ecosse
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| posted on 19/1/06 at 07:17 PM |
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Brake question
Can anyone tell me what size master cylinder (bore size?) I should be using for a single master cylinder based system?
Or does it not matter greatly?
Is anyone using a balance bar twin master system out there, is it much of an advantage, or is an adjustable valve with a single master as good an
option?
Any opinion/advice appreciated
Cheers
Alex
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britishtrident
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| posted on 19/1/06 at 07:42 PM |
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All covered many times over
For ordinary road a dual balance bar set up has no advantage but it is very popular where the car is intended mainly for track use but isn't a
major advantage over a rear presure limmiting valve. A pressure limmiting valve may or may not be required it depends mainly on what rear disc or
drums setup you use.
Bore of master cylinder depends on pedal leverage ratio but most master cylinders from cars with servos are on the big side for use without a servo,
for a single master cylindr system 0.75" (19mm) is about the best size you can hope to find in a tandem dual circuit cylinder although Westfield
used a 0.7" that was only fitted to some Triumph models and Fx4 Taxis -- second hand Westfield cylinders sometime turns up on ebay as they are
not require when the brakes are upgraded.
Dual master cylinder balance bar pedal boxes generally use 0.625" or 0.7" bore cylinders --- sometimes one of each if the brake balance
is far off centre with two equal sized cylinders.
[Edited on 19/1/06 by britishtrident]
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JB
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| posted on 19/1/06 at 07:46 PM |
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Brakes
The master cylinder bore size depends on many factors, but mainly the bore size of the brake calipers / cylinders.
The worst thing that can happen is to have one that is too small and not be able to move enough fluid. If it is too big then pedal pressures will be
high.
So always go on the large size.
A twin master cylinder set up will allow you to have different setups front and back. Fred Puhns Brake HandBook has formula to calculate what you
need. (I used them on my car and the setup only needed minor tweaking with the balance bar)
Basically it looks at pedal effort (levarage) master cylinder bore size, caliper bore size, disc diameter, tyre diameter, tyre friction and centre of
gravity.
You soon realise that you require a different front rear bias in the dry to the wet due to different weight transfers involved.
For example on ice you can have a 50 50 front rear split, but on sticky slicks this may be 80 20.
This is where the fancy brake proportioning valves come in. They basically limit more under high line pressures (dry conditions therefore large weight
transfers) and less under low grip conditions.
So back to the main point, twin master cylinders are great, a balance bar allows easy fine tuning, and a brake pressure valve allows optimum braking
in all grip conditions.
I single MC is simple and easier to fit but for the better performance fit twins.
John
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ecosse
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| posted on 19/1/06 at 08:35 PM |
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Brilliant, just what I needed to know.
Looks like single master with pressure valve best compromise.
Cheers
Alex
PS
I'll check previous posts first next time though 
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britishtrident
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| posted on 20/1/06 at 11:08 AM |
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New Polo/Golf non-servo master cylinders are very cheap -- but they come without the resevoir so it intails a trip to the scrappie.
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ecosse
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| posted on 20/1/06 at 11:45 AM |
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Good to know, thanks, is this cheap from the dealers or from somewhere else?
Cheers
Alex
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