Hi,

What do you think of this, instead of two MC's on the pedal? Is it road legal?

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Not legal for IVA purposes, not too sure about legality otherwise. I expect it would invalidate the type approval, but whether that in itself is illegal I don't know.

Are they reliable?

Personally I prefer to use two m/c but I can appreciate that the restrictor valve could be useful in some racing applications.

How would you ensure that you had two independent braking circuits so that if one fails you have the backup of the other one to slow you down albeit more slowly. I wouldn't like the thought of only having one system.

You can still have two independent circuits. You are simply making one of them less effective by restricting the flow on one circuit which will transfer the pedal pressure to the other - sort of like a bias bar.

That's why I asked about reliability... If I had to install backup lines I might as well go for the two MC's, which is exactly the subject of this topic, not doing that!

AP and Tilton both make (made?) these types of proportioning valves. They are intended just to be plumbed into the rear circuit and hence can be used with tandem m/cyls or twin m/cyls.

They do work well and are reliable. The Tilton version had a lever to actuate and was used in a lot of rally cars so the driver could adjust the front rear split on a stage when going from tar to loose for example.

Under Group N regs the AP version could be used to replace the OE proportioning valve as the homologation papers simply stated at the time Brake Proportioning Valve Yes or No.

As for the quality of this one I really dont know but they are so simple (a piston with a spring behind it) that they should be difficult to make unreliable.....

Just to add some info, I run two master cylinders on mine as well as a dual head remote servo, I have a adjustable bias knob that adjusts the bar between the two mc,s.

Whilst doing an event in Corsica in October I burst a rear brake pipe on the axle, not fun as we had over 130 competitive kilometres to do. However I still had front brakes and they stopped me, but no good for braking into hairpins or fast corners, some real moments at times and my navigator mentioned we should adopt cadence braking as a matter of urgency.

But we finished and I made a new line up that evening.

So run split systems!!!

You don't need to run twin master cylinders to be safe though. A tandem master cylinder with an adjustable proportioning valve in the rear circuit is every bit as safe. I have competed on countless rallies in Gp N including World Chamionship events with this set up as have hundreds of others.

This type is not ideal in Sevenish car because the brake hydraulic pressure is so low .


If you want an adjustable brake pressure regulator valve The Fiat Ritmo/Strada or Lada Riva valve can easily be converted and is very cheap.

If you want a simple no-adjustable valve stick FWD Ford or Vauxhall Corsa valve in the rear line.


For road use use and tandem master cylinder with a small bore will give simple decent brakes with a reasonably low pedal effort ----- Fiat 124 master cylinder is a good cheap solution.


The most important thing is for road use don't fiddle with the brake bias, set it up properly so the front brakes always lock first on a good clean dry road surface and leave it at that setting.

[Edited on 2/12/10 by britishtrident]

I've search for that Fiat Strada/Ritmo brake valve but they don't seem to be adjustable by hand...