39 replies to this topic

[Ethel]

" I was concerned about back pressure on a master cylinder piston, but when you think about it, that is exactly what happens as soon as you press the pedal so that isn't an issue on the 'passive' one."
Afraid it is, the reservoir is open to whole brake circuit with your foot off the pedal. The master cylinder piston passes the drilling to seal off the reservoir before any hydraulic pressure can be built up. Simple one way valves won't work as the fluid needs to return to release the brakes.

To do it hydraulically you'd need a tandem circuit pressure differential valve, like fitted to the first dual circuit systems 13H5848, 13H5905 or RTC2525. Alternatively, rig up a slave to push the driver's master, shouldn't be too hard with a later type horizontal master and a clutch slave. Master & slave should be as near the same bore size as possible.

Plan B would be to connect the outlet of one master into the reservoir connection of the other, you'd need one cylinder to have a suitable "high pressure" reservoir connection. I'm not sure how it'd behave if both pedals were pressed, and being linked in series would double the risk of failure.

[CLM]

Hmm Sandrail cutting brake type hydraulic arrangement. Master cylinder plumbing through master cylinder to the brake system. You would take two identical master cylinders, take one of them and remove the reservoirs and attach brake line fittings where the reservoirs used to be, take the second master and run hard lines from the outlets to the corresponding reservoir fitting on the first master. Then take lines out of that to the brakes.

When the brakes are not pressed they allow brake fluid to pass from the system to the reservoir freely, the basis for the one person bleeding systems. With it set up this way the brake master with the pass through would be the the overriding brakes and would work irregardless of how the reservoir ones were pressed.

You would likely want the reservoirs on the student side and the passthrough on the instructor side so the instructor could always override and brake and the student pressing the brake when the instructor had it pressed would not do much of anything.

NOTE: I have not done this and testing would need to prove it's reliability, but knowing the cutting brakes on my sandrail, would be the least expensive and easiest way to set it up.

Chris

P.S. Bleeding would be easy, just ignore the pass through master cylinder.

Edited by CLM, 10 November 2012 - 06:15 AM.

[tiger99]

This will not actually work. It is possible in a pumped system like some Citroens, but not in a simple hydrostatic sysytem like a Mini to do it with hydraulics alone. No arrangement of interconnected master cylinders, or for that matter, non-return valves, will ever give you what is required.

However, there is a somewhat elaborate way of making it work. I am basing this on aircraft practice, mostly medium size turboprops, where in some cases the pedals drive simple hydrostatic master cylinders, each plumbed to a slave cylinder which applies pressure directly to the proportioning valve in the pump-driven part of the system. You can't use an aircraft proportioning valve in a Mini (not a pumped system, and you would have major problems finding slave and caliper seals which were compatible with mineral oil or Skydrol), so youhave to fake the same thing with bits that you can get. You need three master cylinders, and two slaves having equal diameter and stroke. Each master cylinder is simply plumbed to its own slave, the slave having a bleed nipple of course. Both slaves are arranged to push against the third master cylinder, which is plumbed into the brakes in the usual way, but which can be located somewhere convenient, as it is not connected to the pedals. You will need a very rigid frame to mount the two slaves and the main master cylinder, and as it will probably be impossible to find small-diameter, large stroke slaves, you will need some kind of lever to adapt a larger diameter, short stroke slave to the standard master cylinder travel. It is vitally important that either slave can push the master through its entire stroke. You do not use a linkage like a balance bar in reverse, the slaves need to operate such that the one which is pushed farthest wins. I would guess that clutch slave cylinders, with a lever to step up the stroke in the correct ratio, would be the easiest things to use, as they have about the same volumetric displacement as a master cylinder. Wheel cylinders are much too small.

[Tamworthbay]

Thanks for the answers guys, lying in bed overnight I had discovered various problems with my planned system, several of which are outlined above. I have thought of a range of possible solutions from the vaguely practical to the slightly bonkers (machining up a hub with two calipers mounts to run two independent systems). The easiest at the moment looks like an arrangement of the fiddle brakes to work on both front wheels. If that isn't possible I will investigate the possibilities above. The shell is way from ready so we aren't in any rush, but I like to bounce ideas round my head for a while so when it comes to the time I know what I am doing.

[CMXCVIII]

must be a pretty common thing, i think it's a legal requirement in learner cars to have dual controls in the uk

not very commom in minis i guess but the principle is the same

Trac

It was very common indeed on minis up to about 15-20 years ago. Nowadays no-one makes one and I have completely failed to track down one. Surely someone must have one sat in a garage somewhere? I have asked bout a bespoke fitment and got price guides of approximate 2k, which is about 1.9k over our budget!

Have you tried asking 'old' driving instructors for an 'old' set of dual controls?

A minute online found both http://www.adinews.co.uk/ and http://www.ukdic.co.uk/ . I bet you wouldn't even have to pay to advertise! They have space to fill and I suspect if you told the story to their editorial staff, they would run a nice piece about your charity and the kids you are teaching and that would put the word out that you're looking for that old set of dual controls that someone has at the back of their garage.

[Tamworthbay]

must be a pretty common thing, i think it's a legal requirement in learner cars to have dual controls in the uk

not very commom in minis i guess but the principle is the same

Trac

It was very common indeed on minis up to about 15-20 years ago. Nowadays no-one makes one and I have completely failed to track down one. Surely someone must have one sat in a garage somewhere? I have asked bout a bespoke fitment and got price guides of approximate 2k, which is about 1.9k over our budget!

