Got myself a full sierra cosworth back end now, and will be using sierra master cylinder, so i've got a feeling that locking up the back end wont be too hard. Question is what do we think of this brake bias valve. Pre sva it will be hidden in the tunnel, and afterwards i'll move it to be more accessible.
Opinions guys please, its a bit cheaper than willwood ones!

cant see anything chris? many peeps have sucesfully used the fiat uno bias valve, which is cheap as chips, and easy to make adjustable.





Originally posted by chris_harris_
Got myself a full sierra cosworth back end now, and will be using sierra master cylinder, so i've got a feeling that locking up the back end wont be too hard. Question is what do we think of this brake bias valve. Pre sva it will be hidden in the tunnel, and afterwards i'll move it to be more accessible.
Opinions guys please, its a bit cheaper than willwood ones!

The tunnel isn't as good a hiding place as you might think.

Just screw a Mondeo valve into the master cylinder outlet easy to take out and replace with something else post SVA --- two minutes to remove one in the scrappies but chop through the brake pipe as the tube fitting will need to be salvaged.

Here's my understanding of brake bias valves: -

It limits the "peak" pressure on the rear brakes, up until the limit the front and rear get even pressure - beyond this point only the fronts get more pressure.

With a balance bar and 2 master cylinders you get a better progressive ratio eg 60/40 front/back throughout the braking process at all pressures.

So if you just want to stop the backend locking up under heavy braking then the bias valve will do the trick. If however you want more control and everything to be nice and balanced when not braking 100% then the 2 master cylinders and balance bar thing is a better option.

My car has the bias valve (on the centre console, added post-SVA presumably). However I suspect I'm not a good enough driver to notice the advantage of the progressive nature of the balance bar approach - you may be in which case that may be a better approach.

Please someone correct me if I'm wrong - I like to learn stuff

A bias bar uses leverage to share the braking between front and rear, so you always get (say) 80/20 fr/rr regardless of pedal pressure, regardless of braking g's
On dry tarmac with good tyres 80/20 or 70/30 would be required to prevent rears locking first because of weight transfer.
Same car on ice could only brake at a low rate (say 0.1g) and the weight transfer isn't happening so static weight distribution (say 50/50) would apply. With a bias bar set to 80/20 you have 1/4 braking force on rear cf front and overall brake force must therefore be down at 37.5% LESS than what is possible.
A proportioning valve allows the brake ratio fr/rr to more closely follow the weight transfer characteristics and therefore in my opinion gives better braking in less than optimum conditions.
But it's got to be designed right!
A lot of folk think the bias bar is a better solution which production cars don't use for cost reasons: my reasoning (above) suggests this is not the case.
cheers
Bob
PS - I've

Several types of valve out there, some are simple shut off, some proportioning some have a combination of the two.

For the reasons Bob C outlined so concisely
a proper proportion valve is very good but even a simple shut off actually works pretty well for road use and is probably a lot more suited to road use than a bias peddle box.


Seems to be a macho culture thing that has grown up with a fixation on bias peddle boxes because proper racers have them, brake bias is not a thing to twiddle with on the road.

[Edited on 5/5/06 by britishtrident]

I stand corrected! And happy that I appear to have the more favourable solution

double-post

[Edited on 5/5/06 by gingerprince]

Apologies, i forgot to add this bit: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=8039649597&ssPageName=STRK:MEWA:IT
Interesting discussion then, i may just go the mondeo route to begin with then and then add one after, but this sounds like its just controlling the amount of pressure going through, it even says you can lock it off!, how do we think a willwood one would vary?

quote:

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Originally posted by chris_harris_
Apologies, i forgot to add this bit: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=8039649597&ssPageName=STRK:MEWA:IT
Interesting discussion then, i may just go the mondeo route to begin with then and then add one after, but this sounds like its just controlling the amount of pressure going through, it even says you can lock it off!, how do we think a willwood one would vary?

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Oops didn't notice that, ver goof point thanks! think i'll pay the extra then! Thanks ALL.