General rear wheel cylinder bore size

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General rear wheel cylinder bore size

mick2009

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Mar 1, 2008
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Hi everyone,
i have a punto 2003 dynamic 1.2 60bhp(with abs) and both my rear wheel cylinders have a slight leak,i want to buy new ones so that someone can do them for me but am a bit confused about bore size as i have seen 2 different sizes listed(20.63 and 22.2),is the bore size critical and can i find out what is on the car without dismantling anything?
what bore size should my punto have as standard?

any advice would be great,

michael
 
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S4p - only list 1 type for 1.2 8v
http://shop4parts.co.uk/?name=store&op=details&ProdId=1169&sku=3594

where as this ebay listing says its the smaller for the petrols

http://www.ebay.co.uk/itm/FIAT-PUNT...arts_Vehicles_CarParts_SM&hash=item45f3fb22c8
20.64


Remember when fitting the new cylinders to fit a nipple cover - to help prevent it rusting like hell

i think i copper slipped my nipples too at one point - dont think this is recommended tho...



Ziggy

theres a possibility you might get blood poisoning
to be honest what you do in the comfort of your own home we really dont need to know anyway:D
 
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the puntos with abs have bigger rear shoes so i would guess they need bigger bore cylinders
frankly if you just use your local motor factor and give them your registration number then they will input this ask if you have abs and throw you the correct part number at about £13
 
Cylinder Area = 3.14 x r^2

r= 22.2/ 2 = 11.1
r^2 = 123.21
Cylinder Area (1)= 3.14 x 123.21=386.88mm^2

r=20.63= 10.32
r^2= 106.5
Cylinder Area (2)= 3.14 x 106.5=334.41mm^2

Cylinder Area (1) / Cylinder Area (2) = 386.88/334.41 = 1.157

Pressure = Force/ Area

Alternatively: -
Force= Pressure x area

From the cylinder area ratio we can conclude, if your original cylinder bore is 20.63mm by putting a 22.22mm bore wheel cylinder you would see 15.7% force increment in actuation force of the rear brakes.

However this increment in actuation force does not directly translate to 15.7% increment in friction force by the shoe and drum despite Friction Force=Mu x Normal force but that depends on the pressure distribution and geometry of the components of rear shoe. You are definately getting more friction force though but how much is not clear without doing the calculation.
 
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