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Bob uk
Unregistered guest
Posted From: 94.197.122.79
Posted on Thursday, 24 July, 2014 - 06:23 am:   Edit PostDelete PostView Post/Check IP

SY with master cylinder.

No1 system 31% front 16% rear.
No2 system 31% front only
Master 22%
Handbrake over 16%
Total front 62%
Total rear 38%

Ram pressure 1150psi 3 inch stroke

(Message approved by david_gore)
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Bob Reynolds
Prolific User
Username: bobreynolds

Post Number: 127
Registered: 8-2012
Posted on Thursday, 24 July, 2014 - 03:18 pm:   Edit PostDelete PostView Post/Check IP

Interesting to see that the master cylinder provides nearly a quarter of the braking force.

I wonder on cars without the master cylinder, is the total braking force reduced?
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1232
Registered: 6-2006
Posted on Thursday, 24 July, 2014 - 04:55 pm:   Edit PostDelete PostView Post/Check IP

Hi Bob,

percent of what? spurious figures without context are confusing and pretty meaningless. Did I miss something?

When is this supposed to be true for?

You will not be using the parking brake when travelling.

If the car is braking whilst travelling downhill, a larger proportion goes to the front.

The harder you brake the higher the percentage of total force goes to the front.
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1233
Registered: 6-2006
Posted on Thursday, 24 July, 2014 - 04:59 pm:   Edit PostDelete PostView Post/Check IP

You never use 100 percent of the accumulator pressure when braking so overall braking force will not be affected by the master cylinder, just by pad to disc friction and used to road grip.
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Bob uk
Unregistered guest
Posted From: 94.197.122.73
Posted on Friday, 25 July, 2014 - 06:09 am:   Edit PostDelete PostView Post/Check IP

Ignore the handbrake over 16% is for mot test reasons

The percentages total 100%

Ignore the weight transference.

When the brakes are applied the settings that are designed into system that cannot be changed ( size of pistons length of levers in the rat trap) dictate the front to back brake balance.

So for any given amount of pedal application the system will grip the discs in that ratio.

If the front brakes pistons are applying say 620lbf to the discs then the rear will apply 380lbf to the tear discs.

Wieght transference does not effect this.

Under heavy braking the de acceleration valve will limit the rear which does not give more to front.

But normal slowing down 62% front 38% rear

The sy2 has no2 connected to where the master was connected on the sy1

No 1 47% (31f/16rear)
No2. 53% (31F/22rear)
No master.

Now when we consider weight transference because the rear is getting lighter because under heavy braking the de acceleration valve prevents the rear wheels locking. Bad grammar.

Master cylinder
RR use the term low pressure. The pressure is not that low because the pressure of the master circuit is the same as the power circuit at THE CALIPERS. And because of the de acceleration valve on the rear caliper power circuit the master pressure can exceed the power circuit.

(Message approved by david_gore)
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Bob uk
Unregistered guest
Posted From: 94.197.122.82
Posted on Friday, 25 July, 2014 - 08:02 am:   Edit PostDelete PostView Post/Check IP

The point of the above is that the master circuit which is the same as "normal" brakes works at about the same pressure as the power circuit.

In emergency stop events the power will go to 2500psi. And so will the master.


There fore normal brakes on other makes are also at this pressure.

There is a notion in RR circles that the system works at a higher pressure than others.

Actually it doesn't.

If the master circuit was of lower pressure then the rear pads would be wedge shape.

A normal system could be made to stop a shadow but it will feel like my Cherokee which is **ite

(Message approved by david_gore)
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1234
Registered: 6-2006
Posted on Friday, 25 July, 2014 - 08:10 pm:   Edit PostDelete PostView Post/Check IP

wrong,

the G valve reduces pressure tm only two pistons with heavy braking.

Piston sizes are different on master and non master cylinder cars.

pressing the brakes lightly just operates master cylinder pistons.

braking hard on later cars reduces pressure to one end of pads.

no wedge shaped pads because you don't just always brake heavily or just brake lightly.


There is no one set or figures that spans across the whole driving range.


The high pressure system does most of the work with no driver effort. Thankfully.
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Bob uk
Unregistered guest
Posted From: 94.197.122.93
Posted on Saturday, 26 July, 2014 - 06:07 am:   Edit PostDelete PostView Post/Check IP

Paul
You are correct.
The g valve under heavy braking will limit the pressure to half the caliper and in extreme stoppies no pressure at all. The master is then the only rear brake.

On normal cars with a weight sensitive valve under extreme braking the rear would often have no brakes due to weight transference lifting the rear.And shutting the valve causing the car to be unstable and liable to spin out.

The refinement of always having a rear brakes regardless makes the shadow very good under extreme braking events. It is as good as the very best modern cars.

If the anchors slammed on then the front will get the full 2500psi. The valve will snap shut ( when bleeding you have to be gentle with the gvalve because it will shut and block dot flow)

The master will develop about 2500 psi as well

However a mere 1000psi will grip the front discs with 8 x 2 inch pistons 24000lbf

The front wheels will lock so the actual peak pressures are academic.

The master has no relief valve so press the pedal hard enough and the pressure will soar.

On a brake dyno the rear wheels will easily lock with engine running. With no pressure and master only a strong person can lock the wheels.
Both feet.

The balance ratios quoted are from 1965 UK type approval data.

About 1968 the system was rejigged.
The master was connected to the smaller pistons and power to the large ones and g valve .

Chassis no 1877 on.

This left the front back ratio at the same 62f and 38 rear.

The rear caliper power pistons 22% and master 16 %

I can't lock the rear on the master only but if I pull the handbrake hard I can.

At speed the hand brake will heat fad

(Message approved by david_gore)

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