[burls]

I was thinking I could modify a sierra Brake proportioning valve to be adjustable. I have one pulled apart and it looks quite different from what I expected.

Does anyone have a schematic for these to help me understand the flow.

The theory is if I can organise a way to make this adjustable I wont need to buy and plum in another component. It will also look original

Oh and the answer is - cos I can so dont ask

[Jezza86]

adjustable as in from the cab?

[burls]

no as in adjustable for rear disc set up

[droverdave]

I have a Holden drover workshop manual at home (paper copy, as purchased from holden), and i thought it had a pretty good diagram in it? its the green writing one that i think is uploaded where all those other suzuki manuals are.

Isn't a standalone brake proportioning valve just an orifice for the fluid to go through?

[burls]

No its a bit different to that, I'll try and load a piccie of it pulled apart.

[burls]

whats going on I cant add a photo now

[burls]

This is the valve pulled down

From what I can work out fluid goes in the port at the right lower(with the arrow in) and out to the rear brake through the upper (arrow out) port

When the pressure over comes the spring the blue valve moves to the left opening up the return port

My thoughts are that I can reduce the tension on this spring and that will reduce the rear braking

[want33s]

That isn't a proportioning valve, it is a residual pressure valve for the drum brakes.
Most cars have it built into the master cylinder but suzuki do things a bit differently.
When fitting rear discs to a drum rear car the residual valve need to be removed completely.
To maintain a 60/40 front to rear brake bias you fit a brake proportioning valve. I bought mine from wilwood.
They are legal as long as it isn't mounted within reach of the driver.

[burls]

agreed but being a suzuki drivers by nature we are tightarses

A wilwood valve is about 80 or 90 bucks plus postage and then there is the plumbing

So i was thinking I should be able to mod this easily enough and therefore would not have to change any plumbing etc etc. As it turns out it is a bit more complicated but I recon still doable.

Anyone got any thoughts on how we can accomplish this

[fordem]

Let me the devil's advocate - does that valve body take a third pipe on the bottom, just to the right of the bleed nipple, and if it does, was that pipe connected to the front brake circuit?

If I'm right about that, then it is a proportioning valve and it varies the rear cut off pressure based on the front circuit pressures - the more pressure in the front circuit, the faster the stop, the more the weight transfers forward off the rear wheels, the more likely they are to lock - unless rear circuit pressure is reduced

[burls]

so fordem yes it does have the return line

so how can I modify this to either be adjustable or change the preset pressure

[JrZook]

Make a longer bolt cap into it with a lock nut and cut a bit off the spring. Then you should be able to adjust the preload on it.

[burls]

Yeah I thought of that but the black sleeve has a seal at each end so it is there for some reason

If I could work out how it flows then I think I can sort out an adjuster of some sort

[UBZ]

the black sleeve is a hydraulic piston .
the fluid pressure from from front break circuit acts on the piston and allows the blue valve to open under spring pressure , changing the proportioning to the rear brake circuit .

block off the pipe from the front break circuit and do this to make it adjustable

JrZook wrote:

Make a longer bolt cap into it with a lock nut and cut a bit off the spring. Then you should be able to adjust the preload on it.

the residual valve is on the master cylinder , under the rear circuit outlet pipe , or at least it has been on all the rear brake conversions i have done

[burls]

What I can work out from what has been said and what I have researched is the Front brake pressure is sent to the P&B valve is a control pressure to operate the Black sleeve. The rear pressure overcomes the spring tension to open the blue valve to allow pressure to the rear brakes.

If this is correct then I could:

A. as has been mentioned replace the end cap with an adjustable cap that I can wind in or out, which should in turn adjust the pressure at which the blue valve opens and thus the rear brake pressure.

B. block off the control pressure line completely and do something??? not sure yet

Does this all make sense and is it correct??