Brake BIAS Valve

[stradlater]

Did a bit of a searching and can't really find the exact answer to what I was looking for.

I need a brake BIAS valve for my car now, because the backs have way too much bias.

I've been told that there is a difference between a BIAS valve and a PROPORTIONING valve.

I've been told I need a BIAS valve. But all I can find on the online stores is proportioning valves.

A) What's the difference

B) To adjust front/rear bias, what do I really need?

C) What actual units have people used?

[Beserker99]

Heya, here's what I know from when I was learing about them myself

A) I believe they are the same, just called different names. Because in the end they, both distribute fluid to your brakes to contriol the braking bias of the car.

B) You'll need an adjustable brake bias adjuster. For this you need the unit and then install it to your existing car, removing the original brake proportional valve.

Here's a small tutorial I found that might explain things further:
http://www.flyinmiata.com/support/in...ning_valve.pdf

C) I heard the walbro units are pretty good, but that's mainly from all the sites I found to have used them in their tutorials.

Hope it helps

[YLD-16L]

A) As said above I think they are the same thing but just called different names (could be wrong though??).

B) My engineers report states that my car is approved and fitted with a brake proportioning valve.

C) My last car was fitted with a Wilwood valve, my current car is fitted with a 'Speedway' brand valve. Both did the job they were meant to. The rears were locking well before the fronts and the adjustable proportioning valve was used to correct this.

In order for this to be approved by the engineer the car had to undergo a brake test, the proportioning valve adjusted correctly and then the adjustment mechanism was removed (cut off) rendering the valve no longer "adjustable".

[stradlater]

Meh, Engineer shmengineer.... I'm not worried about that bit. :-)

[Jonny Rochester]

The valve is in line with the rear brake system only. So it is not so much a proportioning valve as a pressure limiting valve, sort of.

But thinking about it more, it is a proportioning valve. Because the output to the rear brakes is a fraction of the master pressure. And master pressure is the same as what the front brakes see.

But in a factory car the graph of master cyl pressure v rear brake pressure is not linear. Some factory service manuals show a graph. The graph is a curve, and towards the top the rear brake pressure is limited to a maximum.

I suspect that a aftermarket valve is either a linear proportioning valve, or a max pressure limiting valve. I am not sure.

[stradlater]

Ah, gotcha. I hope it's a linear proportioning valve, that makes far more sense than a max pressure limiting valve.

I've seen those valves, and they are different.

[*rivmasta*]

There are differences between a Bias Adjuster and a Proportioning Valve!!!!

1 - Bias adjuster works like this.
A dial spun on the dash twists a rod which is the pivot bar for the brake master cylinders. As the rod twists it allow either the front or rear m.c. to start applying hydrolic pressure earlier.

To do this you need new pedals, twin mcs and the bias adjuster. goood bucks, but reliable and you're not reducing brake pressure anywhere in the system - what is taken from the rear is given to the front.

2 - Proportioning valve works by reducing the pressure on a specific brake line as you move a lever. much easier to put in, much less $$$, but not quite as effective.

[merc-blue]

It more a conflict of 2 terms being used to describe the same thing,
Rivmasta is starting on another thing
A proportioning and bias "VALVE" is the same thing just limits flow to rears (which increases to teh front), changes the ratio of braking pressure to front rear

Rivmasta is talking about " BIAS ADJUSTERS" for aftermarket dual MC systems like a tilton. that uses seperate MC for front and rear and the actual imput into the MCs are changed but adjusting a rod

any of the valves put out by a brake company like willwood, tilton, AP, brembo etc are fine

[Hen]

A good (though long) article on porportioning valves.

Hen

[TA22 1MZ]

Heya, here's what I know from when I was learing about them myself

A) I believe they are the same, just called different names. Because in the end they, both distribute fluid to your brakes to contriol the braking bias of the car.

B) You'll need an adjustable brake bias adjuster. For this you need the unit and then install it to your existing car, removing the original brake proportional valve.

Here's a small tutorial I found that might explain things further:
http://www.flyinmiata.com/support/in...ning_valve.pdf

C) I heard the walbro units are pretty good, but that's mainly from all the sites I found to have used them in their tutorials.

Hope it helps

I experienced the same issue when upgrading my front calipers to 4 spots.

First of all I had to use a 1" master cylinder to flow enough fluid, because the pedal was almost hitting the floor. Once that was fixed, the rears were locking up way before the fronts, so I bought a Wilwood proportioning valve, put it in the rear line and adjusted it up. Results were awesome!

However, what I wanted to point out was, don't take out the factory valve or you will be defeating the purpose of putting the adjustable item in. I made this mistake initially and replaced it with the adjustable Wilwood valve and it totally worsened the issue.

Note to self, leave factory valve and add in the adjustable proportioning valve

[stradlater]

Ah, gotcha guys. THanks for all your input, that's really assisted in things.

I bought a Wilwood Adjustable proportioning valve, which will limit the flow to the rears.

For me it's not so much an issue of upgrading the size of the front brakes (I haven't really done this) it was more that I've added more line and the bore size of this line locker has changed the flow dynamics (I think).

Hopefully things will get sorted out with the new vavle.

[mrshin]

Sure it's been bled properly and doesn't have any air caught in there?

[allencr]

added more line and the bore size of this line locker has changed the flow dynamics

I really doubt that!!
The rears lockup too soon and they didn't before, right?
Before what?? Line size & length would make near zero difference, so it has to be something else - different friction material or different size pistons on either end, not the MC piston, and that's all that would do it, except having a proportioning/limiting valve that stopped working.

[stradlater]

Just to follow up on this one, got the car back from ABS today. They installed the bias valve, and now the brakes appear to work fine, however the pedal feels extremely hard.

Any suggestions on why that might be?

[Jonny Rochester]

Well... you still havn't told us what brakes or MC you have.