hydraulic handbrake for the rear wheels

[Teuski]

I just bought a BX 16V for a hobby racer project. Well, it's not an actual 16V but a 16 GTi (i guess it's a finnish special, 19GTi with a XU5JA engine) fitted with a 16 valver and the skirts.

I'm building it for sprint races on a mixed surface rallycross track and ice racing. It's going to be a low budget project, at first i'll just strip all excess weight, fit in a a rollcage and a racing seat and lock the diff up. It has a 16 GTi gearbox which i guess is the same as in a 205 1.6 GTi. The gear ratio is very short, which is good and i'm going to keep the box as it is.

The engine will stay stock too, as the purpose is to build a car that doesn't have to be repaired all the time. One goal is to show all those paople who think that the hydropneumatic suspension is crap that actually that's not what it is

Anyway, the thing i was going to ask was if anyone has ever tried to build a hydraulic handbrake for the rear wheels?

I was think if some kind of a 3-way hydraulic valve that could be used to bypass the brake valve and feed the pressure straight to rear brake circuit. It should also close the connection between the actual brake valve and the rear brake circuit to prevent the operational return of pressure as the pedal is not pressed.

The coolest way to operate the handbrake would be a button on the steering wheel to control an electric valve.

There isn't much need for a rear handbrake, but i'm just interested if it could be done

[Vanny]

If you have a search around there is an American couple who compete in UK classic rallies in a bright pink Citroen DS, and it has a hydraulic rear 'hand brake'.

My understanding is that there is a three way union in the main master cylinder to rear brake line. A pressure source is then tapped possibly direct from the front of the car (possibly this could be done from a spare port on the FDV on a BX?) through a height corrector and into the three way. The height corrector is connected to an additional hand brake lever.

As i'm usually marshaling the events, i've never had chance to flag the car down and ask the question of 'how', but when you see the might of a DS hand brake turning around a rather large bail of hay on a very small piece of tarmac, you can understand why it is needed.

I believe the CX Turbo has an electronic height corrector, though i have no idea if it would be fast enough? I don't know if it is an electrovalve or some sort of servo driven unit.

The other option is to use a standard hydraulic hand brake control designed for DOT4 and either replace the seals or see how things go?

Alternatively you could use a control from a plant machine like a fork lift truck, they usually have a small compact size with a short throw so it would be more akin to on/off than a hand brake (which is what i think your after). Having competed in the BX on a very tight autosolo course, i did find it very infuriating to watch other competitors gaining a much quicker time through the corners due to having a hand brake!

Not that I've ever given it any thought!

[Teuski]

Good ideas!

That solution with a height corrector sounds good.

I was thinking of a 3-way valve with 2 inputs and one output. One input to brake valve, other directly to the HP supply (a spare point on a FDV would be super) and the output to the rear brake circuit. Then the valve would select between the two inputs, either normal brakes or direct HP feed to the rear with no return through the brake valve.

I'm also interested in adjusting the brake bias. I've heard there's an adjusting screw for the rear brake circuit in some brake valves? Is it true and where can I find such valve?

[Adrian E]

May also be worth considering some of the newer cars with electric parking brakes?

Maybe something like the mechanism from a Megane Scenic, or Jaguar, with an additional pair of calipers?

Granted the hydraulic solution using the OE calipers would be a much neater solution, but if that proves problematic the electric option would be worth a look

[Teuski]

Granted the hydraulic solution using the OE calipers would be a much neater solution, but if that proves problematic the electric option would be worth a look

The hydraulic solution would be THE solution, others would just be a compromise

Inspired by Vanny's post i studied the height corrector and found out it might do the trick.

Here's an illustration from a guide:

I'd run a HP feed to the feed port of the HC, possibly straight from the FDV if there's a spare port. The return would connect to the actual brake valve instead of the rear brake circuit, and the circuit itself would be connected to the strut port of the HC.

The handbrake lever would then control the height corrector, which would retain normal brake operation in lowering position but when switched to rising position, it would feed the rear brakes with pressure and prevent the return through brake valve.

Doesn't it sound easy?

[Vanny]

My understanding is that it IS that easy!

It would be interesting to see how the BX EVO 4TC rear handbrake worked, i believe the Xantia rally car used something similar (though it had front struts at the back, and the radiator so was less than standard.


I'm sure there is a schematic on the web of the FDV and its ports, it might be on bob smiths site.

