23 replies to this topic

[pikey7]

 bias_valve.jpg   98.17K   1 downloads

Well, this is the cross section. I'll have a look in a bit (got some ebay items ending), and explain what I think happens. In the mean time.......

by the way, the front just goes straight through the unit and doesn't affect the unit at all!

[Dan]

Looks to me like it is a delay valve as I thought. Is spring A really light? Pressure applied will press the outer piston away, releasing pressure against the ball bearing valve seat and allowing fluid flow to the brakes. If this is the case I always thought it would be like this just to stop the rear brakes getting full pressure early, instead bringing them up to pressure slowly so the rear don't lock up.

Are you sure there's no interaction with the front circuit? It seems a bit elaborate to run the front brakes through it as well if they do nothing to it. I always though it would vary the speed that pressure comes up in the rear circuit based on pressure in the front circuit.

Nice one.

Edited by Dan, 14 April 2006 - 07:19 PM.

[pikey7]

spring A is actually quite heavy. I wans't sure if tensioning it more would change the "swithcover" point and delay things further. Like I say though I haven't really though of it a lot, just done that diagram really!

I'm relatively sure that the fronts don't have anything to do with the rear, but I'll double check in the garage in a bit.

[the old git]

This was posted on 16VMC in a similar thread.

We did away with FAM7821 on our Racing Super Mighty Mini. The two pipes from the servo--one goes to the front subframe direct, the other, inside the car to an adjustable brake bias, lever type, and then on to the standard 'T' piece on the rear subframe as per standard fitment. Works a treat. We actually have the Race Mini MOT'd and taxed for the race season for testing purposes and on taking it for MOT the tester could not believe the high braking percentages

[sqweaka]

this is the bias valve your looking for £10 inc postage

[pikey7]

We did away with FAM7821 on our Racing Super Mighty Mini. The two pipes from the servo--one goes to the front subframe direct, the other, inside the car to an adjustable brake bias, lever type, and then on to the standard 'T' piece on the rear subframe as per standard fitment. Works a treat. We actually have the Race Mini MOT'd and taxed for the race season for testing purposes and on taking it for MOT the tester could not believe the high braking percentages

'Tis indeed a much simpler system! It's good to know someone actually has experience of doing it this way as that FAM valve looks waaaaay to complicated to mess with and be sure of the results, and the old style valve on the rear means getting mucky if it needs adjusting!

Thanks for the post!

[pikey7]

Double checked in the garage, the front circuit is independant of the rear.

Having looked at it a bit more, I'm a little stumped. When you press the pedal, the fluid must try to close the valve and the piston not allowing any fluid to flow to the brakes. I can anly assume that there must be some residual pressure from the rear system that holds open the one way valve. Then when you let off the pedal, the pressure on the MS side drops, and the whole piston moves to release the pressure at the rear. That is unless the "out" is to the master cylinder, but I'm pretty sure that bit's right! Time for another look methinks.....

[Jammy]

This maybe what you've wrote Pikey (am utterly tired so couldn't really work it out), but from reading everything I'm guessing this works a bit like a shut off valve to the rear brakes when the pedal is pressed beyond a certain point, and therefore pressure hits a threshold?

[pikey7]

Honestly, I've no idea what I wrote! I can't understand myself.....

Everytime I look at it, it confuses me more (i'm probably overanalysing it), so i'm gonna have a play with the real thing tomorrow to try to work out what it's doing!