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Brake Proportioning Valve noise?


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6 replies to this topic

#1 Fairtax4me

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Posted 09 June 2014 - 10:14 PM

Girlfriends 95 Legacy LSi started making a weird noise today. If started out as a clicking or popping sound when the brake pedal is depressed. Only happens when the pedal is moving.
I poked around with the stethoscope and determined the noise was coming from the proportioning valve.
Pedal feel is fine but I decided to bleed the brakes to check for air. No air, but I found some nasty fluid in right rear caliper.
Now with clean fluid throughout, the clicking noise was gone, took the car for a drive. After about 20 minutes of driving here is a new noise. Kind of a humming sound. Again, coming from the proportioning valve. It's kinda like the hum sound you get from blowing across the top of a bottle.
It only makes the sound as the pedal is being depressed. Once the pedal stops the sound stops, and it does take some force on the pedal to make the sound.

The pedal feel is fine. No sinking or softness. Braking is even.

Not real sure what to think of it. Odd noise, but everything seems to work fine. Bad proportioning valve? I haven't ever heard of one going bad. Not just on a Subaru, I mean ever never.

Anybody else experienced something like this?

#2 CNY_Dave

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Posted 10 June 2014 - 09:37 AM

Small leak somewhere?



#3 Fairtax4me

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Posted 10 June 2014 - 11:37 AM

Forgot to mention that. Found no leaks.

#4 CNY_Dave

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Posted 10 June 2014 - 02:39 PM

Drum rears?

 

Maybe the rears are out of adjustment.

 

Just a wild guess though...



#5 Fairtax4me

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Posted 10 June 2014 - 05:38 PM

Disc rears. Both slide easily because I just put new pads and rotors on it 2 months ago. Cleaned and re-greased the slide pins. Had to replace one caliper because the piston was seized. The other caliper was smooth and is working normally.

What I gather from the FSM is the proportioning valve is supposed to trip at around 450 psi. Until that pressure is reached, front and rear braking pressures will be equal. After that, rear pressure is limited proportionally to the front pressure. It does this by using a dampening chamber with a diaphragm and spring. Fluid will press on the diaphragm and depress the spring, which effectively lowers the pressure going to the rear brake calipers.

So it seems to me that the proportioning valve is functioning at least somewhat normally, and what I'm hearing is the sound of the diaphragm and/or springs moving inside the valve.

If there is a leak in one of the rear lines, there will be low or no pressure in the line, and thus no actuation of the proportioning valve.

I think my next step will be to swap in another proportioning valve and see what happens.
I know the one in my 96 works, and doesn't make noise. I have new brake hoses to put on that car anyway, so ill try a switcheroo and see what I get.

#6 1 Lucky Texan

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Posted 10 June 2014 - 11:17 PM

any chance the rubber line on the new caliper is twisted or kinked?



#7 Fairtax4me

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Posted 12 June 2014 - 05:32 PM

I wish it was something that simple! I would have kicked myself and not posted anything about it! :D

As far as I can tell (without putting a $500 brake system pressure guage set on it), its working normally. It's just making noise while its compressing.
The sound hasn't changed any in the last two days. But it only happens if I really jam on the pedal now.

Gonna pull the lines off it this weekend and see if a bunch of crud comes out of it.




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