Brake pressure proportional valve

[nicholas garn]

Hi guys, I'v read alot on the forum on this subject but didn't find an end solution. The IVA states that:
Note 4: Hydraulic valves that only operate automatically and react to vehicle loading or braking forces are permitted (Load Sensing and Gravity valves) Manually adjusted valves (other than to permit presetting the automatic function of a valve) are not permitted to be fitted even if they are rendered un-adjustable.

I'm using disk brakes all round so has anyone else used a proportional (bias) valve to stop the rear wheels locking up before the front? I understand the reason for using an adjustable valve but the IVA have seemed to made life a little difficult

Any help on this as i'm starting to assemble my brake system this week.

[flyerncle]

Inline non adjustable valve fitted in rear feed line,its been discussed on here somewhere and I suggested the ones in the rear brake circuit from either a mondeo or corsa.Corsa one's are found near the battery.

[nicholas garn]

Thanks flyerncle, I read that one and I've seen the photo. Just woundering if they will work well on the roadster because it weighs a lot less than the production cars that are supplying the valve.

Has any one used one of these valves and passed the IVA?

[Wynand]

Why not simply install a balance/bias bar on the brake pedal?

I prefer two master cylinders and should one fail in an emergency stop, the other will still function and some braking happening.

Then again, I think we are lucky in South Africa not having all these laws you guys have to abide to. No emission controls and funny stuff in the exhaust for starters

[nicholas garn]

Hi Wynand, thanks for your reply. I'm using the same pedal box as in the book using the sierra master cylinder as i'm trying to keep the price down, and it was a joy to build.

[Enoch]

Ok, here is my attempt at a definitive answer. Adjustable brake proportioning valves are not allowed by IVA. You may get away with an adjustable valve that is locked up in a way that it can't be adjusted once set - eg welded up.
Early non ABS sierras had a valve in the rear brake line that stopped the rears locking under heavy braking. The valve is an inertia device - it has a ball in it that closes off the port if the rate of retardation is high enough. The valve operation can be adjusted by altering the angle at which it sits - the steeper the angle the more retardation is required to make the ball travel up the valve and shut the rear brake line off.
I fitted one to my last buid (Robin Hood 2B) it passed SVA fine, I have fitted one the same to my roadster. I have not taken it through IVA yet but have confirmed that if I stamp on the brakes the fronts lock first so it should be fine.
Hope that helps, if you need to see photos and further details have a look at www.deepfolly.co.uk
Enoch

[nicholas garn]

Hi Enoch, Thanks for the reply. The photos are great and have aswered a few more questions, good example of how to position and run the brake lines.

[Enoch]

Hi Nicholas, haviing reread my posting I would like to clarify that the early Sierras had a limiting valve rather than a proportioning valve - the difference being that the limiting valve only comes in to operation at a point where the rears will lock up. A proportioning valve works throughout the barking range, it is not allowed under IVA rules as it can be adjusted after the test and materially affect the brake balance. Some centres have allowed ones that have been welded up but I think they have stopped that now.
Best and all that,
Enoch

[flyerncle]

I hope I am right in what I am typing,the valves suggested have nothing to do with weight and only restrict the flow and are not adjustable.As Enoch suggested the Sierra valve may meet your needs and has been tried and tested on a kit car.
When you have a car that can be driven find a local friendly MOT station and roller test the brakes it will give you some idea of the forces and split front to rear,ideally 60/40.

[mr henderson]

Originally Posted by flyerncle

When you have a car that can be driven find a local friendly MOT station and roller test the brakes it will give you some idea of the forces and split front to rear,ideally 60/40.

Certainly a good idea, but don't be disappointed if you do this, and still fail the IVA test, because the IVA test is carried out at various different brake pedal pressues, and it's perfectly possible to have a car pass on max pressure, only to fail at lower pressures (happened to me recently with a Viento).

One thing is vital, use good pads at the front (mintex) and make sure they are bedded in as far as possible by driving to the IVA test and any other bits of driving and braking you can do.