[Simran]

is there any chance that 205 rear calipers would fit? They look just like our front brakes and have a cable operated handbrake. Swap the seals over for something suitable with lhm and hook up the cable to the existing lever.

Ive got to admit the idea of a little button on the steering wheel or dash for an electric control for the hydraulic system handbrake would be uber cool though, i definitely want one

[Teuski]

is there any chance that 205 rear calipers would fit? They look just like our front brakes and have a cable operated handbrake. Swap the seals over for something suitable with lhm and hook up the cable to the existing lever.

Ive got to admit the idea of a little button on the steering wheel or dash for an electric control for the hydraulic system handbrake would be uber cool though, i definitely want one

Of course it would be possible to fit calipers with a mechanical handbrake, but that's not what i want. I want to use the existing high pressure system.

The electric button could be used with the height corrector solution too, just add a small servo

[surjit25]

Maybe you could try to fit the BX frt calipers to the rear
and fabricate 2 cables.
Trying to tap into the hyd. system might have its drawbacks,
when you switch off,and pressure decreases , the h/brake will fail.
unless you fit a anti-sink valve to prevent the pressure from returning.
Or also fit calipers from the s/wagon which are bigger and bite more, the ori. rear pads are pretty puny.

[Vanny]

Beyond the fact that you should ALWAYS ALWAYS leave a hydraulic Citroen in gear, and thus don't need a hand brake when the engine is off, the purpose of the rear hand brake is NOT for parking, or holding the car, but to lock the rear wheels to break traction and induce a slide. If you have ever done any motorsport on a tight twisty track you'll realise that you can get round a corner much fater in FWD if you can slide the back out.

I guess the name is miss leading, it's not a hand brake thats needed as such but a locking brake, you certainly don't want a hand brake that sticks on for this sort of work. I know a lot of auto solo drivers who have many different modifications to there normal hand brake so that it does not lock on.

And because of this purpose, hydraulic is the way to go.

Personally i would add the HC, connect to it by bowden cable and have an actuator on the dash, no point in moving your hand all the way to the floor of the car if you don't need to.

Thinking about this earlier, i wonder if C5's have an electronic height corrector and what sort of signal it requires.

[surjit25]

LIke that all you need are the bigger calipers fitted to the rear
a 2nd brake valve (doseur) fitted to supply pressure directly.
It can be done.

[Vanny]

where would you get bigger rear calipers from? BX rears are all the same, CX rears are the same as the BX, Xantia rears are all the same, my understanding is that C5 rears wont fit at all, and i have no idea about the XM. It could be interesting to increase the rear size, but i didnt think there where any options?

[surjit25]

I hv never seen BX wagon rear brakes which should be bigger
but CX and Xantia both have bigger disc and calipers.
The arms for xantia and BX are interchangeble but anti
roll bar are diff. bigger and thicker for xantia wagon

If you wanna just change the calipers then some mods are needed as the distance between the caliper screwhole mounts are further apart

[Teuski]

LIke that all you need are the bigger calipers fitted to the rear
a 2nd brake valve (doseur) fitted to supply pressure directly.
It can be done.

Wouldn't that solution let the pressure escape through the actual brake valve?

Let's forget these cable-operated brakes, they are out of the question
Another pair of calipers sounds like too much work, as i am pretty sure it could be done in a simpler way using the existing rear brakes.

On another forum I was told that the heigh corrector has some kind of damping and it would be too slow.

Maybe i should ask a local specialist shop for all kinds of hydraulics if they had a good valve for the purpose.

Most hydraulic handbrakes in racing I've seen have a big vertical lever near the steering wheel which is either pulled or pushed to engage the rear brakes.
Why not put a fourth pedal, now that's left foot braking!

[Vanny]

You can remove the damping from the height corrector very easily i believe. There is a stack of discs/plates in the middle that provide the damping, simply remove them. The corrector is after all only a switch. But i would serious look into hydrualic controls for a fork lift or mini digger, they are very easy to get hold of.

Surjit, all BX models and variants have the same rear calipers and discs, including the 4x4 and estate. The Xantia's i believe all have the same size, but certainly the diesel estates and Mk1 cars have identical rear caliprs to the BX. And the caliper is a carry over from the CX so most if not all of them are the same.

I have never found a bigger rear caliper for the BX from any 'modern' citroen.