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  #1  
Old 29-05-2010, 09:09 PM
Bozza Bozza is offline
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Default Brake master cylinder ?

I am using a Reliant rear axle with the Golf Mk2 callipers and Nova disc set up.

From what I can gather from other posts my GS850 rear master won't be up to the job.

Can anyone let me know which master works best on this set up please?

Failing that what bore should the new master have?
( ? 3/4 Landrover item ? )

Thanks

Bozza
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  #2  
Old 30-05-2010, 07:34 PM
Blackjack Blackjack is offline
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I'd use a 5/8" one.

Sort of ball park for most stuff is a 5/8" master cylinder with around a 6:1 pedal ratio.

The pedal ratio thing gets missed by a lot of people.
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Old 30-05-2010, 09:31 PM
Bozza Bozza is offline
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Default Master cylinder

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Originally Posted by Blackjack View Post
I'd use a 5/8" one.

Sort of ball park for most stuff is a 5/8" master cylinder with around a 6:1 pedal ratio.

The pedal ratio thing gets missed by a lot of people.
Hi Blackjack,

Could you explain the pedal ratio thingy a bit please?

Isn't 3/4 an eighth bigger bore than 5/8?
Bigger bore more fluid pumped or have I got it all wrong.

Thanks for your help.

Bozza

Last edited by Bozza; 31-05-2010 at 08:44 PM.
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Old 30-05-2010, 11:46 PM
kajay kajay is offline
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If the length of lever connected to the master cylinder linkage is 1" above the pivot point you will need 6" below the pivot point connected to the brake pedal to give you more leverage.

I think the smaller master cylinder is the better option as its a smaller surface area and you then get more pressure, at least I think thats correct
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  #5  
Old 31-05-2010, 04:46 PM
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v8_trike v8_trike is offline
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I just fitted one of these:

http://cgi.ebay.co.uk/Land-Rover-Ser...item230765811e

plenty of stopping power using the same Nova / VW set up as yourself
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Old 31-05-2010, 07:58 PM
Puppydawg Puppydawg is offline
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I used Landrover master cylinders for both clutch and brakes on my Mini trike and there spot on !
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Old 31-05-2010, 08:42 PM
Bozza Bozza is offline
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Default Trike master cylinder.

Thanks again guys.

But.......is it 5/8 or 3/4 bore?????????????

Bozza
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Old 31-05-2010, 09:02 PM
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harry harry is offline
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Quote:
Originally Posted by Bozza View Post
Hi Blackjack,

Could you explain the pedal ratio thingy a bit please?

Isn't 3/4 an eighth bigger bore than 5/8?
Bigger bore more fluid pumped or have I got it all wrong.

Thanks for your help.

Bozza
Many people get confused with master cylinder bore sizes.

When you press the pedal it's like a seesaw or a lever. The end of the lever you are pressing on needs to be longer than the other end pressing on the master cylinder. A ratio of about 6 to 1 is a good place to start.

For a given effort on the pedal a smaller piston will give you a greater fluid pressure 'cos of the smaller area of the piston. Thats why we measure fluid pressure in pounds per square inch etc.

However if the master cylinder is too small it wont shift enough fluid and you may run out of travel before the brakes are fully on. This can be
inconvenient.

If you use a bigger bore master cylinder you will need to have more leverage on the pedal to compensate. I got it wrong first time on my trike and had to move the pedal pivot to get more leverage If I build another I would try to make the ratio adjustable.
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Old 01-06-2010, 11:57 AM
Blackjack Blackjack is offline
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Yes.

And...

Bike 5/8" master cylinders will TEND to be shorter stroke than car ones, thus displacing less fluid, since you now have to work 2 brakes with it.

Build a 3;1 pedal, work a 2;1 idler with it, work the m/cylinder with that.

Turns out the ratios off, you only need to fiddle with the idler.

Make the idler 1.5:1 you have an over all ratio of 4.5:1

Make the idler 2.5:1 you have a ratio of 7.5:1.

