diagonal brake lines--> why???

[touge_ae101]

so i'm looking at re-routing all my brake hardlines so i run a simple front-rear split to allow a proportioning valve to be placed in line in the dash somewhere.

so what is the actual advantage of diagonal brake lines? have had a few guesses but i'm really not sure why most modern-ish cars have them.

i know a lot of fwd race cars run a split braking system and seem to brake pretty well.

GO!

[2LTR Rona]

diagonal braking - so the average muppet on the road has more chance of keeping the vehicle in a straight line under heavy braking conditions i.e. standing on the brakes big time

If it was front or rear biased then the average muppet could get in to a lot of trouble very quickly i.e. rears locking up, spin etc etc

race cars arent usually driven by muppets, although there are exceptions of course, so you can start to play around with routing, bias etc

[touge_ae101]

thanks for that - that was my line of thinking as well.

still weighing it up as plans are for doing the targa at some stage where the car needs to be super forgiving.

does anyone know where to get a 10 or 20% reducing valve to fit into a brake line?

[d1 mule]

get a wilwood etc one on a dial, infinitely adjustable like that

[touge_ae101]

get a wilwood etc one on a dial, infinitely adjustable like that

got one sitting here, problem is it still leaves you with too much rear brake as it will only reduce up to 57% which will give adjustment between 50/50 and 78.5/21.5?? i want to be able to adjust between say 60/40 and 80/20 so a 10-15% inline reducer will give the wilwood valve a bit the adjustment in the range i want. also not quite as simple as that i think as different sized pistons (and number of pistons) front and rear require different amounts of fluid.

but still weighing it up. kinda confusing myself i'm just going off what i've read and trying to figure it out.

also has anyone got experience getting a car road legal with an adjustable valve? need to do recert at some stage and my understanding is that you just need to have it unable to be adjusted while on the road. was thinking of making a cover that screws in over the knob so can't be touched while on the road while when i'm on the track i'll just take it off so i can adjust it at arms length.

[Malcolm]

Diagonal systems are a safety feature, not an anti-muppetry device. Your bias is still affected by the relative sizing of your calipers and rotors, you just typically have equal line pressures.

So anyway, diagonally plumbed systems mean that if you have a failure in a line or seal in one circuit, you still have a moderately stable brake system, with braking on a diagonal pair of wheels. If the system were split front to rear you end up with much less stability if you lose brakes at one end

[Distrb]

also has anyone got experience getting a car road legal with an adjustable valve?

yes

need to do recert at some stage and my understanding is that you just need to have it unable to be adjusted while on the road.

your understanding is correct

was thinking of making a cover that screws in over the knob so can't be touched while on the road while when i'm on the track i'll just take it off so i can adjust it at arms length.

thats exactly what i do. just bent up a piece of alloy that bends over the knob and is bolted using the same bolts the proportioning valve uses to mount to my handbrake lever.

[edit - i'll see if i can find the picture of my solution later]

[touge_ae101]

awesome thanks man

[Mr Revhead]

Diagonal systems are a safety feature, not an anti-muppetry device. Your bias is still affected by the relative sizing of your calipers and rotors, you just typically have equal line pressures.

So anyway, diagonally plumbed systems mean that if you have a failure in a line or seal in one circuit, you still have a moderately stable brake system, with braking on a diagonal pair of wheels. If the system were split front to rear you end up with much less stability if you lose brakes at one end

QFT

[Leon]

still weighing it up as plans are for doing the targa at some stage where the car needs to be super forgiving.

Start robbing banks now.

[KinLoud]

Yeah, many rwd cars came out with F/R brake systems.

About the time fwd cars became common many manufacturers started to put diagonal brake systems in their cars. Theory is that if you lose one circuit the car will be easier to stop than if only the rear brakes worked (recall when your passenger pulled on the handbrake for a "laugh")

Diagonal brake systems have a bias valve. It has 2 lines in - one from each part of the brake master. And 2 lines out - to the left and right rear brake caliper/cylinder.

If you are redoing your brakes...
Work out the piston area for the front and rear calipers.
Try to keep the same proportion of piston area for the new calipers.
Maybe try for a bit (guessing 10 to 20%) more piston area at the front as you will need a bit more front bias with grippier tyres.

Make sure you pull the pistons out of the caliper to measure the diameter (so you can work out area) especially the rear ones, as the rubber dust seal can hide the full diameter - causing miscalculation (been there, done that)

Also consider the extra leverage a bigger disk diameter creates... This has a similar effect on bias to bigger piston area.

Try to get the bias fairly correct so the adjustable bias valve is for fine tuning, not fixing a big problem!

Good luck

Ken

[neo]

I dont know the extent of how much your changing things,

I simply routed the pipe thats closest to the firewall to the front brakes, and the pipe thats furthest away from the pedal via a willwood prop. valve to the rear brakes. Appears to work ok - can make the car behave differently under braking with the flick of the knob.

For cert I had to cover the valve so 'passengers couldnt fiddle with it'

Brake line spagetti on the firewall -orgional pipes still exist as the back-up plan should it not work was to revert to factory..


Can just see the prop. value and el-horo piping in this pic