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proportioning valve question

3K views 14 replies 7 participants last post by  Born Again 
#1 ·
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.
 
#4 ·
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
 
#5 ·
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
 
#6 ·
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.
 
#7 ·
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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#9 ·
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?
 
#13 ·
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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