no pressure to rear brake lines on 67 - Team Camaro Tech
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post #1 of 23 (permalink) Old Feb 2nd, 09, 05:46 AM Thread Starter
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no pressure to rear brake lines on 67

Guys - 67 with stock drums all the way around - I have the two piece front to rear line with the proprotion valve on the frame rail under drivers seat.

Confused. Had a soft pedal to the floor and a leak in my right rear wheeel cylinder. Replaced cyclinder - went to bleed and had no pressure in the line. Helper pumped the brake pedal and I checked if I had pressure in the other side rear and had none there as well. This other side is a relatively new wheel cylinder and I know has been functioning. What could have reacted to my loss of pressure when the wheel cyl leaked and essentially shut down my rear lines? Could that proportion valve under the drivers seat have done this? Master cylinder react in some way...or did my master cylinder suddenly die?

Any thoughts on how to proceed here greatly appreciated....thanks to all my firends here....JD
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post #2 of 23 (permalink) Old Feb 2nd, 09, 06:31 AM
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Re: no pressure to rear brake lines on 67

It could be a few things I would first check ifyou have presure at the master to the rear lines. Have a freind put preasure on the pedal then crack loose the rear lineat the master. Note : cover everthing up to protect paint well! If you have psi there move further down the line near the valve. Could you have run out or very low on fluid with your leak? It could be the over the axle flexable ruber line aswell, Change it anyway if its original.
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post #3 of 23 (permalink) Old Feb 2nd, 09, 09:21 AM Thread Starter
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Re: no pressure to rear brake lines on 67

Good thoughts...but I forgot one cructial piece of information leading to my confusion. Although I have no pressure in the rear..I have hard pedal! The softness of the pedal that was present when the rear wheel cyl leaked has firmed up....with a strong pedal. I wouldn't think it would be an issue of loosing too much fluid when the original leak started, if I now have hard pedal??? It's as if I have become blocked somewhere from the proportioning vlalve up to the master cylinder.
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post #4 of 23 (permalink) Old Feb 2nd, 09, 10:53 AM
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Re: no pressure to rear brake lines on 67

First off, I'm wondering what a proportioning valve is doing on a drum brake car?....This valve is only for disc/drum cars.....There should only be a distribution block, located under the master cylinder, on a drum brake car!.....Assuming that all brake lines and hoses are not bent or kinked, I'd probably be looking at a defective master cylinder and that's assuming that the brake pedal pushrod is properly adjusted!
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post #5 of 23 (permalink) Old Feb 2nd, 09, 11:01 AM
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Re: no pressure to rear brake lines on 67

Ron, '67 A/C drum brake cars could have the prop valve. Mine does, although A/C is long gone.

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post #6 of 23 (permalink) Old Feb 2nd, 09, 11:04 AM
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Re: no pressure to rear brake lines on 67

Quote:
Originally Posted by rojo View Post
Ron, '67 A/C drum brake cars could have the prop valve. Mine does, although A/C is long gone.

OK Robert, I wasn't aware he had A/C!....Will you forgive me??
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post #7 of 23 (permalink) Old Feb 2nd, 09, 11:06 AM
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Re: no pressure to rear brake lines on 67

Sure

Of course I don't know if he has A/C either.

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post #8 of 23 (permalink) Old Feb 2nd, 09, 11:09 AM
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Re: no pressure to rear brake lines on 67

Thanks!!
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post #9 of 23 (permalink) Old Feb 2nd, 09, 11:13 AM
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Re: no pressure to rear brake lines on 67

I have had many problems trying to bleed rear brakes if fronts had pressure. I think I would first try to gravity bleed it. The other possibility is the proportioning valve might be stuck, if indeed that is a prop valve located only in the rear line. I always thought a proportioning vale worked with the pressure from both lines and when it got too far out of balance it shut off one side.

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post #10 of 23 (permalink) Old Feb 2nd, 09, 11:14 AM Thread Starter
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Re: no pressure to rear brake lines on 67

Guys..Yes I have a 67 AC car...and the valve is part of this setup as it is on 68 and later higher performance setups....if I recall GM engineers evaluated the valve on 67 cars that had AC due to the slightly heavier weight....

I am just wondering if this valve could have failed/clogged....
I guess I'll break the lines loose from the valve tonight and see if I get flow...
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post #11 of 23 (permalink) Old Feb 2nd, 09, 11:16 AM Thread Starter
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Re: no pressure to rear brake lines on 67

Jeff...I guess that is the heart of the matter...I don't know how this valve really works internally either, or if ican actually **** down one side. If so, maybe I should bleed the fronts some and the valve will open up...?? grasping at straws here....
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post #12 of 23 (permalink) Old Feb 2nd, 09, 11:18 AM Thread Starter
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Re: no pressure to rear brake lines on 67

Jeff....Gravity bleed? Sorry, not quite sure what a gravity bleed is...??
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post #13 of 23 (permalink) Old Feb 2nd, 09, 11:24 AM
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Re: no pressure to rear brake lines on 67

Gravity bleed is when you crack open a bleeder valve and let gravity take over in the bleeding process but you need to make sure to check the master so that it doesn't run dry of brake fluid!
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post #14 of 23 (permalink) Old Feb 2nd, 09, 01:01 PM
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Re: no pressure to rear brake lines on 67

Your valve has a low pressure warning switch. Most likely when your rear cylinder "leaked" it shut off the rear circuit. You'll need to re-center the valve. You can take it apart to do this or open a front and a rear at the same time and bleed, the valve should re-center(equalize pressure). Did the light on the dash come on?
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post #15 of 23 (permalink) Old Feb 2nd, 09, 04:03 PM Thread Starter
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Re: no pressure to rear brake lines on 67

OK..interesting. I know there is a switch at the junction box that is right under the master cylinder..is this what you are talking about? The valve I was referring to is under the drivers seat located on the subframe rail. Does the junction box have the ability to modify pressure....?......I thought it was just a passive junction box.
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