brakes

[slowboy]

can someone please kickstart my brain, what was the compensator to use,or the mod to the compensator to get slightly less braking at the rear, or am I imagining ?? thanks

[GraemeC]

Shorter/weaker spring in the subframe mounted valve?

[slowboy]

Shorter/weaker spring in the subframe mounted valve?

was that it graham.? and bigger bore rear cylinders ? cant remember ,

[GraemeC]

Thought it was smaller cylinders -1/2" ones.
Then shorten the spring and drill and tap the valve to make it adjustable.
Without shortening the spring you can only increase the effort with an adjustable valve - it's effectively a spring balanced poppet valve, once the spring pressure is overcome by the line pressure it locks off, weaker spring means it locks off sooner.

[slowboy]

Thought it was smaller cylinders -1/2" ones.
Then shorten the spring and drill and tap the valve to make it adjustable.
Without shortening the spring you can only increase the effort with an adjustable valve - it's effectively a spring balanced poppet valve, once the spring pressure is overcome by the line pressure it locks off, weaker spring means it locks off sooner.

that's it, the light has come on! was that you passing the shrimp boat project earlier ??, are you in pub later, cracking band on

[GraemeC]

Shrimp boat project? You've lost me with that one!
Not out playing tonight - who's on? You about tomorrow, might need a small job doing......

[slowboy]

Bolton le sands at lunch time, up the top, sure it was you pipped, me old man is helping his mate restore a turn of the century Morecambe bay shrimper in the yard where I was parked, band of gypsies in the royal, and try me tom mate on text , don't know when or where or who

ps, thanks for the brake info

[GraemeC]

Nah, not me - been down on't rollers today.
Good band, shame we've missed 'em.

Will be in touch.....

[WNX700H]

Jon,

Not sure which wheel cylinder size is optimal for use with an adjustable valve but would suggest wheel cylinders used on std 1275GT or S with 10" wheels, think they are 0.625" in diameter. If you have the largest cylinders then as mentioned with the same compensator then converted to adjustable with same internal spring you will only be able to increase the line pressure at which the valve shuts off. I am about to determine this myself on a car I am currently building, will play around with wheel cylinder size and let you know.

Smaller wheel cylinder diameter = lower braking force for a given line pressure and shortest pedal travel

But in setting the brake balance careful choice of friction materials is necessary to try to have materials front and rear that have similar fade characteristics so as you put more energy into the system and the temperatures increase , the brake balance is not affected by either front or rear brakes fading first. Failure to do this can create more problems, for example using a rear material that fades quicker than the fronts will not cause stability issues but will result in most of the work being done on the front axle giving higher temps .... vaporisation of fronts etc ....... ie you are not making the most of the braking you could get out of the rear axle as the material has faded.
Setting the brake balance for a road car is best done on dry tarmac which generates the highest decels and hence causes the largest weight transferance rear to front. You want to have the rears just before lock with the fronts having locked in order to maintain stability.

Also tyre choice plays a factor as with using tyres that can pull higher decels before locking up such as Avons the weight transfer off the rear axle will be greater.

All this make sense? .... brake sytem design is my field having worked for Girling for 31 years.

['S'-type]

I think there have been three different types of rear brake pressure 'compensator'.

Early single line type (cylindrical) spring type based on fluid pressure alone, later inertia type based on rate of transfer of load from rear to front during decelertion (squarish shape) incorporating a rolling ball - both rear subframe mounted, and from 1978 the dual circuit version mounted in the engine bay.

The first of these is the one that can be converted to an adjustable type or simply reduce fixed spring pressure by shortening. The performance charcteristics of second one apparently depend on the angle at which it is mounted. Progressively dropping the front of the valve reduces braking on the on the rear. I don't know about the third one.

Vizard's How to modify book page 173 covers these mods.

The first two do seem available but for mega money on US site Minimania. So Lets hope we saved those crusted up ones removed during subframe swaps in years gone by.

I agree smaller bore cylinders will help achieve reduced rear wheel braking pressure all other things being equal.

Apolgies if you knew this already.

[slowboy]

great info fellas, thankyou