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Old 01-21-2005, 10:48 AM
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OK I'm stumped

I did a 4 wheel brake conversion. Brakes work O.K. but have a wierd problem. When I bleed the rears, the master cyl. gets stuck for a couple of seconds in the depressed position. If I crack the bleeder, the master clicks and goes back to the proper position. I've tried 3 different master cyl. and all do the same thing. The rear calipers are off a T-bird, and call for a 1 1/16 bore master. Thats what I have. The brake system has too much front brake compared to rear, I don't think thats relevant to this problem, but I don't know. Parts are as follows 1986 IROC booster, 1977 corvette master, 75 belair front calipers, 91 t-bird rear calipers. Could someone help me or shoot me, don't really care wich at this point. I've been at this for two days and have no more answers

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Old 01-21-2005, 11:04 AM
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Does the MC plunger stick only when bleeding or does it do it when you apply the brakes? If only the former, sounds like what is happening is the extraordinary fluid loss from the rear chamber in the MC is allowing springs or some other internal widget to collapse and bind. Then the click you hear is the spring releasing the bound coils and returning to 'ready' position. If that's the case, I wouldn't worry about it 'cause that condition can't happen when the brakes are being applied during driving.

And you want more brakes in front than in back, trust me!
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Old 01-21-2005, 11:29 AM
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brakes

Do you have the proportioning valve installed? You may need an adjustable one. Also make sure that all caliper bleed screws are at the top,otherwise they will not bleed properly. also may need residual check valves.
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Old 01-21-2005, 12:14 PM
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Some disc/drum master cylinders have a built in residual pressure valve for the drum brakes. This keeps some pressure on the rear drums so the cylinders stay ready to stop.

If you are running all disc brakes and you have a residual valve from the old drum brakes in the master cylinder you may have a problem. That is why companies list the set up when selling the master cylinders.
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Old 01-21-2005, 12:29 PM
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I assumed '77 'Vettes had 4-wheel disk brakes. If not, there probably is a 10psig residual valve in the rear outlet. However I can't envision how the residual valve would cause the problem he describes. It would cause brake drag for sure on disk brakes.
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Old 01-21-2005, 01:07 PM
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the vette does have 4 disks. The bleeders are correct. The rear calipers have a built in park brake. The problem with leaving it as is, is if the rear brakes wear out and the driver is not using his park brake regularily, the pedal will get increased travel and eventually duplicate the problem under a driving condition.

the calipers aren't hanging up, only the master is not retracting. There seems to be a suction created in the line because the caliper does not retract far enough to release the master. I don't have a proportioning valve in the rear, but i don't see how that would make a difference to my problem. The brakes actuate great when the master finally pulls back all the way.

thinking out loud here. If the park brake mechanism is not allowing the caliper to retract far enough would it cause the problem? I'm not too familiar with how that system works. I know it is a screw actuator. Does this limit the amount that the caliper can retract when the park brake is disengaged?

Last edited by Kurt; 01-21-2005 at 01:06 PM.
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Old 01-21-2005, 01:10 PM
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Tried to delete my post but it won't let me ???
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Old 01-21-2005, 01:24 PM
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Is there bindng in the pedal assembly?

The power brake booster moves correctly?

Are you bleeding with the engine running/booster working?
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Old 01-21-2005, 01:44 PM
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pedal assembly moves freely. The pedal does drop some when the engine is running, probably a little more than it should, but it doesn't seem too bad. Bleeding with the engine running seems to accentuate{wow thats a big word} the problem. Does anybody know the inner workings of the park brake assembly? Can the piston move away from the screw portion ? I am going to try disadjusting the park brake a bit to allow the caliper to retract farther. Does this make sense?
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Old 01-21-2005, 02:14 PM
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Any way you can disconnect the front, push pedal, then rear and see if the pedal returns on either to pinpoint which circuit may be the culprit?
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Old 01-21-2005, 02:25 PM
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Also make sure that all caliper bleed screws are at the top,otherwise they will not bleed properly.
I hope you don't mind me jumping on your thread, but Jerry, can you explain this issue? I've installed '79 El Dorado calipers on my Nova, not realizing this would be an issue.

I've searched the KB and Internet and can't find any reference to it. I haven't gotten to the bleeding point; can the system be bled, (my brackets are big time welded to a 4-link rear, not easily changed) - is there a work around or am I doomed?

Thanks, Larry
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Old 01-21-2005, 02:39 PM
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My bleeders are on the wrong side of the calipers on my Willys so I unbolt then, slip them onto the disks so the pistons don't come out and with the bleeders looking up, bleed them, then bolt them back in place. No big deal.
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Old 01-21-2005, 02:47 PM
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I obviously didn't take enough time to figure this out Willys, thanks!

Shoot, that's way easier than tipping the car over, I like it!


Larry
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Old 01-21-2005, 03:10 PM
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bleed screw position

As you know air rises to the top,and the bleeders must be where the air can escape. Is your M/C below the calipers, if so 2lb residual valves must be used front and rear to keep fluid from draining back. Hope this helps. Brakes can be a headache at times. Good luck
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Old 01-21-2005, 05:06 PM
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Shoot, that's way easier than tipping the car over, I like it!



Great response
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