17 replies to this topic

[Swarley]

Good evening all. I've just fitted Metro 8.4 Discs and was curious if anyone has considered using their original front twin leading shoe setup on the rear.

I would assume it's just a matter of rigging up a handbrake mechanism and modifying the front backing plates to match the mounting points of rear trailing arms. Then increasing fluid flow to compensate for the extra cylinder and fitting a regulator valve to prevent lock up.

I'm guessing that I'm missing something obvious though considering I'm having trouble finding any other posts concerning this.

Any info is appreciated
Cheers

[Tamworthbay]

The rear brakes do very little work so it wouldn't be worth the effort. The standard rears are more than up to the job. It's an interesting idea but you would be doing it 'for the hell of it' rather than any practical gain.

[Swarley]

I've got a few days off so I might give it a crack. I've got a couple of spare backing plates and fresh parts to rebuild both front and back.

I guess it couldn't hurt to have the extra braking available, can always restrict it anyway.

Thanks for the input

[Dan]

  I can't see a way to easily get the handbrake to move both shoes if you do that, it will only move one so won't work very well and I imagine that in turn would mean the setup constantly needs adjustment.

[KernowCooper]

Cant see you will get any benefit. the standard rear brakes can exceed the grip due to lack of axle weight as standard and pressure restriction, no ones ever said the rear brakes are lacking due to the weight and pressure restriction

Edited by KernowCooper, 13 October 2013 - 01:37 PM.

[tiger99]

You could end up killing yourself due to a spin caused by locking the rear wheels. You can not safely apply any more braking effort at the back than is achieved by the standard leading and trailing shoe rears.

Also, depending on wheel cylinder diameter, you may not have sufficient volumetric displacement in the master cylinder, and therefore could run out of brakes completely.

There are many important factors that must be considered in a brake system upgrade.

[Rog46]

You could end up killing yourself due to a spin caused by locking the rear wheels. You can not safely apply any more braking effort at the back than is achieved by the standard leading and trailing shoe rears.Also, depending on wheel cylinder diameter, you may not have sufficient volumetric displacement in the master cylinder, and therefore could run out of brakes completely.There are many important factors that must be considered in a brake system upgrade.

Agree entirely if they work you would be continually locking the back wheels (= loss of control + high tyre wear) BUT they might not work at all as you would be moving more slave cylinders with no extra fluid displaced from the master cylinder. At best you would be forever sajusting the brakes to keep rear cylinder movement as low as possible. Don't do it! ! !

[Vipernoir]

Leaving aside the doom of spinning and wheel locking, the more practical answer is that if you do it your handbrake will only really work in a forwards direction.

 

The single leading shoe setup is a single leading shoe regardless of the direction the car is facing - convert to a twin leading shoe (forwards) and you may well struggle to hold a loaded car on a steep hill.

[Cooperman]

There is no point in modifying the rear brakes as they only do a very small amount of the total braking.

[tiger99]

The only reason I would consider modifying the rear brakes would be if I found some nice small disks, with reliable handbrake mechanisms, and small piston diameter to avoid over-braking. The reason would purely be to ease maintenance, as you can check pad wear at a glance. Getting a small disk, or turning a big one down, is the easy bit, getting a caliper with very small pistons might be more difficult.

 

But then, as Vipernoir said, there would be difficulty getting good braking in reverse, when the rear wheels do a significant part of the work, as disc brakes are equally effective (or, in this case we would want them to be ineffective!) in both directions. A direction-sensitive PRV is possible, but adding complexity always adds unreliability, which is not what is wanted in a braking system, as Toyota discovered.

 

I think that what I would ideally like is non-viable. But to throw in another, possibly daft, idea, has anyone ever considered having the handbrake on the front wheels? That is legal (Hillman Imp was an example, I think), and it would give a nice, powerful handbrake, ideal for holding it on a steep gradient. Finding suitable calipers and routing the cables could be challenging!

[Vipernoir]

In an off-road application, a friend converted Metro 4-pot discs to work on the back.
Utilising the split caliper, two of the pistons were attached to the footbrake and the other two to a hydraulic handbrake.  It works a treat.

