rear 'brake regulator'

[jimnielsen]

On the rear braking system is a device (called in the manual a 'brake regulator) that connects to the anti roll bar via a spring. Obviously this is supposed to vary the braking force supplied to the rear brakes dependent on the passenger load in the rear. Questions...

1. how does it interact with the ABS system? why can't the ABS system do without this thing - because surely a lightly loaded rear would make the brakes try to lock - which the ABS system would try to prevent??

2. how best to configure this device for a racecar that has no rear seats and is always trying to use maximum braking effort?

Thanks - jimn~

[wrinx]

I've no idea how it interacts with the ABS system...not sure it does directly. I would have thought the proportioning valve is separate and the ABS just detects a locked wheels. Or have I misunderstood you?

If you're experiencing locked rears or trigger happy ABS have you thought about using an aftermarket bias valve, where you can adjust the amount of front to rear braking manually?

Iirc they are illegal on road cars in the UK, but as yours is a track only toy...

wrinx

[wrinx]

...failing that, you could experiment with weaker springs on the valve to provide less effort on the rear

wrinx

[Steve Webb]

The rear bias valve has no direct connection to the ABS system, as the rear of the car is loaded up and the suspension droops, the rear ARB twists, which pulls on the spring and bias valve which in turn allows more rear brake bias.
The connection to the rear ARB is via a collar which can be rotated on the ARB allowing you to change the amount of rear bias.
If the rears are locking up/triggering the ABS, you might want to try backing the valve all the way off, or removing the connection to the ARB so that you have minimum rear brake bias all the time.

Thats if I've understood your post Jim.

[Evodelta]

?

Iirc they are illegal on road cars in the UK.

wrinx

No that's not true.


I can only speak of my own experience: I removed the whole lot, brake valve, ABS, piping - the lot. The ABS pump weighs a fair bit, so a good saving was to be had there.

Then I started again, new pipes straight from the brake cylinder to the fronts and through the car to the rears via an adjustable bias valve. It's not as good as a proper pedal box, but it was cheap enough to do.

[jimnielsen]

yes, you have understood - I may try this - removing the connection between the anti roll bar and the 'regulator' ...


jimn~

[Evodelta]

There are some schools of thought that say because your front wheels are connected to the rears you should be able to employ bigger braking effect at the rear than a 2wd car. Not sure myself yet though.

[j1v]

Then I started again, new pipes straight from the brake cylinder to the fronts and through the car to the rears via an adjustable bias valve. It's not as good as a proper pedal box, but it was cheap enough to do.

http://picasaweb.google.com/jivco.sh...45058054862530

Here is what I got for my other project, not that expensive, ~180 pounds ... still not in the car, and can't share any experience on this

[Evodelta]

Ooh, that's nice! Is it floor mounted or bulkhead mounted? Can I ask where from?

[j1v]

http://compbrake.co.uk/brake_p12.htm

[na15575]

http://briefcases.pathfinder.gr/zoom...s/29645/606833
i have this picture for the bias ajust the system is the same like all 155's

nikos

[na15575]

I thing as much weight so much brake power you have to the rear I adjust it little stronger 5kg and then 1mm more I have try it in a track day and when I hit the brakes little hard and the car is in a little turn the back goes like a handbrake effect

nikos

[na15575]

see this pdf at 57 page

http://www.berlinasportivo.com/Techn...inclBrakes.pdf

[jimnielsen]

yes, I have access to the manuals - and I understand the standard way of adjusting the system. What I am interested in is how the system should be adjusted for a track car that has no back seats (and no passengers) and is always trying to stop as hard as possible. The choices would seem to be either (1). connect up a stiffer spring and use even more than 5Kg as a 'set-weight' or (2). remove the spring entirely. From what I have read I am thinking that option (2) is the most likely to work.

cheers, jim.

[na15575]

i thing that if you remove the spring the presure to the rear brakes is going to be lower.
and you are not going to brake with the rear brakes at all then you are stoping only with the front
is this that you want?
i thing that if you set it to 5kg is going to be fine remember the car must be in flat and all the weight of the car on the wheels .
if you make it stiffer then when you are braking the rear wheels is going to block and it is going to be like you are using the handbrake.
i have try it
the best solution is this one
set a weight of 5 kg give 1mm more and thats it you are taking the best of this system
Nikos

[cuore_sportivo_155]

yes, I have access to the manuals - and I understand the standard way of adjusting the system. What I am interested in is how the system should be adjusted for a track car that has no back seats (and no passengers) and is always trying to stop as hard as possible. The choices would seem to be either (1). connect up a stiffer spring and use even more than 5Kg as a 'set-weight' or (2). remove the spring entirely. From what I have read I am thinking that option (2) is the most likely to work.

cheers, jim.

(2) will give nearly no effort to the rear brakes.

As i understand it you want max breaking effort without locking, and have severely reduced the weight on the back wheels? The spring is there to compensate for brake bias adjustment should the back end be loaded more, or less. When braking on track this will be less than standing still anyway. On the other hand, the rear of the Q4 is heavier than the FWD version, even when stripped out

Are you sure it's the back wheels locking up? Don't you have the big brakes on the front? That would mean you need more bias to the back.

I would keep the spring, and start off with a fairly high weight (like 10kg) and give that a go. if you are sure the rears are locking up first, reduce the weight, otherwise increase the weight till you get a nice balance... my fwd car uses 10kg aswell, but still has the back seat and carpet in it. the boot is emptied to the metal though...

[jimnielsen]

OK! I'll give the 10Kg option with spring a go! I don't have any locking problems - just want to set it up for the track after having put on the new anti roll bar.

jimn~

[JumboUK]

What would happen if you changed the spring for a non-elastic wire?

[cuore_sportivo_155]

you can't adjust the valve with a solid wire, the spring and the weight must form an equilibrium...

provided the valve magically gets adjusted properly, the effects of loading unloading will provoke much more dramatic reactions...