Poor brakes with no feeling

[Stuart Giles]

In my experience, poor hydraulic brake performance is a result of a too large bore in the master cylinder and/or too little mechanical advantage on the pedal; i.e. if the master cylinder pushrod is halfway up the pedal you will need to be superman to generate the 1000 PSI+ line pressure that hydraulic brakes need to work well.

[Howard Wright]

Hi Shane

Have the brakes become like this or have they always been so?

I ask because when I first set up the hydraulic brakes on my first special I found that it was difficult to get enough travel on the master cylinder push rod acting on the MM cylinder. That meant that there just wasn’t enough fluid movement to activate all the wheel cylinders.  The pedal felt very woolly and I couldn’t get the wheels to lock. The answer was to fit a larger master cylinder.

With hindsight I now wouldn’t fit hydraulics as getting them set up correctly took me ages.  Cable brakes are relatively easy to set up and when they are work perfectly adequately.....AND uncoupled I think give more control of braking.

Cheers

Howard

[Ruairidh Dunford]

At rest, does a small gap exist between the actuator rod (usually attached to the pedal on A7 conversions) and the master cylinder plunger?

[Zetomagneto]

Yes Howard, you can do a handbrake turn using the footbrake!

[Stuart Giles]

Yes Howard, you can do a handbrake turn using the footbrake!

The OP would probably also be able to do a "handbrake turn" using the footbrake if the front brake backplates have been fitted on the wrong sides as suggested as a possibility by Charles P in post number 8. 

On the other hand, such a twin trailing brake setup would give superb braking when you reverse the car

[Rogerfrench]

I don't think I was alone in finding that 2ls hydraulics gave too much braking, admittedly with the tyres of 50 to 60 years ago.
On both the Ulster rep that my father and I raced in 1973, and my own special, I cut the leading 1/3 off the front brake shoes and still had plenty of stopping power with much less risk of front wheel lockup.
There was a 750 formula racer who was pleased with his brakes until someone pointed out that he had inadvertently installed them as trailing. However, he didn't "fix" them, but continued to be pleased! I wish I could remember his name, I think my father referred to him in one of his 750 Bulletin contributions long ago.

[Ruairidh Dunford]

When I put my father’s RK back on the road about 10 years ago it became clear that the car had been set up trailing since it was converted (not by him) in the late 1950s.

Prior to this coming to light my father was very happy too!

I converted it back to uncoupled cables about 5 years ago because the lack of use it now gets meant seized cylinders were a regular occurrence.

[Tony Press]

I don't think I was alone in finding that 2ls hydraulics gave too much braking, admittedly with the tyres of 50 to 60 years ago.
On both the Ulster rep that my father and I raced in 1973, and my own special, I cut the leading 1/3 off the front brake shoes and still had plenty of stopping power with much less risk of front wheel lockup.

If friction is independent of the area of contact how does this work ?

[David Stepney]

Tony.
Consider a brake drum rotating clockwise, with a brake shoe running from 12 0'clock to 6 0'clock on the right hand side. If the actuator is at 12 0'clock and the shoe pivoted at 6 o'clock then, as the shoe contacts he drum, the drum will tend to pull the shoe in the same direction as it is rotating. Since the shoe can't follow the drum because of the pivot, it is dragged into closer contact with the drum, thus increasing the braking effort. This is known as 'self-servo' action. If the shoe is on the left of the drum (i.e.running from 6 o'clock through to 12 o'clock) but pivoted at 6 o'clock and actuated at 12 o'clock, then the rotation of the drum will have an opposite effect and try to push the shoe away from the drum, reducing the braking effort.

Hope this helps.

[Tony Press]

I was referring to the report that- 

'I cut the leading 1/3 off the front brake shoes and still had plenty of stopping power with much less risk of front wheel lockup.'

This shouldn't have any effect on the braking effort leading or trailing should it ?