Have you tried asking 'old' driving instructors for an 'old' set of dual controls?

A minute online found both http://www.adinews.co.uk/ and http://www.ukdic.co.uk/ . I bet you wouldn't even have to pay to advertise! They have space to fill and I suspect if you told the story to their editorial staff, they would run a nice piece about your charity and the kids you are teaching and that would put the word out that you're looking for that old set of dual controls that someone has at the back of their garage.

Thanks for suggestion i will have a look on those. I have asked around and had a request posted on a forum and up on the walls of the local test centres. It seems that generally the cars are just sold on, usually part ex against the new car. I guess the dealers would just bin them and attempt to hide the fact they were driving school cars. There must be one sat somewhere but finding it is beating me at the moment. I keep an eye on eBay, but then who would think of using a mini for a driving school car today? So will anyone bother trying to sell one? I will keep looking but want to have another system planned in case it doesn't happen.

[matt615]

A minute online found both http://www.adinews.co.uk/ and http://www.ukdic.co.uk/ . I bet you wouldn't even have to pay to advertise! They have space to fill and I suspect if you told the story to their editorial staff, they would run a nice piece about your charity and the kids you are teaching and that would put the word out that you're looking for that old set of dual controls that someone has at the back of their garage.

Good suggestion.

Failing that, could you not fabricate your own set of dual controls? Fit another pedal box in the passenger side, and then link them link somehow link them to the main pedals?

[Tamworthbay]

A minute online found both http://www.adinews.co.uk/ and http://www.ukdic.co.uk/ . I bet you wouldn't even have to pay to advertise! They have space to fill and I suspect if you told the story to their editorial staff, they would run a nice piece about your charity and the kids you are teaching and that would put the word out that you're looking for that old set of dual controls that someone has at the back of their garage.

Good suggestion.

Failing that, could you not fabricate your own set of dual controls? Fit another pedal box in the passenger side, and then link them link somehow link them to the main pedals?

We have looked at that, but school insurance is a bit strange. We can build a car from scratch and race it with no problems, but 'modifications' to an existing one are a different matter. It may end up with us doing that and getting it signed off by someone in the know as it were. Just looking at all the options really. The issue with home fabricated stuff is how to test it for an extreme situation. By using a dual hydraulic system we would be using components that have all been proven to work, e.g master cylinder, LHD pedal box etc and it would be easier to convince them. The best solution will be to find a set of proper dual controls, but I need a backup plan in case that fails.

[racingenglishcars]

I'm thinking that the most common type of dual brake pedals is with a torsion rod from the passenger brake pedal to simply push on the driver's brake pedal. Without permanent physical contact (few mil clearance) it wouldn't even be a modification.

[MiniLandy]

If you do decide to make a mechanical setup, here's some inspiration. The principle's the same, you'd just need to keep the servo on the driver's side, and weld three tabs on the long outer tube instead of two.

As for the lathework involved in making certain parts of it, by using 27mm ID tubing you could use the standard bushes, and drill and tap both ends of 14mm bar for the central rod.

If this is something you end up looking at more closely, drop me a pm, as I'm currently doing it to my mini (like in the link above, but mounting the servo slightly further left, on the LHD brake mounts).

[Ethel]

See if you can find a scrap LHD '88 on Mini, or one that's going to be converted to RHD.

http://www.somerford...page=page&id=58

It would be easier to make the whole car LHD, or automatic.

[lapider]

dont forget youl need a dual control clutch as well

[tractor]

doesn't being able to knock it out of gear get rid of the need for a dual clutch? i thought in learner cars they just have a brake pedal on the passenger side but i might be worng.

i know i've had to resort to knocking it out of gear and the handbrake as a passenger before now

trac

[Tamworthbay]

I'm thinking that the most common type of dual brake pedals is with a torsion rod from the passenger brake pedal to simply push on the driver's brake pedal. Without permanent physical contact (few mil clearance) it wouldn't even be a modification.

That could work well, without a tunnel there is plenty of space in the front of a mini

If you do decide to make a mechanical setup, here's some inspiration. The principle's the same, you'd just need to keep the servo on the driver's side, and weld three tabs on the long outer tube instead of two.

As for the lathework involved in making certain parts of it, by using 27mm ID tubing you could use the standard bushes, and drill and tap both ends of 14mm bar for the central rod.

If this is something you end up looking at more closely, drop me a pm, as I'm currently doing it to my mini (like in the link above, but mounting the servo slightly further left, on the LHD brake mounts).

Thanks for the link, machine work is no problem, we have an ex BL toolmaker on the staff (did the tool for mk4 wings many moons ago)

See if you can find a scrap LHD '88 on Mini, or one that's going to be converted to RHD.

http://www.somerfordmini.co.uk/eshop/index.php?main_page=page&id=58

It would be easier to make the whole car LHD, or automatic.

The holes are already there, which is why I had the idea at first.

dont forget youl need a dual control clutch as well

In the OP I want all the control I can get, in the beginning at least.

[Ethel]

The holes are already there, which is why I had the idea at first.

Follow the link , if you haven't, the post '88 LHD's have a torsion bar & the master still on the right.