Brake bias valve

[Saint AAI]

Not sure, but think my rear bias valve is not doing anything. Instead of spending £140 on a new one that doesn't come with a spring can I not just fit a manual one like THIS ONE? (http://cgi.ebay.co.uk/Brake-Bias-Proportioning-Valve-RACE-RALLY-Kit-Car-knob_W0QQitemZ290369760339QQcmdZViewItemQQptZUK_Ca rsParts_Vehicles_CarParts_SM?hash=item439b62ec53) Would be cheaper even after re-routing some brake lines.
Regards, Shane.

[phase i 16 v turbo]

I think one on ebay is a brake bias valve and one on a R5 is a brake compensator.

[Saint AAI]

Is that not the same thing? I know the standard one changes the rear bias with a spring operating a lever, but the car will never have anyone in the back or anything put in the back and will mostly be used on track so was thinking swap it out for a munually adjustable one rather than a self adjusting.

[Andrew Cooke]

the GTT has a diagonal split, that valve is for a single rear circuit

[Thundercat]

Hi, i'm also on this route with track car build, intending to join front to rear pipes together so to fit brake bias valve. then spliting pipes after to each rear calipers. Anyone done this or any other ideas

[Alastair]

You should keep your eye on this thread guys..

http://www.rtoc.org/boards/showthread.php?p=113874#post113874

should give you some advice.:agree:

[Saint AAI]

Thanks for that, this is what I was after. So would I be right in thinking that if you got a leak in a standard setup, you would still have braking to two opposite corners such as nsfront and osrear?? And so if I change the lines from the cylinder to as shown in the diagram from the link I would have a front/rear split instead and could run a single bias valve to reduce rear braking? I will be retaining the OE handbrake for the time being. If this is correct will it still pass an MOT assuming they even notice its been changed??

[Alastair]

Thanks for that, this is what I was after. So would I be right in thinking that if you got a leak in a standard setup, you would still have braking to two opposite corners such as nsfront and osrear?? And so if I change the lines from the cylinder to as shown in the diagram from the link I would have a front/rear split instead and could run a single bias valve to reduce rear braking? I will be retaining the OE handbrake for the time being. If this is correct will it still pass an MOT assuming they even notice its been changed??

Correct.:agree: Unless there is somthing Andrew Cooke / another member knows about the master cylinder design that i dont? I am sure Andrew will be online over the next few days to confirm.

[Andrew Cooke]

Correct.:agree: Unless there is somthing Andrew Cooke / another member knows about the master cylinder design that i dont? I am sure Andrew will be online over the next few days to confirm.

I'd think that there is a fair possibility that you will end up with no brakes doing this (I've seen Matt5's comment in the other thread, so I'm a bit confused). As far as I know the 2 master cylinder pistons are mechanically linked, and expect to flow similar volumes of fluid, if that's the case the difference in fluid volumes between the front and rear brakes will stop the fronts working.

I'm guessing a bit here, I've not stripped the master cylinder to see how it works.

[Andrew Cooke]

I found this nice link:

http://www.tegger.com/hondafaq/mastercylinderreplace/howworks.html

I'll sit down and consider what it all means :)

[Andrew Cooke]

I've had a read, and what I wrote before is almost complete drivel :D

however, there is an associated risk. The front brakes have over 2.5 times the piston area of the rears, so require a corresponding amount of extra fluid to operate. Actually, it's worse than that as the rear circuit locks off at about 17 bar, the fronts will see a chunk more than that. Lets guess that the fronts need 3 times the fluid of the rears.

Normally each half of the piston supplies one front and one rear cylinder, call that 4 units of fluid (3F + 1R).

If you swap the split around the front half will be supplying 6 units (3F + 3F), or an extra 50%.

If you look at the picture it's clear that the half cylinder can only supply so much fluid before the piston bottoms out. When that happens you won't get any more braking, even though the pedal is only half way to the floor.

I have no idea how much fluid half a brake cylinder can pump, I have no idea how much the pedal will go off as it gets hot. I do know that I wouldn't want to find out the hard way.