Brake proportioning valve

[Guest]

I noticed when i got home today that my brake pedal, when pressed fairly hard, made an audible clunk noise from under the bonnet accompanied by a bump or clicky feeling through the pedal. It kind of sounds like a spring binding or something. Its there on the stroke down and also in the same place on the way up. Popped the bonnet an had a feel/listen round whilst having the brake pedal pressed an it feels and sounds like its coming from the brake proportioning valve. Apart from this the brakes appear to work normally, but i'm a wee bit dubious about giving them a good test (for obvious reasons).

Does this mean it's buggered or what? And what does a new one of these babies usually cost roughly? I just got a nice big tax bill yesterday so i'm hoping not too much :-\

[Guest]

what model?

[Guest]

1994 BG7 legacy Brighton 220

[Guest]

Check and lube pedal pivots first of all

[kamineko]

watching this thread.. i have a similar noise/clunk. i'm pretty sure its just my firewall flexing but hmm

[Guest]

Ok I'll check the pedal pivots tomorrow. I'm not sure that's the problem though as there is a definite noise coming from the proportioning valve, and when I hold it I can "feel" the noise if you know what I mean. It is a FIRM push, and only when the booster has vacuum (engine running). I can't push the pedal far enough without the engine running to create the noise/feeling. I think if you pushed that hard while driving you'd kiss the steering wheel More a holding on a hill kind of push.

It's amazing how much flex there is in the firewall though! I've never really watched the master cylinder while the pedal is being pushed hard until tonight. I can now see how a brace can make so much difference to pedal feel when you see how much movement there is. And before you say it, I checked the mounting nuts/bolts on the firewall in case it was that 8)

[Guest]

No problems in the pedal pivot area. Not an easy fix sadly :-[

[Guest loren]

I can't imagine any moving parts in a fixed pressure proportioning valve... seems more likely to be a problem elsewhere.

Are you sure you know which bit is the prop valve?

[Guest]

Yes I do know what the proportioning valve is.

Proportioning valves do contain moving parts, including a spring which sets the "crack" point. The 'crack point' is the point at which the front and rear brake system pressures change from being the same front and rear, to where (normally) the rear brake pressure increases in a smaller proportion to the front. That is, as you brake, the front and rear brake lines have the same pressure until you reach the 'crack point', at which point the rear pressure increases in proportion with the front pressure according to the bias ratio of the valve.

I've never had one fail, i didn't think they did. How ever if any one has experience with these failing is this noise/feel an indicator?

-edited

[Guest boostcut]

id be pulling the cylinder out and checking the bore and cups... also the alloy piston inside could be tipping over and causing the creak.... just my view... but yeah since this thread has turned into a slag fest please dont comment on it if all you want to do is wind people up...

[Guest]

boostcut - Do you mean the master cylinder or the proportioning valve?

[Guest boostcut]

the master cylinder... the movement in the proportioning valve will be most probably just transfering through the fluid etc...

[Guest]

Ok, another quick question. If I was to upgrade my brakes (rotor's and callipers) from the standard NA 260mm single pot , to 274mm disk with 2 pots, would I need to change the master cylinder and proportioning valve? I'm pretty sure the master cylinders are the same but I don't know about the valve.

Reason being, I found out over the weekend I have a mate who will give me some disc's and callipers off a v3 (i think) sti for free. They are the above mentioned size.

If I do, then obviously I will replace the proportioning valve with the appropriate part.

[Guest boostcut]

on the side of the cylinder it will say nabco and then like 1. 1/4 or something.. if thats the same then no need.... and i wouldnt bother about proportioning valve.... they are probably similar inside.... the only problem i have ever seen a valve give is a poor balance reading on the brake rollers at testicle station

[Guest]

Hmmm, ok I will definitely take him up on the free brake upgrade, its all four corners (i have non vented rears atm), and the front disc's are new. I might just seek a professional opinion on the proportioning valve noise feel thing, and if I need to replace it I'll use the one to match the brakes I'm putting on.

Thanks for the input boostcut.

[Guest boostcut]

thats sweet.. its hard to tell where the noise is coming from when you cant hear for yourself... hope you sort it soon mate.. cheers adam

[Swindog]

Sure the noise isnt the clips over the back of the pad moving with the pads when they grab the disc? They make a loud clicking/clunking sound.

Mine do this cos of the way i modified the pad backing but ive heard of them doin it on others.

[Guest]

Na, don't think so boss. It's definitely under the bonnet, in the master cylinder/proportioning valve region. I had my ear right in the area and felt around various components while the wife pushed the brake pedal a few times.

Is there any special procedure for bleeding the brakes if you have ABS? When I do this brake upgrade I have planned (picked up bits from my mate today) I want to replace my brake fluid. Is there some way to make the ABS pump purge the old stuff and cycle through the new fluid?

[Guest boostcut]

na just bleed it normally.... do 1 or 2 full reservoirs per wheel and it will be fine..

[Swindog]

What he said. I have same setup as you and bled a full 500ml through the system. Youd be amazed the gunk that sits in there in the last caliper. I think it worked out to be 6 full pumps per caliper to clear the entire system.