Thread: Out With The Old.

Sorry not quite following. As I understand it you have replaced the shuttle valve that isolates one of the two brake circuits if one has a failure with a junction that does not do this.

So now if you have a loss of fluid in one circuit you also loose it in the other circuit.

What am I missing here.

Good evening.
All the shuttle valve does is activate a switch to warning light in cab.
It DOES NOT isolate the leaking front or rear circuit, which is separated only by 2 small 'O' rings and if they leak or the shaft is pitted the system becomes one, or it leaks out through the plastic switch. When one circuit is lost, on braking the pin moves the opposite way, as no resistance, plastic switch pin rises and Dash light comes on.
The reservoir is separated for front and rear, so If one circuit leaks it will drain the fluid, but you still have fluid for the other.
If you loose one circuit you will know. The peddle goes a lot further down.
Plus harder to bleed the brakes with it fitted.
Pic of internal part.
Can take more if needed

whitehillbilly

Ok - your understanding of how it works is different to mine.

Originally Posted by whitehillbilly64

Good evening.
All the shuttle valve does is activate a switch to warning light in cab.
It DOES NOT isolate the leaking front or rear circuit, which is separated only by 2 small 'O' rings and if they leak or the shaft is pitted the system becomes one, or it leaks out through the plastic switch. When one circuit is lost, on braking the pin moves the opposite way, as no resistance, plastic switch pin rises and Dash light comes on.
The reservoir is separated for front and rear, so If one circuit leaks it will drain the fluid, but you still have fluid for the other.
If you loose one circuit you will know. The peddle goes a lot further down.
Plus harder to bleed the brakes with it fitted.
Pic of internal part.
Can take more if needed

whitehillbilly

I don't think that is quite right mate. When a circuit has a leak, the piston moves in the cylinder and blocks off the outlet at that end, sealing off the leaking circuit. The moving piston also triggers the brake fail switch.

If you're too aggressive bleeding the brakes I've had the piston move and seal off the brake trying to be bled. You have to remove the switch and slide the piston back to the middle position to get flow back to the brake being bled.

Cheers,

Could it fail a roadworthy if you've changed it from dual circuit to single circuit brakes ?

I'm not sure if dual circuit is compulsory after a certain date of manufacture.

Colin

Hi Colin.
Still a Dual Brakes. Front fed by one half of reservoir, the rear by the other half.
Hopeful these pics will explain why the 5 port Girling PDWA valve does not close off leaking circuit.
Two port for Rear brakes. Shaft size compared to plastic yellow slotted bush.

whitehillbilly

The 3 port for front brakes.
The Drill bit was slid up into the Bore where the shaft moves. It is a slightly loose fit so smaller than actual bore, but closest I had. As can be see when 3 in 1 oil was pored in with the shaft slid forward to Apparent close circuit position, brass bush a 'O' ring fitted, the oil flowed out the other two ports.


whitehillbilly

G'day All,

Interesting thread!.

Found this article with diagram and pictures that explains how a similar PDWA operates. (It is a switch to display a warning light to indicate a failure in a pressure circuit.)
Triumph Pressure Differential Warning Actuator

Chris.