PDWA Valve - an anatomy

[dasadrew]

As this is a subject which turns up now and then with questions, I thought it might be of use to take a picture of the PDWA valve in the braking system. This valve is from a 1974 Mk2 Stag.

The "dumb-bell" steel part is the shuttle valve spindle, with two 'O' rings on it having been replaced. The repair kit comes with two large and two small 'O' rings. At least on my valve, it was the two large ones which were needed. The two small ones are discarded - maybe they are for a different valve or production year.

The switch with its brass plunger can be seen top right. As the shuttle valve is displaced due to a brake fluid leak on one side, the conical flank in the centre of the shuttle valve spindle depresses the brass plunger and this lights the warning light.

The blue tube is Ate Brake Grease which is safe to use for reassembly of components which come into contact with brake fluid.

The copper sealing washer on the shuttle valve blanking plug is also included as part of the overhaul kit.

The screw on the bottom left is a home-made tool from a filed down UNF bolt and which has the same basic dimensions as the switch. It screws in in place of the switch and keeps the shuttle valve spindle centred during brake bleeding operations.

Brake fluid is only outboard of the rubber 'O' rings on the shuttle valve spindle, so the switch can be removed without fluid loss or bleeding being necessary. If fluid dribbles out of the switch area, then this is an indication that the 'O' rings need replacing.

The nut and bolt with washers is simply the attaching bolt which fixes the PDWA valve to the inner wing - at least on a LHD Stag it does!

Happy PDWA overhauls!

IMG_2967 (Custom).JPG

[jleyton]

Excellent Drew, many thanks.

It's so simple but it's so useful just to know exactly how it's made up.

Cheers

Julian

[Duncan Skye]

There's some very good points in your descriptions, Drew.

Now I don't wish to push you into anything, but I think I remember reading some info somewhere about resetting that valve after it's tripped - some sort of sequence involved? I've struggled with it whilst priming a dry system and didn't really know what conditions I was trying to overcome as one half of the system wouldn't prime. Sheer dogged persistence on the pedal paid off in the end, but if you knew anything about how to avoid that, or on re-setting the valve, perhaps Carl would accept it as an article for the new 'How To' Section?

With best wishes and many thanks,

Duncan, Skye

[jbuckl]

If the valve appears to have been activated to one side, disconnect the wiring connector, unscrew the switch, lean over with a torch to see inside the valve.
Use an electrical screwdriver to centralise the plunger.

Screw the switch back in and dont forget the connector.....how many burnt ones have you spotted!

[elvimto]

When did my brakes the first time I use a hand vacuum pump attached to the bleed nipple it pulls the fluid into a small plastic cup it worked great then a final pedal bleed got really good results.

[ukbiggles]

Hi Drew

Really useful to see it broken down like that. A picture is worth a thousand words as they say.

MY PDWA has a bolt instead of a switch so the whole thing is ineffective. Have acquired another PDWA, but my next problem is finding the wiring that goes to the switch on the PDWA. I guess the PO has cut the wires off the loom. So my problem is how to wire the switch in again - and to what?

Any ideas anyone?

Regards

Gord

[Rubce]

Hi Drew

Have acquired another PDWA, but my next problem is finding the wiring that goes to the switch on the PDWA. I guess the PO has cut the wires off the loom. So my problem is how to wire the switch in again - and to what?

Any ideas anyone?

Regards

Gord

Gord

Bring your car round here and I will sort the PDWA wiring for you.

Bruce

[Dieter H. Marschall]

Hello Drew,

This home-made tool from a UNF screw is a great idea. I hope you do not mind, if I simply copy it...? I am prepared to pay your royalties in form of a drink!

Best wishes,
Dieter.

[dasadrew]

Go ahead Dieter - I copied it too!

(I'll still accept the drink though!)

[Klaus Schlueter]

Does this picture help Dieter?

DSC03117.JPG

Klaus

[Dieter H. Marschall]

Hello Klaus,
How did you do it? Did you file a 3/8" screw down to 3mm (as Drew did it) or did you drill a 3mm hole into the screw and glue in a 3mm pin?
Kind regards and thank you for your help,
Dieter.

[DJT]

Hello Klaus,
How did you do it? Did you file a 3/8" screw down to 3mm (as Drew did it) or did you drill a 3mm hole into the screw and glue in a 3mm pin?
Kind regards and thank you for your help,
Dieter.

I posted this last year. http://www.stag.org.uk/forum/showthr...highlight=tool The way I made it is someway down the post.

Dave

[ukbiggles]

Hi Bruce

That's a very generous offer. I've be very happy to take you up on it. Will PM to fix a time.

Cheers

Gord

[Klaus Schlueter]

Hello Klaus,
How did you do it? Did you file a 3/8" screw down to 3mm (as Drew did it) or did you drill a 3mm hole into the screw and glue in a 3mm pin?
Kind regards and thank you for your help,
Dieter.

No Dieter, I did not file it down to 3mm. That would have been a typical task ages ago during my apprenticeship.
I used my little lathe and turned it down.

Regards Klaus

[Dieter H. Marschall]

Hello Klaus,

Thank you for the info. Although I own a lathe, I am not (yet) able to operate it. So I guess I will tap a 3/8" srew for a 4mm screw and then file that one down to 3mm.

Best wishes,
Dieter.