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Old 08-26-2007, 05:20 AM   #1 (permalink)
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Unhappy Proportioning valve: symptoms of being bad

What are the possible symptoms of a bad proportioning valve?

I have replaced every part of my braking system except the proportioning valve and the brake pedal assembly itself. Everything else is new.
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Old 05-02-2008, 02:14 AM   #2 (permalink)
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Question Re: Proportioning valve: symptoms of being bad?

BUMP - HAS NO ONE HAD THEIR PROPORTIONING VALVE GO BAD? What were the symptoms?
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Old 05-02-2008, 10:47 AM   #3 (permalink)
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Default Re: Proportioning valve: symptoms of being bad

Tough for a prop valve to go bad. There isn't much to it. If it stopped working you'd either have consistent rear wheel lockup or no rear brakes at all.

What are your symptoms? Why have you been replacing brake system parts?

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Old 05-02-2008, 11:00 AM   #4 (permalink)
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Default Re: Proportioning valve: symptoms of being bad

I had a proportioning valve go bad in my chevy blazer and the only the front brakes would work. The brakes also had a tendency to lock up pretty easily without help from the rear. This is a different animal though.
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Old 05-02-2008, 12:14 PM   #5 (permalink)
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Exclamation Re: Proportioning valve: symptoms of being bad

Quote:
Originally Posted by Struggly View Post
Tough for a prop valve to go bad. There isn't much to it. If it stopped working you'd either have consistent rear wheel lockup or no rear brakes at all.

What are your symptoms? Why have you been replacing brake system parts?

Clint
Before reading the rest keep this in mind: I didn't know about brakes a long time ago and the car probably went almost 100k without a brake fluid line flush and also the brakes were used on at least 2-3 occasions while submerged in flood waters.

Symptoms:
  1. Extreme (half as much as normal) insufficient braking power.
  2. Pads scrap rotors despite free turning wheels when jacked up.
  3. Car pulls hard left (but this changes at times to soft left or even right)

ALL brake system components replaced except the prop valve and brake pedal itself. Slider bolts freshly greased to proper grease amount per caliper. MC rebuilt. Replaced booster. All 4 calipers BRAND NEW. Lines bled in correct order with car on several times. New SS lines. No leaks. NO ABS.

I used to have consistent slanted wear on my rears with every pad used. As of late though I think I've identified it as a factory defect. If you use a small ruler and measure the length of the slider bolt boots the length of the top most boot is 1 hash mark on the ruler longer than the length of the boot on the bottom. If the sliders are uneven (which it appears to be due to the thickness of the rubber boot at top slider bolt) this to me would cause the rears to over time slant with the thinnest part of the pad being at the bottom of the caliper and thickest part of the pad at top. The 1 piston design in my NA is also to blame as I believe this problem would be solved with 2 pistons for the rear.
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Old 05-02-2008, 12:31 PM   #6 (permalink)
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Default Re: Proportioning valve: symptoms of being bad

Quote:
Originally Posted by ProwlerGT View Post
Before reading the rest keep this in mind: I didn't know about brakes a long time ago and the car probably went almost 100k without a brake fluid line flush and also the brakes were used on at least 2-3 occasions while submerged in flood waters.

Symptoms:
  1. Extreme (half as much as normal) insufficient braking power.
  2. Pads scrap rotors despite free turning wheels when jacked up.
  3. Car pulls hard left (but this changes at times to soft left or even right)

ALL brake system components replaced except the prop valve and brake pedal itself. Slider bolts freshly greased to proper grease amount per caliper. MC rebuilt. Replaced booster. All 4 calipers BRAND NEW. Lines bled in correct order with car on several times. New SS lines. No leaks. NO ABS.

I used to have consistent slanted wear on my rears with every pad used. As of late though I think I've identified it as a factory defect. If you use a small ruler and measure the length of the slider bolt boots the length of the top most boot is 1 hash mark on the ruler longer than the length of the boot on the bottom. If the sliders are uneven (which it appears to be due to the thickness of the rubber boot at top slider bolt) this to me would cause the rears to over time slant with the thinnest part of the pad being at the bottom of the caliper and thickest part of the pad at top. The 1 piston design in my NA is also to blame as I believe this problem would be solved with 2 pistons for the rear.
Fuckin' a, that's a comprehensive diagnosis...

At rest, pads should contact the rotors with enough pressure to prevent the wheels from spinning multiple times if you spin them by hand. I trust that the scraping is out of the ordinary?

