedal?

Repeat the above procedures, but this time with the engine running and using the power assist.
Any changes?

And one other thing to check while the engine is running and depressing the brake pedal. Look at ALL of the rubber brake hoses while someone else depresses the brake pedal with the engine running. See if any of the rubber brake hoses appears to be ballooning as the brakes are applied.

A similar situation happened to a friend of mine. It turned out to be that one of his front caliper brake hoses was defective and would expand like a balloon when he hit the brakes... causing the brake pedal to go to the floor when using the vacuum assist booster.
 

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Discussion Starter #11
When you stated that "all bleeders point up"... did you mean that all bleeder valves on the brake calipers are positioned at the TOP of the calipers when mounted on the caliper brackets?
Yes, correct.

You will need to raise the tires off the ground and have someone to assist you with the trouble shooting procedures shown below.

With the engine off, push on the brake pedal and hold (should be firm again - as you had stated). While holding the brake pedal, have someone try using some force to spin the tires. Do any of the tires spin?... or all they all being held when depressing the brake pedal?

Repeat the above procedures, but this time with the engine running and using the power assist.
Any changes?

And one other thing to check while the engine is running and depressing the brake pedal. Look at ALL of the rubber brake hoses while someone else depresses the brake pedal with the engine running. See if any of the rubber brake hoses appears to be ballooning as the brakes are applied.

A similar situation happened to a friend of mine. It turned out to be that one of his front caliper brake hoses was defective and would expand like a balloon when he hit the brakes... causing the brake pedal to go to the floor when using the vacuum assist booster.
Thanks, I will give this a shot. I suppose if the brakes grab both with the engine off and on, then the issue could be the pedal adjustment? I know for sure the brakes work when the car is off, as I did this exact test yesterday while the car was still up on jack stands. But I did not do it with the engine running.

Thanks.
 

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I am pretty sure the vacuum diaphragm holds some residual vacuum when the car is off in case it dies when you are driving to allow some vacuum assist in an emergency. So if you pump it a few times it eliminates it and gives you that firm pedal feel. As soon as you start the car it will pull vacuum and give you the vacuum assist that sends your pedal to the floor. There is still air in the system somewhere, or a mechanical issue causing the pedal problems.

I had a similar issue due to a faulty proportioning valve that closed off the front system and only operated the rear drums. Not your problem but highlights that it can be a bunch of different things causing it.
 

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I'm going to bet air is still in the system. It's not easy to get all the air out when you replace that many parts of a brake system. In the past I used a handheld MityVac to suck the air out, it was hell! I switched to the Phoenix bleeder, it pushes the fluid & air to the master cylinder to exit there. Start at the right rear, left rear next, right front then left front. Better & quicker results. You will need a helper to keep a watch on the master cylinder to watch for air & to be sure it doesn't spill over.

Mike
 

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Discussion Starter #14
I am pretty sure the vacuum diaphragm holds some residual vacuum when the car is off in case it dies when you are driving to allow some vacuum assist in an emergency. So if you pump it a few times it eliminates it and gives you that firm pedal feel. As soon as you start the car it will pull vacuum and give you the vacuum assist that sends your pedal to the floor. There is still air in the system somewhere, or a mechanical issue causing the pedal problems.

I had a similar issue due to a faulty proportioning valve that closed off the front system and only operated the rear drums. Not your problem but highlights that it can be a bunch of different things causing it.
So do you think there could still be air in the lines even though I am not getting any air bubbles when I bleed the calipers?

Thanks.
 

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So do you think there could still be air in the lines even though I am not getting any air bubbles when I bleed the calipers?

Thanks.
I am thinking so. when I replaced all the lines it took forever to get the air all out. couldnt get it out by manually bleeding alone, needed a vacuum bleeder to do so. Also had to put some sealer on the bleeder threads when using a vacuum style bleeder because it would pull air through the threads while bleeding. You might be able to rent one from somewhere, or good old harbor freight can always help. Good luck!
 

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Also as you are bleeding them, tap on the calipers a little with a wrench, to help release any traped air. I always use a pressure bleeder.
 

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Discussion Starter #17
Also as you are bleeding them, tap on the calipers a little with a wrench, to help release any traped air. I always use a pressure bleeder.
I do have a Mighty Vac...maybe there is air in there still. Will hopefully have time later today to get under there again and work on it.

Thanks.
 

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When you are using the "pump the brakes and hold" method of bleeding your brakes, there are a couple of things to consider.

Never let your master cylinder run out of brake fluid during the bleeding process. If you do, you'll have to start all over since air has gotten into the braking system.

You want to slowly pump your brakes to build pressure while bleeding. I was taught that if you are quickly pumping your brakes during the bleeding process, you may introduce some air bubbles into the brake fluid within your master cylinder.

As you are holding pressure on the brake pedal and then loosen the bleeder valve to release the air and/or brake fluid from the calipers, keep the brake pedal on the floor until you have re-tightened the bleeder valve on your caliper. If you let the brake pedal raise before you have tightened the bleeder valve (or you just leave the bleeder valve open), you could be sucking air back into the caliper thru the bleeder fitting threads... as previously mentioned.
 

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I did same full replacement with Right Stuff kit on my 69. 1. You could be pulling air into the system thru a loose connection or faulty brakeline. I replaced all my lines I had that problem. 2. With those calipers make sure the bleeder valve is at the top and perpendicular to the floor - it can’t be fully bolted in place to achieve that position. 3. Use vice grips to pinch off the rear line by the differential after bleeding and then test. If softness comes back in you know it’s in the front, else in the rear. Replace your rear rubber brakeline if it’s not new.
 

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On bleeding, I've had more luck with gravity bleeding than any kind of pumping the brakes or mityvac. Bench bleed a new MC and then gravity bleed starting at the wheel farthest away from the MC and work your way up.
 
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