Brake Line Pressures

[tref]

Gentlefolk,

Does anyone know off the top of their head what pressure can be achieved in eth brake lines of a 944 S2 or Turbo? I am refurbing a set of callipers to go on Bomber, and I wanted to pressure test them (I have some good facilities available to me!) prior to fitting.

I know I could work it out by seeing how hard I can squeeze eth brake pedal, and calculate from master cylinder diameter, servo diameter, blah, blah, but if some-one knows it could save me an awful lot of head scratching!

Many thanks,

Tref.

 

[924nutter]

circa 2,500 3,000 psi, and I have read in some old practical motoring mags engineers articles suggesting that cars have been presented for mot with clear plastic pipe substituted for the real macoy.
Assuming about a 9:1 fulcrum ratio on the brake pedal and 100lb of push from you left welly that gives about 710 lb of force on the M/C for a one inch dia (25mm piston) and say a 2 inch caliper piston that give pi times 710 which is > 2130 psi. Completely guesstimated but educated guess. Add in servo assistance and the figures are right in the ball park

 

[tref]

Brilliant, gives me some sort of figures to play with... except the pressure at the caliper will be the same as at the master cylinder, just the force will be greater as it is acting over a larger area - correct me if I am wrong, please!

 

[zcacogp]

ORIGINAL: tref
... the pressure at the caliper will be the same as at the master cylinder, just the force will be greater as it is acting over a larger area - correct me if I am wrong, please!

Correct. PSI = Pounds per Square Inch.

Assuming frictionless fluid and zero energy loss, multiply the PSI by the area (in square inches) of the back of a caliper piston and you will get the force exerted by that piston. Bigger piston = bigger area = bigger force (which is why calipers with bigger pistons squeeze harder than those with small pistons.)

John's calculation works fine although the extra force comes from the servo assistance, rather than from the calculation of caliper piston size.


Oli.