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Old 04-29-2014, 01:52 PM
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proportioning valve question

My '37 has a non-adjustable valve for front disc / rear drums. I just had front
ceramic pads put in, and new brake shoes in the rear. This car will NOT lock them up in a panic stop. It's like stepping on a sponge 'til it stops. Had them check vac assist, and it's good. They also pulled the brake pedal so they could make sure the actuator at rear of cannister was right. The proportion valve is probably 20 years old. QUESTION : If I put a continuity meter on the output pin
of the valve, should I see continuity to Ground ? Or is that the warning state
because the valve is bad ? It's the only part that hasn't been replaced.

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Old 04-29-2014, 04:31 PM
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Quote:
Originally Posted by Born Again View Post
My '37 has a non-adjustable valve for front disc / rear drums. I just had front
ceramic pads put in, and new brake shoes in the rear. This car will NOT lock them up in a panic stop. It's like stepping on a sponge 'til it stops. Had them check vac assist, and it's good. They also pulled the brake pedal so they could make sure the actuator at rear of cannister was right. The proportion valve is probably 20 years old. QUESTION : If I put a continuity meter on the output pin
of the valve, should I see continuity to Ground ? Or is that the warning state
because the valve is bad ? It's the only part that hasn't been replaced.
The electric terminal is for the differential pressure switch that turns on the BRAKE light on the dash if you get a leak in a brake line. It has nothing to do with normal function of the prop valve. Sponginess is due to air in the lines or a bad M/C.
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Old 04-30-2014, 04:04 PM
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You need to tell us more about what brake system your running. Master cylinder? If you slam your pedal hard what locks up? A proportional valve can be plumbed into your rear brake line.

Last edited by 31chevy; 04-30-2014 at 04:12 PM.
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Old 05-01-2014, 10:08 AM
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You need to tell us more about what brake system your running. Master cylinder? If you slam your pedal hard what locks up? A proportional valve can be plumbed into your rear brake line.
I forgot to mention that they did replace the master cylinder, and they added a
seperate valve near the rear end. It all made a slight difference, but NOTHING will lock up if i try to panic stop. Basically, the whole system is '74 Camaro.
with a 350. Next week, I'm gonna have the use of a lift for as long as I want.
I'm gonna try to sequentially troubleshoot the problem, but I could use a step by step list to go by. Thanx
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Old 05-01-2014, 03:15 PM
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How many miles on the new pads and shoes? Were they properly bedded in? Until new friction seats itself to the rotors or drums brake performance will be less. Also the friction rating of the pad can make a difference. There may be nothing wrong hydraulically at all

Auto guide sucks
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Old 05-01-2014, 03:26 PM
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How many miles on the new pads and shoes? Were they properly bedded in? Until new friction seats itself to the rotors or drums brake performance will be less. Also the friction rating of the pad can make a difference. There may be nothing wrong hydraulically at all

Auto guide sucks
about 500 city miles on the pads so far........... was looking at the setup last night...............there's a few 90 degree turns in the tubing, both front and rear.
And they don't look like they were done with a tool. I wonder how much reduction in psi it might add up to.
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Old 05-02-2014, 10:14 AM
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here's a pic of the tubing from the master cylinder to the prop valve. Each line has almost 360 degrees of bend in 30" of line. I don't know hydraulics, but it must offer resistance to flow ? And the lines look like they were bent by hand.
It wouldn't be a big job to replace them and wind up with about 140 degrees of bend per line. Think it's worth a try ?
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Old 05-02-2014, 11:06 AM
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Some GM cars have brake lines that make a complete 360 under the M/C, to allow flex so the booster can be changed without disconnecting the M/C brake lines. Your minor bends are irrelevant to brake performance, unless you have flattened the line somewhere.

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Old 05-02-2014, 07:43 PM
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Pressure in a hydraulic system will be the same through the whole system as long as the length is reasonable. I used to work on hydraulic systems that worked on as little as two psi over 60 ft. Bends can reduce flow, but have very little effect on pressure. Automotive brake systems do not depend on flow, only pressure.

Were the brakes Okay before you changed the linings? A soft pedal is usually one of two things. Air in the system, or lack of residual valves, or defective residual valves, to hold 2 psi for discs, or 10 psi for drum brakes at the wheel cylinders.

Do the brakes improve if you pump the pedal?
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Old 05-03-2014, 03:11 PM
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Quote:
Originally Posted by Born Again View Post
I forgot to mention that they did replace the master cylinder, and they added a
seperate valve near the rear end. It all made a slight difference, but NOTHING will lock up if i try to panic stop. Basically, the whole system is '74 Camaro.
with a 350. Next week, I'm gonna have the use of a lift for as long as I want.
I'm gonna try to sequentially troubleshoot the problem, but I could use a step by step list to go by. Thanx
So you have an additional valve near the rearend. I think you need to get rid of the 20 year old metering valve, not sure what it's original application was but it was made for for that application. Why is that metering valve being used? You only need the proportional valve plumbed in your rear line close to where you can adjust it front under your seat.
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Old 05-07-2014, 07:29 AM
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I just switched pads from Hawk High Performance Street to CARQUEST Ceramic and I'm experiencing the same thing.. Like the one guy said, maybe they need broken in a little more...

I use an adjustable proportion valve and set it so the rear wheels do not lock up right away..
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Old 05-19-2014, 06:24 PM
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Quote:
Originally Posted by Born Again View Post
here's a pic of the tubing from the master cylinder to the prop valve. Each line has almost 360 degrees of bend in 30" of line. I don't know hydraulics, but it must offer resistance to flow ? And the lines look like they were bent by hand.
It wouldn't be a big job to replace them and wind up with about 140 degrees of bend per line. Think it's worth a try ?
Curious if you got your brake problem sorted out?
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Old 05-20-2014, 07:03 AM
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YES !!! As a matter of fact, just yesterday. Hit it right at Monroe tire co.
Brought it in for an oil leak, and it turned out to be the pan gasket. They called supplier for one, to find it wouldn't be in until this am. The Mechanic was an old timer, and I mentioned the brake problem.He dove right into it.......cleaned and gave the rears a slight adjustment, and secured the front pads. ( tabs were never peaned over ). Then he started bleeding at the Master.....the rear port let out a gush of air...........and that was that. I guess my front calipers were'nt really engaging the rotors. Like most of you said, it's probably a bleed problem.
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Old 05-20-2014, 08:55 PM
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Originally Posted by Bonneville462 View Post
I just switched pads from Hawk High Performance Street to CARQUEST Ceramic and I'm experiencing the same thing.. Like the one guy said, maybe they need broken in a little more...

I use an adjustable proportion valve and set it so the rear wheels do not lock up right away..

*****Follow up*****

The CARQUEST Ceramic brake pads are excellent pads.. They needed broken in a little... I just drove the car and braked lightly to season them... I'm very happy with them...
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Old 05-21-2014, 09:02 AM
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Expensive, but worth it in the long run. What a huge difference in my pedal since he worked the bug out.Locks up like an old car should, when you cram the pedal.
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