Is this easily doable via some sort of splitter?
Basically I am experimenting with an additional high bar position ( ala sheldon) on my MTB tourer …due to back issues) .
Having an extra position to ease the back on flatter or downhill sections is great but I am very aware of the lack of brakes and find it likely I shall forget one day and need to stop in a hurry but not have time to change position.
I had thought of running an additional v.brake at the back perhaps, as my frame has bosses, but would also have to have a wheel rebuilt with a suitable rim which was not disc specific.
I then though I wonder if I could simply add another lever/master cylinder and T it in to an existing brake line , hence the thread.
Any ideas, opinions ( preferably constructive) would be appreciated.
Thanks in advance.

It’s not doable with standard levers, as pulling on one lever will just push fluid into the reservoir of the other.

Shimano’s GRX has optional cross-top levers which are designed to be put inline between your main levers and the calipers.

https://bike.shimano.com/en-EU/product/component/grx-11-speed/BL-RX812-R.html
https://road.cc/content/tech-news/206054-hope-unveils-new-inline-hydraulic-crosstop-brake-levers-paul-oldham-winning

My first thought was that you might be able to bodge a dual cable pull on some TRP HY/RD units?

The GRX/Hope units units look interesting..wondered if they will work ok inline with MTB master units as they seem to be designed for road systems. Whether that makes any difference ?

you will be able to do it – you need a splitter and non return valves. Try Ben at Kinetics in Glasgow?

Ir you could do it with a cable to hydraulic converter adn two cable levers
I’ll have a google later.

you need a splitter and non return valves

Isn’t that going to lock your brakes on?

wondered if they will work ok inline with MTB master units

I can’t see why the GRX unit wouldn’t work with MTB levers. The use the same hoses and push the same amount of fluid as the road stuff.

Wonder if we will see GRX dual braking on TT bikes soon, so you can have a set of levers on the aero bar for an emergency stop when using the bar.

you need a splitter and non return valves

Isn’t that going to lock your brakes on?

Yes, it will. It’ll work for the first pull – the fluid from lever 1 won’t be able to pass into the reservoir of lever 2, it’ll all go to displace the pistons. However, when you release lever 1 the fluid won’t be able to return to the reservoir of lever 1, where it came from. It can’t be a simple passive hydraulic system inho, unless you had a mechanical part in the place of the splitter, with 3 separate hydraulic systems linked mechanically.

Sounds like the Hope/GRX in-line system is the simplest solution

a set of levers on the aero bar for an emergency stop when using the bar.

That’s not going to end well.

Correct on the one way valves. It would have to be some sort of diverter valve

Can’t you just use a cable disc?

I’m sure you used to get secondary levers for v/canti brakes that should be fine with discs. They were generally rubbish because of the change in leverage from flat to drop levers but it’s certainly doable.

If you can get some old hope C2 master cylinders (or others from closed systems), I recon that should work with a t piece in the hose as there is no separate reservoir.

Closed system won’t work as the master cylinder cap will be exposed to high pressure under braking which is not how it was designed.

What about fitting 2 calipers? Could a clamp on mount be attached to the seat-stay to provide a second caliper position?

Some good ideas…many thanks…will look in to GRX and cable ideas.

If you’re going the hybrid cable/hydraulic route then Giant do “Conduct” which is a stem mounted, cable actuated hydraulic brake.

Closed system won’t work as the master cylinder cap will be exposed to high pressure under braking which is not how it was designed.

I thought it was? Thats the ‘closed bit as opposed to modern open brakes having the reservoir open to the atmosphere so the fluid has somewhere to go when it warms up.

Yep closed system so same pressure without the system.

I think the point is that the cap that retains the lever piston is designed to hold the force of the return spring, not the force under braking. If you used a closed lever as a secondary lever then when you pulled the other lever, the secondary piston would be pushed back against the retaining cap with the same force that you’re applying to the primary, which will be rather more than it was designed for.

Would be silly to attempt with hydraulics. Better to have cable actuated levers operating a cable to hydraulic unit, like the Hope V Twin unit. Several bikes have two cable brake levers operating single cable brake, so just put the V Twin unit after the brake levers and you operate hydraulic callipers.

I think hydraulics are actually better for this, it’s just that you can’t do it by combining normal levers. You need a lever designed for the purpose, which fortunately is now available.

The master cylinder has a small opening at the top which is in front of the seal when the lever is fully retracted. As soon as you press the lever, the seal closes off this orifice and forces all the fluid down the hose. Once the lever is retraced again the fluid is free to circulate from the master cylinder. You can adjust the amount of fluid downstream of the opening with the dial on the reservoir to account for pad wear and heat, but the seal on the reservoir is never exposed to the forced generated by the master cylinder.

Thus I concur with @onzadog – while it may work, it certainly isn’t intended to work that way.

turboferret – you are describing an open system. Closed systems do not work like that.

@hols2 I was under the impression that the difference between a closed and open system was that the reservoir in an open system has a diaphragm with the upper surface open to the atmosphere to allow natural changes in fluid volume while a closed one controls how much is in the system by altering the reservoir volume. That’s certainly what I gleaned from disassembling old Hope brakes and my time working with brakes at Middleburn. Is there something I’m missing?