is it possible to use two brake calipers with one lever?

explosifpete

I need to make a brake system for downhill disabled rigs and they don't want to have four levers anymore.
We have tried using a hope brake set with a spliter but the power is poor, they bind on one side and are very spongy.
I have thougght about using a larger flow hose on the first section
any ideas?
also anyone know of hose that would flow twick the oil of a standard hope hose

Barrie_G

I would have though that the main problem would be the size of the piston in the lever, as this will determine how much fluid you can shift down to the calipers, this has probably been the cause of the poor power on your hope system.

DC01

What about a twin master cylinder set up thats actuated by a single lever. Or even sticking with your current setup and using an in line servo assister. This would give a reduction in feel, but would massively increase power. Mercedes use this system or there trucks with a hydraulic clutch and its very effective.

77ric

i can see your issues of splitting the power between 2 callipers equally, as stated above piston size will be the determining factor (although i shall point out that my physics is well rusty) as opposed to hose size. my only viable thought on this would be to run 2 lever/reservoir assemblies piggyback style, but using a single customised lever/blade to drive both reservoir pistons, equal power and separate systems.

send an email to the guys at hope, apparently they are pretty good guys and i'm sure they'd be delighted to offer you any help they can.

redvee

Wasn't there a suspension fork out years ago with twin discs from one lever? Think it was sold by a company in the Cheltenham phone number.

77ric

yeah there was a downhill fork from some company or other that had a rotor on either side.

Anonymous

im sure its gatorbrake or summat:

elPedro666

Plenty of power from the twin discs on my motorbikes...

Perhaps worth looking at the master cylinder to total piston area ratio on a motorbike set up, seeing how it compares to what you have? If you did the same with car systems as well (four calipers) you should get an idea of how the ratio progresses (assuming it does at all) as the number of calipers increases. Servo assists in cars may twist these figures though...

Seems a lot easier to me to start with a twin system that works well and miniaturise it, than try to reinvent it!

Good luck, and let us know how it goes... 8)

biff55

elPedro666 wrote:

Plenty of power from the twin discs on my motorbikes...

Perhaps worth looking at the master cylinder to total piston area ratio on a motorbike set up, seeing how it compares to what you have? If you did the same with car systems as well (four calipers) you should get an idea of how the ratio progresses (assuming it does at all) as the number of calipers increases. Servo assists in cars may twist these figures though...

Seems a lot easier to me to start with a twin system that works well and miniaturise it, than try to reinvent it!

Good luck, and let us know how it goes... 8)

OR maybe offer some practical advice that doesn't require support from nasa's
scientific team.

Mancunianfightingcat

You could get a motorbike brake lever and reservior and the relevant pipe reducers/conectors to mate it to mtb callipers.

or speak to Hope, if there's a growing market, I would think one of the guys there could easily modify a lever to push more fluid through to two callipers.

Northwind

Mancunianfightingcat wrote:

You could get a motorbike brake lever and reservior and the relevant pipe reducers/conectors to mate it to mtb callipers.

That doesn't sound like a good idea, motorbike calipers and m/cs are much larger diameter and so volume.

Are you sure that the issue is the hoses? The volumes of fluid movement in mtb brakes (even in motorbike brakes) aren't that big. If you can find a double banjo bolt you could run twin lines all the way from the lever to the calipers rather than having a split but then, you'll still have the lever's outlet as a potential pinch point if it really is the flow that's the issue.

I'm thinking, a lever off a Saint Quad or similiar combined with smaller calipers would be the simplest way in theory, but in practice getting a good match won't be so easy.

How do you intend to manage front/rear bias? I guess you could do it with different pads and rotors to some extent, maybe even different calipers.

nicklouse

use the 6mm hose not the 5mm hose.

new ends needed.

MarkLG

The diameter of the piston in the master cylinder needs to be matched to the caliper(s) it's connected to. I've had similar problems doing supermoto conversions on motorbikes. If the lever moves too much fluid you'll get a solid lever and little power. If it doesn't move enough fluid the lever will be very soft and pull to the bars before you get any power. Probably best to speak to Hope and see if they can work out the optimal piston diameter for the master cylinder to run a 2 disc set-up. Not sure where you'd find a suitable lever though..
Might be easier to get a full front brake off a large cc moped from a breakers and make an adaptor to mount the disc to your hub.