 

Not sure of the legality of a hydraulic handbrake on the road, but hell, with the loosening up of handbrake regulations on modern cars to allow the frankly ridiculous electronic handbrakes (whatever happened to requiring a physical means of applying an emergency brake ??) there may be scope for development.

[tiger99]

Yes, the hydraulic handbrake is not legal for road use, however a reversed action one where heavy springs hold the brakes on, and hydraulic pressure releases them, is acceptable. There is a requirement somewhere for stored energy to hold them on, to cover for things like temperature change, and in a conventional system that is achieved by the elastic stretch of the cables, sometimes with auxiliary springs built in.

 

But I would still not like that on a car, as a hydraulic failure couild result in the brakes being applied suddenly, which itself may cause an accident. Perfectly ok on trains,which will just stop, possibly acquiring wheel flats is they skid, but a car needs its wheels to be rolling freely if it is cornering hard, and in any case locking the rear wheels is usually inappropriate.

 

I have the same concern about the electronic handbrakes. I think they are a completely despicable idea to pander to lazy idiots who can't be bothered to pull a lever, or who can't coordinate their actions for a hill start, and so should never have passed a driving test. But the big problem is failure modes. Everything can fail, and in possibly a small proportion of cars, will. What does it do? Release the brakes, and let the car roll away on a hill, or apply them mid-corner, and cause a spin? The fact is that there is not a safe failure state for a handbrake, therefore the mechanism needs to be as simple as possible, and capanle of being inspected for deterioration, so that failure on the road is improbable. When you mess with simplicity, you introduce all sorts of additional safety problems, which is one rason that I will never have an electronic handbrake, nor drive a Toyota/

 

Also, with a sluggish electonic handbrake, which is hard on or completely off, how do you do a handbrake turn? We don't want too many boy racers doing tricks on the public highway, but for those with the experience it is an effective manoeuvre of last resort in certain conditions, and has been used to avoid serious accidents. And,how do you stop the car with it, if total hydraulic failure happens (not unknown, despite every modern cat having a dual circuit system), if you can only totally lock the rear wheels?

 

Altogether a thoroughly bad idea, which also costs more.....

 

I think that there will be a serious accident fairly soon which will be attributed to an electronic handbrake, and then it will be found that they do not, in fact, comply with the law. I anticipate a massive recall.....

 

My daily driver has one like this, without the extra buttons surrounding it:

 

http://static.autoex...hoto_282600.jpg

 

That is almost perfection as far as handbrake controls go. I thought I would hate it at first, but declined the electronic option. Everyone who drives the car loves it because it is easy to apply force, it fits the hand naturally, and it is well out of the way when released. Not sure how you could squeeze one into a Mini, as the gap between the seats is somewhat limiting.

[Vipernoir]

Instead of an inverted U handle, how about a thin automatic gearbox T handle ?
That would fit between the seats and apply a magnificent pull on the cables.

[Cooperman]

The standard rear brakes on the Mini make it potentially 'over-braked' on the rear which is why a pressure limiting valve has had to be fitted. So even with standard drums the available braking has been reduced by quite a considerable amount. On some racing Minis the rear brakes used to be blanked off, but the scrutineers didn't like this, so variable rear brake pressure adjuster valves became available. This means that with rally cars where, on gravel, more rear braking is needed to help set the car up sideways for a corner and to improve the ability to get the car more sideways by left-foot-braking whilst applying full power through a corner the pressure can be increased, then reduced for dry tarmac  where the car will not be set up so sideways.

In reality, increasing the rear braking capability will mean simply reducing it again by a restrictor valve to get the actual available braking back to the original, so no actual gain.

 Failure to do this will result in a very unstable car under braking as the rears lock up.

[Ethel]

I'm not sure a hydraulic handbrake is illegal, if it's totally separate, but I'm less sure it'd be a good idea. The more effective you front brakes are, the less effort it'll take for the rear ones to lock the wheels. If you want to get the nth degree of work out of them you need more sophisticated control, an inertia brake limiter valve would be one of the simplest methods.