Twin circuit calipers?

[Alex@POD]

My van (yes, again) will be equipped with twin circuit, two piston calipers at the rear. How do those work internally? Would it be acceptable to use one circuit for the main brake, one for the handbrake? That would make the whole handbrake thing a lot simpler!

[GreenV8S]

Hydraulic handbrake? Technically illegal since you can't get type approval or single vehicle approval without a separate mechanically operated brake. People have been known to bluff their way through with a dummy mechanical linkage, but personally I don't think it's smart to cheat your way through safety regulations.

[Alex@POD]

I knew it had to be a separate system, I didn't know it had to be mechanical. Sorts it then, thanks!

[steve_d]

You have your answer that it has to be mechanical but this did not complete your education on brake calipers.
The caliper, in your case, has 2 pistons with the hydraulic fluid channelled internally or externally to both cylinders so that brake pressure is equally applied. Each piston moves its own pad against the disk to clamp the disk between them. If you only operated one piston you would be bending the disk which would not be a good thing.

Steve

[Alex@POD]

steve_d said:

You have your answer that it has to be mechanical but this did not complete your education on brake calipers.
The caliper, in your case, has 2 pistons with the hydraulic fluid channelled internally or externally to both cylinders so that brake pressure is equally applied. Each piston moves its own pad against the disk to clamp the disk between them. If you only operated one piston you would be bending the disk which would not be a good thing.

Steve

Thanks but that's not how my calipers work. The two pistons are side by side, pushing on the same pad, not opposed like in most cases. My original thought was that for the rear (the calipers come from the front of the vehicle) te force of only one piston would be sufficient, thus freeing the other one for the secondary brake.

[GreenV8S]

Alex@POD said:

Thanks but that's not how my calipers work. The two pistons are side by side, pushing on the same pad, not opposed like in most cases. My original thought was that for the rear (the calipers come from the front of the vehicle) te force of only one piston would be sufficient, thus freeing the other one for the secondary brake.

That sounds unusual, having a two pot floating caliper? In any case, having the main foot brake working on only half of the caliper would be an absolute no-no. The hydraulic handbrakes that you see work in series with the foot brake using the same hydraulic circuit. But as you know, it is a legal requirement for road use that the handbrake is actuated mechanically.

[leorest]

There would be no need to separate the functions of the pistons as it is simple to "T" the handbrake into the hydraulics. BUT the legal requirement to have a mechanical handbrake is your killer! I'm sure I've Googled some small mechanical calipers that would do the job with a bit of suitable bracketry . Just can't remember where I saw them!

[GreenV8S]

leorest said:

There would be no need to separate the functions of the pistons as it is simple to "T" the handbrake into the hydraulics.

Just "T"ing them together won't work because you need to have a closed circuit for the handbrake to work. You need to have an isolator valve or fit them in series. There's a conventional hydraulic handbrake design which plumbs in in series so no difficulty getting it working - the legal issues are the ones that will stop you.

[leorest]

GreenV8S said:

leorest said:

... "T" the handbrake into the hydraulics.

Just "T"ing them together won't work because you need to have a closed circuit for the handbrake to work. You need to have an isolator valve or fit them in series... ...the legal issues are the ones that will stop you.

Fare point. I imagine it's not technically difficult but anyway we seem to agree the legalities are the sticking points!

[steve_d]

Brembo do a small handbrake caliper. I have them on my Ultima.

Steve

[Alex@POD]

Thanks for all the replies, I will look into getting a small mechanical caliper, hopefully one that will fit around my disc!

[steve_d]

Alex@POD said:

Thanks for all the replies, I will look into getting a small mechanical caliper, hopefully one that will fit around my disc!

Ultima discs are 38mm thick. Doubt yours will be thicker.

Steve

[carboy0]

I have seen Audi quattro calipers with two pots on one side - makes for wider pads and more grip/power.

Agree with not using as handbrake caliper. The pistons work together and their actions cannot be split. If you could then you would only be pushing one end of the brake pad which would reduce braking power and put uneven wear on the pad.

Chris