Hereford Flyer

I'm presuming you are talking about a fourcross machine?
If yes then all the top riders still use 4 levers. Like in the pic:


take a look at
http://www.r-onefourcross.com

Matt 24k

That looks like a couple of Hayes HFX9 master cylinders mounted one on the top of the other. Looks like a simple solution and you could even link the levers with something like this
http://www.demon-tweeks.co.uk/products/ ... BRA167-3DR
The angle of the the clamp would give you a crude adjustment for which lever pulls first. The clamp is actually fpr seperating hydraulic hoses but I am sure it, or something similar, could be adapted.

M1llh0use

i would have thought that using a master cylender from an aprillia rs50 or rs125 with a duel line system to the relavent pair of calipers should shift more than enough fluid but would need special lines made up. maybe worth looking into?

Northwind

M1llh0use wrote:

shift more than enough fluid

That's the problem, you've got to shift the right amount, too much is just as much of a problem because you end up with super-short, super stiff lever action.

I think either Brembo or AP Racing do a 14mm master cylinder, which is about as small as motorbikes go, but that'd still be to push a single 4-pot caliper with piston diametes of about 30mm...

M1llh0use

Northwind wrote:

M1llh0use wrote:

shift more than enough fluid

That's the problem, you've got to shift the right amount, too much is just as much of a problem because you end up with super-short, super stiff lever action.

I think either Brembo or AP Racing do a 14mm master cylinder, which is about as small as motorbikes go, but that'd still be to push a single 4-pot caliper with piston diametes of about 30mm...

what about the performace kit that gets used on the french scooter racing series? AP or brembo stuff?

Northwind

I was wondering about that actually, I've got a Yamaha Aerox front caliper somewhere which is a twin pot. I can't recall how big the piston is though, still pretty big by mtb terms but not as drastically different. But at a guess the surface area's still probably 3-4 times the size of a mtb caliper.

captainfly

Aren't there some 4pot mtb calipers on the market? So there must be higher volume levers availble then uses some smaller 2pot calipers? An email to somewhere like hope asking if they have any compatible parts or at least parts that could work if modded, tell them it's for disabled people/person companies are generaly good about that

The Rookie

why 4 pot pistons are smaller diamter than 2 pot, the same area so shift the same fluid....

Simon

elPedro666

haha, Nasa definately not reguired, just better powers of description!

People have covered it well now anyway - if you double the area of the pistons without changing the area of the master cylinder then you throw out the ratio between them and mess up the feel. Basically you'll need a master cylinder that shifts twice the amount of fluid (not twice the diameter!) to keep the correct ratio.

As for more power; bigger discs just can't be beat!

elPedro666

Should say, to double the area, multiply the diameter by 1.4, so if your master cylinder is 10mm diameter and you've doubled the total area of the pistons, try one that's 14mm.

This post could happily replace all my previous waffle... :oops:

Northwind

Leverage and throw have an input as well though (a 10mm m/c with only 1mm of piston would shift less fluid at max than a 10mm m/c with 10mm of piston). Leverage becomes too complicated for me tbh.

myopic

I seem to remember a thread about this earlier this year where someone had a solution that looked like it would work? I can't find it though

myopic

But on reflection maybe it was the OP with an earlier attempt at this

captainfly

The Beginner wrote:

why 4 pot pistons are smaller diamter than 2 pot, the same area so shift the same fluid....

Simon

So not like on cars and some motor bikes then, that use larger pads and use more fluid and need a master cylinder upgrade fair enough.

captainfly

Am I being thick again? But couldn't you use a twin disc motorcycle set up including the disks or at least kart disks with a bolt hole adaptor??

Lapierre t 400

May I ask which Hope system you are using? If you have a shortage in brake fluid why don't you go to a company that has a CNC machine and ask them if the could make you a kind of extension piece and seal.Instead of bolting you're top cap strait onto you brake lever put the extension piece between the lever and the top cap

26 to Life

It's not that there is a shortage of brake fluid. The problem is that you need to MOVE more fluid. Total oil capacity is (in this case) more or less immaterial.

I remember that 97 Marzocchi bombers had a double disc mount. It will have been with weeny (by todays standards) rotors, and I can't remember who made the hub and braking kit though. Clark seems to stick out but I can't say for sure. I'll have a rummage and see what I can find.

supersonic

You ain't going to get something for nothing. The brake lever will never feel the same as it does on a single set up AND offer the same braking force at each caliper as it would with two levers and two hands pulling with the same force.

Twin discs on forks don't really offer more power, they balance the forces on the fork and improve heat dissipation.

It sounds like you do need to play with bores etc and find a set up that suits ie how much 'power' goes to each brake and lever feel. Increasing leverage results in less caliper piston movement so reduced pad clearance. This may be what you have to do, and something like Shimanos Servo Wave could be of help.