Easy peasy.

Don't fart about buying "Land Rover" or whatever ones, just go somewhere like this and buy on the spec...

http://www.nfauto.co.uk/master_cylinders.htm

They do rose joints and clevises for the linkage too...
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  #10  
Old 01-06-2010, 05:32 PM
Bozza Bozza is offline
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Default Master cylinders

Quote:
Originally Posted by Blackjack View Post
Yes.

And...

Bike 5/8" master cylinders will TEND to be shorter stroke than car ones, thus displacing less fluid, since you now have to work 2 brakes with it.

Build a 3;1 pedal, work a 2;1 idler with it, work the m/cylinder with that.

Turns out the ratios off, you only need to fiddle with the idler.

Make the idler 1.5:1 you have an over all ratio of 4.5:1

Make the idler 2.5:1 you have a ratio of 7.5:1.

Easy peasy.

Don't fart about buying "Land Rover" or whatever ones, just go somewhere like this and buy on the spec...

http://www.nfauto.co.uk/master_cylinders.htm

They do rose joints and clevises for the linkage too...
I have no idea what most of that means!!!!!!!!!
I will show it to a man that might know about these things at the weekend.

Thanks for your time replying.

Bozza
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  #11  
Old 02-06-2010, 11:16 AM
Blackjack Blackjack is offline
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Quote:
Originally Posted by Bozza View Post
Thanks again guys.

But.......is it 5/8 or 3/4 bore?????????????

Bozza
Think of it like this...

You put some pressure onto the lever and that flows along the rod into the master cylinder. The pressure is then divided up amongst the fluid that comes out of the master clyinder.

Bigger bore, more fluid, less pressure.

Smaller bore, less fluid, more pressure.

"Pedal ratio" just means the leverage you have to apply pressure to the master cylinder. A 6:1 ratio is multiplying the pressure you apply by 6 times.

Normal sort of bike forward controls will have a ratio of around 4:1 and multiply the pressure by 4 times. This means the pedal will be very "hard", not move very far (if you've led the brakes properly), and the brakes will be shit.

So, if you make the rod operate one end of a lever that's 3" long and flopping on a pivot at the other end, and has a second rod coming off of it thats 2" from the pivot that connects to the master cylinder, that has a ratio of 3:2.

Because we did maths at school and knew it was going to come in handy for things like building trikes, and so paid close attention, we know that a ratio of 3:2 divides out to 1.5:1.

Since the pedal multiplied the effort by 4, and the extra lever multiplies that effort by 1.5, you end up with (4 x 1.5) times the original effort, or 6 times.

By altering the ratio of the extra lever you can fine tune the pedal ratio. This is cheaper than buying a different master cylinder.

You can use the "extra" lever (or idler) to convert a pulling force to a pushing force too, which is handy if you're using forwards because pushing on long rods is a shit idea.

As a rule of thumb, a 5/8" master cylinder with a 6:1 pedal ratio is usually in the ball park, but having 6" brakes and 19" car wheels means that the tyre has a lot of leverage on the brake, and means that the braking force at the wheel is reduced. If that's the case, what you actually need is bigger brakes, because cranking the pressure up will just make for a "grabby" brake that's in danger of blowing the seals on the wheel end of things.

As an observation, you seldom see cars equipped with discs or drums with a diameter of less than than 1/3 (or so) of the rolling diameter of the wheel and tyre. So, I'm inclined to think that using that as a guide to the minimum ratio between wheel size and brake size would probably work out OK....

Last edited by Blackjack; 02-06-2010 at 11:26 AM. Reason: Forgot some shit...
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  #12  
Old 02-06-2010, 09:26 PM
odie odie is offline
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I had the disc brake conversion on my last trike, ran with a bike rear mater cylinder with a 14mm internal bore, locked the wheels piece of piss.
Think it came off a ZZR or ZX10, some big kwack.
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