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Old 08-21-2010, 10:58 AM
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bad master cylinder

I'm not sure what's wrong. I installed a new four wheel disc brake system on my Nova. I bench bled the master cylinder and then reinstalled it in the vehicle. This is my fiirst time installing a whole new system and I'm a little confused. Is there a trick to hooking up the lines when you remove the bleeder kit and put the m/c back in the car? Doesn't removing the bleeder kit just let air back in and ruin the work you did?

Also, now that the m/c is back in the car I am having no luck bleeding the brakes. When I pump the pedal, no pressure builds up and the fluid level in the reservoir does not go down. I hooked up the rr bleeder to a hose and put it in a cup with some fluid in it. Had a helper pump the pedal and then I cracked the bleeder and not even any air bubbles come out. I sucked on the tube air comes out so the line is not blocked. Is the m/c bad, or does it sound like the bench bleeding wasnt performed right or what? Also, if I were going to try to gravity bleed it, how long should I have to wait to start seeing fluid come out the bleeder?

I know I asked several questions, but hopefully someone can help point me in the right direction.

Thanks,
Chris

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Old 08-21-2010, 07:36 PM
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[QUOTE=ckliever]I'm not sure what's wrong. is there a trick to hooking up the lines when you remove the bleeder kit and put the m/c back in the car? Doesn't removing the bleeder kit just let air back in and ruin the work you did?


Very perceptive and the answer is ...not if fluid is running out of it while you are hooking it up. If you did not have fluid dripping out then chances are there was a bunch of air left in it.
What i sometimes do if i have a stubborn master is with it on the car I will "tap" the brake pedal gently without moving it too far . Basically only moving the brake pedal a little so as to just tap the master cylinder plunger. are you with me so far.Do this very easy like . If you want to see why, have your buddy tap the pedal and watch the fluid in the master.Each time he taps it you will see an air bubble come up. DONT PUSH DOWN ON THE PEDAL OTHER THAN TAPPING ON IT AT THE TOP OF ITS TRAVEL. BECAUSE when you let off of the pedal if you do...you will have a brake fluid fountain and will get it all over. After you do this little tap thing put the lid on and GENTLY pump the pedal 2-3 times to see if enough air has escaped to aid in the normal bleed procedure. I know this doesnt make much sense and doesnt sound quite normal but it is easy and it works on tough bleed problems like clutch masters especially.More times than not I have bled clutches this way and it works better than pumping and bleeding . Pumping too fast can actually pull air in past the secondary seal in the master in some cases.it also works on air locks in stubborn brake masters.
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Old 08-21-2010, 07:40 PM
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Also once you get a pretty good pedal ,I do prefer to gravity bleed the system as pumping also causes air to be suspended in the fluid if you get too foot happy ( pumping to fast /hard). Gravity bleeding dismisses the issue.
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Old 08-22-2010, 12:29 AM
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Thanks for the response. Ok, so I re-bench bled the m/c and I'm confident that it was air-free. I placed it back in the car and connected the lines to the proportioning valve. I wouldn't say fluid was "running out" of the m/c but maybe it was "weeping" - just a tiny trickle soaking into my rag while I tightened the lines.

So now that it's back in the car I tried to bleed the lines again, and I still am having no luck. I went out and bought a vacuum pump to try to speed things along and identify any problems. I started in the right rear but couldn't get anything. I discovered along the way that three out of four bleeder valves couldn't hold vacuum when completely closed I put teflon tape on them and that seemed to work. I moved up front just to see if I would have any better luck there, and I could get some fluid flowing but no matter how long I pump, there is still tons of air coming through. I filled the reservoir about three times while working the front left. How long should it take to get the air out? My system is all brand new stuff from classic performance. The m/c is split for front and rear. I cant imagine that it would take this much pumping to get the air out of the front.

One more thing, after bleeding the front left a while, I closed off the bleeder and while there was still vacuum in the pump, I could see a slow stream of bubbles coming from the bleeder. Is this a bad bleeder? I tested the pump on one of the other bleeders by leaving some fluid in the pump hose and then raising the vacuum and there weren't the stream of bubbles, only on the front left.

I'm pretty frustrated at this point...
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Old 08-22-2010, 07:44 AM
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It does sound like the bleeder you described is not holding for whatever reason.
Also remember what I said about pumping too aggressivley, air being pulled in throught the seals at the master, the vacuum pump may be doing that and pulling air in past the hose where it is hooked to the bleeder plus it can pull air past the threads when they are open. Did you check all your line connections to make sure they are good and tight. A flare fitting needs to be tightened to seat it well to the fitting it is placed in. Also does this system have a proportioning valve? or do you have a regulator to the rear? Maybe there is a problem with that. Sounds like you got the master bled well enough to continue. I was concerned about the fluid getting on the paint anyhow ( I am sure you were too) so move to the rest of the system.
Try to bleed it at the proportioning valve next to see if: 1 the master is making pressure for both systems and 2 if you get fluid to the prop valve then check on the output side for fluid flow to see if the valve shuttled and blocked off one system or if it is flowing through both sides of the valve.After all... the prop valve shuttles to one side when the pressure is lost on front or rear systems to block the flow so you still have one set of brakes that works.they will stick when they have been shuttled even if new.Pumping too aggressively on a bleed procedure can shuttle it when you start to get pressure building on one system thus blocking the other and creating insanity.Keep us posted
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Old 08-22-2010, 07:48 AM
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My brother had his son replace the MC, both front calipers and new shoes on the rear of his Dodge motor home, they couldn't get it to bleed either. When I arrive to help I saw the front caliper bleeders weren't on top, they had swapped the calipers left to right. The bleeder needs to be at the top. We bench bled twice, and bled lines four or five times before I realized they were on wrong. He had no pedal during all this bleeding. Just a thought.
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Old 08-22-2010, 08:03 AM
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Place the top cover and rubber on, and you can remove the bleeder kit and no fluid will run out. The reason is the system is sealed with the cover in place.

Gravity bleed is a good option and one I use myself, especially on a new system. Those vac pumps are tricky, have used them on floor mounted MCs but in your case to make life easier stick with the gravity bleed, it will work just give it some time, it starts out slow, do not have any fluid in the container you have at the wheel cylinder and also give the bleeder a couple of turns out for a good air/fluid flow..out. To see it working watch the MC you will see the fluid level start to go down.

Good point about the location of the bleeder and caliper orientation, he did say he was a first timer.
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Old 08-22-2010, 11:53 AM
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Thanks for all the tips. My calipers on on the correct sides with the bleeders up. I started systematically checking vacuum on all the lines. I get fluid through the proportioning valve just fine and I could get fluid back to the rear T junction no problem. From that point I have a leak to the right rear. Looks like my 3/16 flare wasn't up to par. I'm going to get some new line and re-flare it and go from there. I hope that I'm on the right track.
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Old 08-22-2010, 01:36 PM
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Good deal. Glad to see you're on top of that. You can be driving tonight. Best of luck. Latech
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Old 08-22-2010, 05:49 PM
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You know that brake fittings require the double flare?
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Old 08-23-2010, 05:29 PM
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Yah mine was a double flare but I guess just not nice enough. I took more care filing the line square before I flared it this time and they worked. I vacuum tested them off the vehicle and they are good. I reinstalled them yesterday but didn't have time to bleed the system. I'm going to give it hopefully the final shot tonight. Thanks for all the help. I'll let you know how it goes.
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