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Secondary/auxiliary brake levers - hydraulic?

Old 07-13-23, 06:41 AM
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If you had two brake levers attached to one brake with that t piece, when you squeezed one lever it would just force oil into the reservoir of the other lever. I can see two brakes on one lever but not how it would work the other way around.

I then thought, "Hey, we're dealing with fluid here, not cables, so a T-piece should be a doddle", and so normal flat bar brake levers should work fine as secondaries.


I dont understand this part. I have an academic interest in this project though I think it is still (some of) a solution looking for a problem. If you try anything out, post here. Cool!
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Old 07-15-23, 06:20 AM
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Originally Posted by tombc
If you had two brake levers attached to one brake with that t piece, when you squeezed one lever it would just force oil into the reservoir of the other lever.
Hmmm....

It would seem a little overcomplicated for a brake lever to be able to pressurise the fluid when gripped, but to permit ingress of fluid when in the relaxed state (not gripped).

If you ask me, a brake lever in the relaxed state will NOT permit ingress of fluid, should the fluid pressure be increased , e.g. by another brake lever.

Therefore, whichever lever is gripped, it will have the same effect on the disk brake calliper as if only one lever was attached.

Conversely, if a crazy cyclist attempted to operate both levers simultaneously, they would be additive, pressure-wise.

So, the only remaining issue is to find a compatible hydraulic brake groupset, e.g.
  1. 22mm dia drop handle bars (yes, they exist)
  2. TRP Hylex drop brakes (22->24mm shims?) & calipers
  3. Brake hoses?
  4. T piece (Tektro, Magura, other?)
  5. 22mm dia bar clamp hydraulic brake levers (secondary)

Last edited by Xavier65; 07-15-23 at 06:24 AM.
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Old 07-15-23, 06:27 AM
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Disc brake levers have a bladder in the reservoir to allow the pads to self adjust. the pads would close and then if you kept squeezing it would blow the reservoir in the other lever.
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Old 07-15-23, 06:34 AM
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Originally Posted by tombc
Disc brake levers have a bladder in the reservoir to allow the pads to self adjust. the pads would close and then if you kept squeezing it would blow the reservoir in the other lever.
Sounds complicated. :-}

Maybe not all brake levers have this feature?

Anyway, that would then be solved by a T piece with a pair of one way valves, or a single switch-over valve (if such a thing could exist).
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Old 07-15-23, 06:47 AM
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Ok, so thanks to the pesky sniffer hole, that does indeed mean that the lever will accept fluid ingress when in the relaxed state, this means that either a T piece with valves is required, or, that a special secondary lever is required, i.e. that performs an equivalent function,

So, it's back to the Shimano GRX secondary levers.

However, to get them further from bar centre one may then require 22->32mm shims.

So thanks tombc for your expertise.
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