Who rebuilt the MC? DIY or bought rebuilt? How does the pedal feel? Loss of braking power would lead me to fault the MC if you hadn't given me the background.

You could replace the prop valve if you wanted--it's not an expensive part. But your symptoms don't sound like a fucked prop valve to me.

Clint
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Old 05-02-2008, 01:09 PM   #7 (permalink)
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Default Re: Proportioning valve: symptoms of being bad

Quote:
Originally Posted by JohnWattVR4 View Post
I had a proportioning valve go bad in my chevy blazer and the only the front brakes would work. The brakes also had a tendency to lock up pretty easily without help from the rear. This is a different animal though.
Regardless of vehicle all combination valves work the same. Now a proportioning valve alone and a metering valve alone don't include necessarily the same functions of the combo valve which includes all their functions though the terminology is used interchangeably/loosely due to the lack of info out there on it.
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Old 05-02-2008, 01:23 PM   #8 (permalink)
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Default Re: Proportioning valve: symptoms of being bad

Quote:
Originally Posted by Struggly View Post
Fuckin' a, that's a comprehensive diagnosis...
Thats the only way I roll unfortunately and lately its much more of a curse than a gift. I feel if I leave something out it will only get asked about later so I try to cover it all up front.

Quote:
Originally Posted by Struggly View Post
At rest, pads should contact the rotors with enough pressure to prevent the wheels from spinning multiple times if you spin them by hand. I trust that the scraping is out of the ordinary?
Yes. I believe its causing the car to drag-steer to the left and it even seems like its interfering with acceleration.

Quote:
Originally Posted by Struggly View Post
Who rebuilt the MC? DIY or bought rebuilt? How does the pedal feel? Loss of braking power would lead me to fault the MC if you hadn't given me the background.
If you take a look at my revival thread (link in sig) I show detailed pics of how I rebuilt the MC with a kit from Mitsu. Its all done to spec. Entire MC is new except for of course the body which just is a body in good shape.

I feel myself struggling to get the car to stop and this is only after a 20 - 35mph ride literally around the block. There was actually an amazing wonderful (ha ha - yeah right) coincidence when I took it out for a drive for the 2nd time in years... an Armadillo was DEAD CENTER of the street and I was looking away for one second at someone I thought was driving suspiciously behind us..... my sister yelled STOPPP yer gonna hit that thing and so I experienced a panic brake and it was not at all near what it should be. If it weren't for the slow speed there is no doubt the brakes would've failed me into hitting that stupid animal.

Quote:
Originally Posted by Struggly View Post
You could replace the prop valve if you wanted--it's not an expensive part. But your symptoms don't sound like a fucked prop valve to me.

Clint
There is nothing else to replace. The only thing stopping me from doing it is the refusal to believe its bad, but when you've replaced EVERYTHING else I have no earthly idea what it could be.

With brand new calipers are you supposed to pop the pistons out and lube the piston/bore walls with brake fluid? I didn't do this when I got them, but it seems like they'd self lube after the first few brake uses.

Last edited by ProwlerGT; 05-02-2008 at 01:29 PM.
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Old 05-02-2008, 05:14 PM   #9 (permalink)
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Default Re: Proportioning valve: symptoms of being bad

Prowler , did you bench bleed the MC before you installed it ? A quick check on the proportioning valve is to do a few stops from 35mph and carefully check the rotors for heat soak . If the fronts are equally hot and the rears are barely warm then thats your answer , Prop valve NFG . Conversely if one rotor is considerably hotter on either the front or the rear, than the other it would appear that you have a seized piston in the that caliper . Good Luck Steve.
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Old 05-02-2008, 05:26 PM   #10 (permalink)
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Talking Re: Proportioning valve: symptoms of being bad

Quote:
Originally Posted by Dago Red Vr-4 View Post
Prowler , did you bench bleed the MC before you installed it ? A quick check on the proportioning valve is to do a few stops from 35mph and carefully check the rotors for heat soak . If the fronts are equally hot and the rears are barely warm then thats your answer , Prop valve NFG . Conversely if one rotor is considerably hotter on either the front or the rear, than the other it would appear that you have a seized piston in the that caliper . Good Luck Steve.
If bench bleed means bleeding the MC with the 2 lines off of it then yes I did though I really don't see what that bought me as the entire system was empty anyway.

Thanks for the test idea. Wish I would've thought of that. That makes a huge difference to have something to actually be able to test for rather than popping all the lines off and doing a valve pressure test.
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