Dual Circuit Master Cylinder

Kman1600

Kman1600

Member
Hi,

I’d like to convert my Historic Rally car to a true dual circuit system but this is proving to be harder than I’d thought. I was thinking of fitting a balance bar pedal box with the cylinders point into the cab rather than through the bulk head. However on checking the rules for the sort of events I’m interested in doing this modification would carry a penalty. They are OK with converting from single to dual circuit but they draw the line at bias bar pedal boxes. I’m therefore back looking for a replacement dual circuit master cylinder that will fit in where the standard one is, has anyone got any suggestions? I realise I will probably have to fit 2 servos if the resulting pedal pressure is too high but I sort of OK with that.

Thanks

Tim
 
P6's destined for the US and certain European countries had a dual circuit set up which is a notorious nightmare. Don't copy it! I think I'd want a very good reason to depart from the standard single circuit brakes. Designing a braking circuit to get all the right cylinder sizes and servo ratios is a reasonably technical job and liable to a certain amount of trial and error. You could well finish up with a system more failure prone and less safe than the single circuit one you started with!

If properly overhauled and set up the handbrake on a P6 is reasonably effective....

Chris
 
Hi Tim,

If going for a P6 system you'll need a dedicated master that has the diaphragm valve assembly on it, a servo that does not, a second reservoir on the servo end of the system and two lenghts of vacuum hose passing under the engine with clips and fittings, a few lengths of copper pipe and connectors. That's what comes to mind. I might be able to point you to a 2nd-hand spares source in Sweden (PM me for that) and there is a lady in Canada that sells NOS components (I believe). Maybe Ian Wilson can have some used off of NADA cars.

Downsides to the dual-circuit P6 system - although mine (old car) worked well, my brakes specialist thought the slight hesitation and softish pedal I had might be due to "the way the system was designed" and the condition of all the components, in combination. It was a high-mileage car. What else may constitute a nightmare I don't really know. I overhauled the system on it and it was fine for the three years I drove it.
 
I should know better than to post unsupported opinion on here, shouldn't I Tor! Criticism of the Rover installed dual circuit set up has been threefold. First is as described by you - poor pedal feel, which must presumeably translate into some degree of non ideal performance at the limits. I think this is ample evidence of the hazards of DIY design - they probably gave it to the apprentice drawing office lad just to get it into the relevant markets! Second is poor or non existent spares availability for the Rover system. These two have lead a number of people in the US to convert from dual circuit to single circuit. Finally the Rover system as installed is supposed to be extremely difficult to fault find. There seems to be a tendency to start at the beginning and work through the system renewing things until the problem goes away rather than indentifying the problem up front.

Of course none of these criticisms need apply to a well designed modern system - but we are handicapped by not being able to change the calipers easily and by the physical layout of the pedal box and engine bay space. I just think the downsides far outweigh any potential advantage.

Chris
 
Hi,

Thanks for the replies, I’ve certainly ruled out the standard Rover split system. I did find cylinder for a Westfield with looks promising if you could attach remote reservoirs to it. Once split I could either run with 2 servos or if I could find a small enough ID cylinder maybe eating 2 weetabix each morning :)

Thanks again,

Tim
 

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That looks sorted then, good for you!

No worries Chris, I was hoping you'd return to fill in the gap... A fellow P6 owner locally also retrofitted his 1971 V8 with a single-line system - but he too has poor pedal feedback, go figure. As mentioned elsewhere my current 'S' is better but still a bit on the soft side - but it has silicone fluid in it which has that characteristic.

I'm thinking that, as the braking action is dependent on the diaphragm valve for boost, any delay or "stepping on dead rat" pedal could very easily come from it getting old?
 
I think the rover dual brake system is the same as Jaguar used on the E-type v12 models. Cant't be that bad, but a bit more complicated than the singel system. Master cylinders are available, but servos are hard to find. The calipers are the same as on the singel system models. The brakes on my car is quite good.
 
Hi
I have recently rebuilt a NADA 3500S dual line system from the ground up . It is a mickey mouse engineered plumber's night mare , a total bodge, designed to sneak the car through the US safety regulations . Any system which has around six feet of vacuum hose between the master cylinder air valve and the servo does not produce the most rapid response braking !
The master cylinder / air valve is the same as the E type , that's about the end of any resemblance between the two systems . I've also rebuilt an E type 's brakes ,the inboard rear brakes are not the easiest , but they are far less complex than the P6s.
I rallied a Volvo 122S ,{ a brick outhouse of a car }which was a contemporary of my P6 . Volvo used the same era Girling Lego kit of brake parts and managed to engineer an excellent , true dual line brake system .

I must go and lie down , I feel a fit of the wobblies coming on !!!!
Cheers
RVW
 
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