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Old 08-20-2006, 02:57:22 PM   #1
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Brake bleeding and proportioning valve help needed

I'm having problems bleeding the brakes on my 76 Camaro and hope someone can help me. I can get brake fluid out my front left bleed screw but not my right rear bleed screw after repeatedly pumping the brake pedal. I haven't tried right front & left rear. I've got leaks around the lines coming out of the proportioning valve even though I've tighten up the lines as much as I dare without potentially damaging them. I'm guessing the problem is with the proportioning valve. I have some questions about the proportioning valve and brake bleeding.

Other info - Brakes lines are all new. The master cylinder, brake booster, calipers and wheel cylinders were all professionally rebuilt. The proportioning or combination valve is original and was thought to be in good condition so it was just cleaned/painted. I'm using Dot 3 brake fluid. I did not bench bleed the master cylinder though I think I going to take it back off and bench bleed it.

What does the metering valve pin on the proportioning valve look like when it is opened or closed and should it move pretty easily? I understand the metering valve pin should be held in when bleeding the brakes and can be done with GM tool J23709 or a similar right angle type bracket. I've never seen the metering valve pin in action and mine appears to be stuck though I don't know if it is stuck open or closed and if it can be unstuck. A picture of mine is below without the rubber cap.

Maybe I pushed the brake pedal too far and over extended the proportioning valve like towhog mentioned in this post though I didn't hear/feel any click or pop in the pedal. If I over extended the proportioning valve, can it be fixed?

80Camaroman has a good post about testing the metering valve but I don't have pressure gauges to do this test. Can most repair shops that do brake work do such a test? I would prefer to use either my original or an original style proportioning valve if possible rather than an aftermarket piece which looks different.

What is really the correct order for bleeding brakes from a totally dry system - nearest to furthest from the master cylinder or the opposite? Maybe it doesn't matter much if you do a good job bleeding. The GM Service Manual notes nearest to furthest. The Chilton manual (and my dad) note that brake bleeding should begin at the right rear wheel, then left rear wheel, then right front, then left front. The Chilton manual also notes "If the master cylinder is equipped with bleeder valves, bleed them first then go to the wheel cylinder nearest the master cylinder (left front) followed by the right front, left rear, and right rear." I never noted any bleeder valves on my master cylinder.


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Old 08-20-2006, 06:37:31 PM   #2
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NEVER use teflon tape on flared fittings.
Thats why they leak. Check the condition of the flared ends on the steel lines while you have them off cleaning the tape off.
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Old 08-20-2006, 07:07:19 PM   #3
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^^^^ Like Mark said - take the teflon tape off!!! The flared fittings are self sealing and do not benefit from any type of sealants. You should pressure flush your entire brake system after you take the tape off and may have to replace the prop valve since you (hopefully not) may have shreds of this tape in it also. BTW...never use this stuff in fuel lines also. I learned my lesson the hard way.

79 Z28 bought new, honeymoon ride same year, still have same wife, same car.
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Old 08-21-2006, 10:32:48 AM   #4
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Thanks for the replies. I removed all the teflon tape. I only used it on about six brake connections. I removed and cleaned all 15 threaded brake connections front and rear just to be sure. I never used anything on the fuel lines.

I don't want to just give up on the prop valve. I've removed it and will see if I can test it and/or disassemble it. I was hoping someone might reply with simple instructions to do this and that and the prop valve should be good to go.

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Old 08-21-2006, 10:46:19 AM   #5
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I found this info about prop valves and am studying it to see if it will help me.
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Old 08-21-2006, 10:58:57 AM   #6
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I just did my prop. valve and my pin sticks out and moves freely. My valve looks just like yours. I have another that is slightly different in that the lines go in at different locations that are plug on our valves. The pin on that one is also out and moves freely. If I remember correctly, my pin only moves outward and springs back inward. At it's most inward point it still sticks out between 1/8 and 1/4 inch. I don't think you can push it in at all, only pull it out. I'm at work right now and can't check it. Anyway I would say that yours is stuck too far inward and probably damaged not allowing fluid to go to the rear brakes. I'm no expert and that is just a guess. I can only say for sure that your's is not in the position that the two I have are.
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