TR6 PDWA Leak

[SherpaPilot]

I have been chasing a brake fluid leak in my 72 TR6. Fluid is seeping from the PDWA nylon switch and running down the frame. After purchasing a new switch, checking alignment of the internal piston and reinstalling, it continues to leak. I attempted to try a rubber "o" ring but that was a waste of time as it continued to leak. The leak is passing by the plastic threads and exiting near the top of the PDWA. I am guessing my next step is to remove the assembly and rebuild the entire unit. My question is this: I know I'm not the first person to experience this problem. Has anyone bypassed this poorly designed component in the hydraulic system? Could I simply install a brass plug and eliminate the electrical switch completely? Thanks in advance for any help you can offer. Yes, I have read most of the articles posted concerning rebuilding the switch but I'm thinking of removing it completely.

 

[TR3driver]

The problem is not the switch at all; the cavity under the switch is supposed to be dry. You need to replace the seals on the shuttle.

Yes, you can eliminate the function by putting a plug in the hole. I wouldn't, but obviously it's your car. I don't know for certain that a working PDWA would have kept me from flying down a freeway off-ramp with absolutely no brakes, but it might have.

 

[carpecursusII]

Easy job, you can't get seals for the original shuttles but moss sells a kit with a new shuttle.
https://www.buckeyetriumphs.org/technical/Brakes/MCPDWA/MC.htm

 

[dklawson]

I found that different cars use different piston/seal arrangements for the PDWA. The standard size o-rings did not fit the pistons and bores of the PDWAs I rebuilt. I had no option except to make a new piston following guidance on the Buckeye Triumph website so that the o-rings had sufficient "squish" to seal. Once I made the new pistons I had no more leaks.

If you decide to continue trying replacement seals, be sure any o-rings you buy are made of EPDM, not the more common Buna-N (Nitrile) material.

You could indeed make a plug to replace the switch. If you have access to a lathe, I would turn a point on the end of the plug to mimic the end of the switch. That point would prevent the shuttle in the PDWA body from moving from side to side.

 

[SherpaPilot]

Thanks for the info guys. I did not know that cavity was supposed to be dry. Now I understand that a rebuild is in order. Since this is the original unit from 1972 I think it is probably due anyway. I'll get right on this thing and hopefully be back on the road again soon. Again, thanks for taking the time to respond.

 

[mallard]

I just did this to my TR6 in the fall, it took about five minutes, bleeding the brakes after took a bit longer. Then follow the directions in the book to center the piston. Make sure you get the correct kit.

 

[Tybalt]

I rebuilt my PDWA many years ago using the Buckeyes instructions and EPDM O-rings purchased from MCMaster Carr. No one had a kit for them at the time. There were replacement units available at the time but they were cast iron instead of brass like the original and rather expensive. I had trouble getting the piston to come out even closing off the other ports and using compressed air. I hit it with some Aero Kroil and let it sit for a day, then tried it agin with the opening aimed at a cam I had lined with rags and foam. When the piston finally let go, it came out like a shot and was glad that i had aimed it at a container and that the container was lined with soft material to catch the piston. once everything was cleaned up, it went back together rather easy and went through the centering operation, rather easy if a bit tedious.

 

[dklawson]

After installing the rebuilt PDWA on our Spitfire I started wondering... what if we made a plug with a point on it to temporarily replace the switch during brake bleeding. If the point kept the shuttle from moving then there would be no re-centering the PDWA required. Just a thought.