Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Rear brake linings replacement - 2011 +4

That's a bit of useful info +8Rich, your original equipment cylinders are 23.8mm diam, i am therefore satisfied that the BCW5099 at 23.8mm (rechecked the website the BCW5099 is in fact 23.8mm diam and not 22mm as i originally stated in first post) is the correct one for the job, thanks for that.

Small bore = longer travel = less pressure.

But doesn't small bore for the same pedal movement mean more travel?

Is there an hydraulics expert in the house?

The braking system of a car is a series of levers. Some are mechanical (pedals and brake shoes for instance), others are hydraulic.

Small bore master cylinder operating large bore slave cylinder = more pedal travel = more leverage. Think of the the diameter ratio between master and slave like a lever ratio. A 10mm master cylinder driving a 20mm slave cylinder gives a 2:1 leverage - same effect as putting the fulcrum 1/3 the way along a lever.

Hi lowlier, Reading your article on the rear brake replacement did you managed to find the spring wave washer and retaining spring washer/retaining clip for connecting hand brake lever to the brake shoe, if so where did you get them from. TIA .

Is this the set you are after ?

As you try to move from a larger diameter to a smaller the pressure increase. The fluid has to travel further in a smaller bore for the same displacement of volume in a bigger bore pipe. Basically the system follows the conservation of energy concept.
Try blowing down a 1/2 inch pipe and then a straw, you will feel the increase in pressure as the diameter narrows. Basically the system follows the conservation of energy concept, as Paul say's it is effectively a lever.

I looked at my old Uni book on the subject "Fundamentals of Momentum, Heat & Mass Transfer" by Welty, Wickes & Wilson. I realise firstly how much I have forgotten but it is a gripping read on the subject for someone but probably not for me.

I find the easy way to remember this is larger bore master cylinder gives harder (shorter travel) pedal but less mechanical advantage so weaker braking for given amount of right foot.

Larger bore slave cylinder gives softer (longer travel) pedal, more mechanical advantage, better braking.

Adding pressures into the equation adds confusion for me.

We must not get confused with pressure versus force. Effectiveness of the brakes depends on the force being applied to the brake shoes. You can put what size of slave cylinder you like and it won’t affect the pressure. The pressure is created by the piston in the master cylinder, acting on the volume of fluid in the pipes etc. What does change with different sized brake cylinders, is the FORCE acting on the brake cylinder piston.
Force=Pressure x Area, so for a constant pressure applied via the brake pedal, increasing the piston diameter of the brake cylinder will increase the force acting on the brake shoes.

Doug, your use of English is better than mine, I was trying to say the same thing. Sorry if I confused anyone.