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TR6 PDWA switch TR6

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tr6web

tr6web

Jedi Trainee
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Well, I'm half way through redoing everything in the area of the firewall (Brake MC, Clutch MC, and stripping and painting the firewall). Boy did it need that - so much crap from the years. Looks nice now! Anyway, I noticed that the wire running from the harness to the PDWA switch wasn't even connected because it's broken. I guess I can replace the "cap" that goes into the switch. But, after reading the repair manual, it goes into all of this detail on how to reset the switch. Any suggestions?
 
It may not be just the switch thats failed. As you can tell from the manual, there is a little shuttle gizmo that moves if the rear break pressure is different to the front. I suspect this shuttle is suseptable to getting seazed and the seals to leaking. Mine has the switch removed and the switch appature capped. When rebuilding the brakes I stripped it down with the intention of rebuilding it and reinstalling the switch. I soon found the best thing to do was to leave it well alone - the shuttle seals were leaking and there are no repair parts for this unit and a cast steel replacement is around $200! Not sure what other people's experience is, but I suspect this is the most common solution to dealing with the PDWA. It looks like it could be a common source of leaks (the switch itself will not hold pressure - the seals on the shuttle do that and so far as I know there are no replacement parts for these. Also I do not think this is a safety issue - it is pretty easy to tell if you have a failed breaking circuit.

Rob.
 
Thanks. The other question is whether or not it even works. There are no leaks coming from it...I just want to see if I can hook it up and try to reset it.
 
You can rebuild the PDWA using Ethylene Propylene (EP) O rings from a local hydralic supply house. See this page for "instructions" PDWA Re-Build
 
[ QUOTE ]
I soon found the best thing to do was to leave it well alone - the shuttle seals were leaking and there are no repair parts for this unit

[/ QUOTE ]
If you are fortunate to have the 5/16" cylinder shuttle that uses O-rings, you can buy O-rings that are 3/16" ID & 5/16" OD with 1/16" cross section (size # 008). Make sure you specify ethylene propylene (EP/EPR/EPDM) ring material. McMaster-Carr should have them. The other shuttle design uses cup seals similar to those in the brake MC and are NLA to the best of my knowledge.

Recentering the shuttle is easy: either push/pull it with an awl through the switch port OR open an opposite-circuit bleed nipple and slowly mash the brake pedal.

Rick O.
72 TR-6
 
Again, thanks, Rick. I didn't know it had all of these "O" rings. Maybe it does leak. I'll have to take it apart to see.
 
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