2 replies to this topic

[matthew_leech]

Hi there, I have a 79 clubman estate.

The braking system is a diagonal split set up but with 7.5 cooper S disks.

The brakes have never had my full confidence, the car always pulls slightly and one back wheel often locks up, which is rather alarming when driving spiritedly.

I have leant today this diagonal split is not all that great, what system do people reccomend?

Signal system

Dual?

And what parts are needed for each, I would like to have an adjustable brake bias too?


Thanks for any advice

Matt

[KernowCooper]

I have a 1980 and its a front / rear system on that why your earlier car had that system is beyond me? I also have the Cooper 7.5 disc setup with a remote servo as per the innocenti, and I can stand it on its nose if needed. I have the pressure reduction valve as per standard for the year on the right hand side above the clutch housing on the bulkhead. Obviously if you dont have the pressure valve you will need one and a replumb of some brake pipes.

 

Update

Just checked my W/S Manuals and it appears the very early cars had a diagonal split system

 

On early
dual circuit systems a diagonal split is used,
each circuit supplying one front and one
diagonally opposite rear brake. Later versions
employ a front-to-rear split whereby both front
and both rear brakes are operated by a
separate hydraulic circuit.

 

A pressure
differential warning actuator is fitted to certain
models to inform the driver of a hydraulic circuit
failure via an illuminated warning light, and also
to restrict the flow of hydraulic fluid into the
failed circuit. This unit is either mounted
separately on the engine compartment
bulkhead, or incorporated in the master
cylinder.

Edited by KernowCooper, 05 May 2014 - 09:52 PM.

[tiger99]

You are legally required on a car of that age to have a dual system, therefore front/rear split is the only reasonable way to go. If you go for a standard system you will need a PRV, but don't use a PDWA as they actually cause subtle safety problems themselves. You should properly wire the float switch in the new reservoir to the low fluid warning light. I am not sure if you require the test switch in a car of that year, so best fit it to avoid any difficulty at MOT time, although, as I have said previously, it does nothing at all for safety.

 

You CAN NOT legally have adjustable brake bias for road use, and as absolutely NONE of the aftermarket adjustable valves, being of US origin and the subject of much ill-informed hype, have the correct characteristics anyway, not being able to have it is no great loss. They are SOFT LIMITING valves, not the same thing. The balance could, at a pinch, be set by changing the rear wheel cylinder diameters, or, if you could get the correct parts (you can't, as far as I know), by changing the spring in the PRV. There is only a small margin between having dangerous rear brakes, which lock prematurely, and insufficient brake efficienct to pass the MOT, so the scope for adjustment is minimal. A true PROPORTIONING valve, which is what you would need, cannot exist in a hydrostatic system, as it necessarily involves a significant leakage of fluid back to the reservoir. It can exist in a "powered" system, i.e. pump-driven like certain Citroens, but I suspect that you don't want to install such a system, and solve all the serious safety problems that would arise in adapting it to the Mini.

 

There was an adjustable limiting valve that did work correctly, but is illegal in a later car which needs a twin circuit system, because it can't give full rear braking following a failure of the front circuit. That was just a modified rear-subframe mounted limiting valve, of the original type, and it was ok, actually rather good, within the limitations of the single line system. It was a HARD LIMITING valve, quite different again....

 

The best, and safest, way of adjusting brake balance, which does give the optimal proportioning action, is twin master cylinders and a balance bar. Whether you will get that through MOT I don't know, as it seems to be illegal, but from what date I can't tell. But it is correct as far as the engineering and functionality are concerned, if done correctly. There is not a lot of room in a Mini for that setup, and it really does need to be solidly engineered. There is no scope whatsoever for cutting metal out of the crossmember or bulkhead to create accessibility. I would be thinking about using a servo type pedal and linkage, and mounting the master cylinders horizontally, to avoid bulkhead butchery, but it really does need to be very strong and incapable of failure, as a broken pedal or linkage tends to be fatal. Having said that, I really do think that the balance bar method is what you are going to need, if you need balance adjustemnt at all, and with that you don't, indeed can't, use the PRV, so it ends up not being quite as complex as some options.

 

Whatever you do, I strongly suggest consulting your insurers before doing anything. All changes to the brake system affect the risk, and thus are an easy excuse for them to refuse a claim, even if it is entirely unrelated.

 

Oh, and please don't wipe out the gain in safety that you get from a new brake system by using copper pipework. Cunifer, aka Copper-nickel alloy C70600, approved to  ASTM B466, ISO 4038 and  SAE J1047, is the only sensible way to go. The copper pipe sold as "brake pipe" isn't, and its sale is fraudulent, because there is no standard for copper brake pipe. The crooks and spivs sometimes quote a BS standard, but not only is that standard obsolete, but it relates to "copper pipe for general use", not vehicle brake systems. The BS has nothing to say about the most critical requirement, fatigue strength.

 

But before you try balance bars or whatever, why not just put the car into the standard dual-line configuration and see how it drives and brakes? You may not need to do any more. The links below will point you towards what is standard. You will need a later master cylinder, due to unavailability of the older ones, but that makes no functional difference, but check the threads in the ports!

 

http://www.somerford...page=page&id=65 (pipework, PRV etc)

http://www.somerford...page=page&id=60 (rear wheel cylinder options)

http://www.somerford...page=page&id=57 (master cylinders and pedals)