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Steve i know you replace the PDWA valve with a 3 way union,would this work , just remove the shuttle valve from inside the PWDA unit ?
Dave
As Jeroen says, removing the shuttle will allow the 2 circuits to effectively become 1 as fluid will flow across the space formerly occupied by the shuttle. Which kinda defeats the purpose of having dual circuit brakes!
There is also the fact that the silly PLASTIC switch will come under fluid pressure from the brake system (Around 2000psi) which will blow it out like a bullet from a gun and result in total brake failure.
A 3rd factor that I've only experienced on Bob's car, is that, even though the shuttle was stuck in place, there must have been some damage to the internal seals as I did find some fluid behind the switch where there shouldn't be any! This could result, as and when this internal leak got worse, in the situation above arising. A brown trouser moment in the making if ever I saw one!
So, in conclusion, better, safer, easier and cheaper to delete the PDWA. It's a complicated, unreliable and inefficient solution to a problem that doesn't really exist. The very fact that they were only fitted to ANY car for a handful of years in the late 70s and early 80s PROVES this beyond doubt, if they were any good, they'd still be in use!
A fluid level sensing cap on the master cylinder (which IS still used today) gives earlier warning of impending failure, cannot possibly affect brake performance by any failure within it, has NO effect on ease of servicing the braking system and doesn't need to be "set up" every time brakes are bled. Finally, in production terms, it's massively cheaper than the PDWA!
My personal opinion is that it was an early attempt by Girling to satisfy a piece of proposed legislation (possibly in the USA) that never actually got adopted. No other major brake company produced anything like it, though some ATE systems of the same period (Notably VW, who also invested heavily in the US market) had similar sorts of pressure switches built in to their dual circuit master cylinders. Again these were only fitted to vehicles built around the same time period when the PDWA was current.
Steve