Quick question: I'm fitting rear disc brakes on my Indy. The rear calipers are from a Scorpio and use non vented discs. Front is standard Sierra calipers with vented discs. Do I HAVE to put a pressure regulating valve in the rear brake line?

No,you don't have to fit one,but if your going to use it for some serious track work I would recommend fitting a after market brake bias valve,such as the wilwood,as in wet conditions under hard braking with the standard sierra brake set up,the rears do tend to lock up before the fronts.

Choice is between balance bar + 2 master cylinders or rear brake proportioning valve. Most people use the former and it's very adjustable; you can use different bore m/cyls to increase the range. My personal opinion is that a properly set up prop. valve (e.g. the wilwood) is a better solution because it automatically compensates for surface conditions: but it's also easier to get dangerously wrong {though the SVA test would pick dangerous errors up)
A balance bar is set up to prevent the rears locking when the fronts haven't (causes an unscheduled handbrake turn!!!). Worst case for this is maximum retardation, i.e. perfect surface & good tyres. The higher rate of decelleration causes weight transfer to the front and the unweighted rears are more likely to lock. So the bias bar ends up with say70% braking effort on the front and 30% on the rear.
However when braking on a poor surface - the weight distribution stays at say 50/50. Under these conditions a 50/50 braking effort would give max possible retardation.
Lot of typing to say - in the wet I'd expect the front to lock before the rears on an SVA passing car (especially one that doesn't use a proportioning valve)!!!
cheers
Bob

Hi there

I'm building an Indy with the larger cosworth non-vented discs on the back and I have decided to fit a brake bias valve.

I got a wilwood one brand new from the US Ebay, cost £25 and included shipping from the US to the UK.

Cheers

Ian

Guess I should have mentioned I am using the standard Sierra master cylinder and will be using the car for road use mainly.
Thanks for the replies though.

I AM SHOUTING THIS YOU DONT NEED ONE

BUT i WOULD TRY AND DRIVE ROUND YOUR STREET WHEN FINISHED LAMPING THE BRAKES ON

A BIT OF WEAR REALLY HELPS AT SVA

I hear you all the way in Holland! I'll do without then (saves me some time and work too, not having to find one and put it in).

Cheers

quote:

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Originally posted by zxrlocost
I AM SHOUTING THIS YOU DONT NEED ONE

BUT i WOULD TRY AND DRIVE ROUND YOUR STREET WHEN FINISHED LAMPING THE BRAKES ON

A BIT OF WEAR REALLY HELPS AT SVA

---

That's not a shout I'd be confident about - scorpio brakes vs sierra brakes + unknown weight distribution puts plenty variables in the mix. And bear in mind if it IS too much on the rear, you'll find out while panicking on a good surface... for maximum thrills & spills!!!
I'd respectfully suggest that brakes are something that DO need to be got right....
just a word of caution ;^)
Bob

Locking the rears up before the fronts in an emmergency situtation is a very effective way of commiting sucide a Locost will swap ends faster than the blink of an eye.

And if you think it "won't happen to me" recently I was confronted with an old woman in a Micra comming up the wrong way on the High Blantyre slip road off the East Kilbride expressway --- it was a blind corner and wet --- most unfunny --- boy was I glad of having ABS on the 75 which allowed me to steer round her.

Fiat Uno valve is cheap and easy to use --

Okay, I seem to be getting mixed messages here, but with a majority leaning towards a bias valve. So I guess I should look into one.
In earlier posts usually the Fiat Uno valve is mentioned. There is a thread somewhere where someone stated you don't need a stop bolt on it, because the more the operating rod comes out, the more the pressure is reduced. Anyone know if that is true?

Also I've heard mention of the Fiesta or Mondeo type that just screws into the outlet of the M/C. Anuone used that to good effect?

My main aim is to get a setup that will get me trough SVA.

Again,you don't need to have a bias valve fitted to get through SVA.The standard type of bias valve thats is used,ie the uno type valve,will have no effect on the vehicle brakes while the vehicle is stationary,these valves only operate when the vehicle starts decelerate,only aftermarket type valves,ie wilwood effect the brakes when stationary in addition to when the vehicle is in motion.I would again advise fitting a aftermarket one for reasons that I previously mentioned in my earlier post