Author Topic: Pressure Difference Warning Valve (PDWV)  (Read 1590 times)

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Offline 3929R

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Pressure Difference Warning Valve (PDWV)
« on: Thursday,February 04, 2016, 07:31:16 AM »
The PDWV (part 7 on the diagram below) triggers the brake fail warning light on the dash. Mine has not worked since I rebuilt my brakes (removed boosters and installed new Datsun MC, slave cylinders, and flex lines). At the time I followed the directions below with no luck what so ever. My dash light would not go out unless I unplugged the PDWV. So I've been driving with it unplugged. My car had been stored for years and I've no idea if the switch worked before I did the brakes.

I'm wondering if the plunger/switch is stuck?
Any other ideas on how to free it?
The valve is high in the system, could it have air trapped? Can it be bleed?
Can the valve be removed and cleaned or rebuild it?
Other than a glance at RD's page, I haven't looked for the part yet. Anyone know if it is available or what other cars use the same part?
How high of a priority should I make this? Shouldn't I feel a problem that would trigger the valve? (I hadn't given it much thought till the other post with the brake light switch for sale.)

1.   Bleed the rear brakes FIRST, commencing with the left-hand wheel, then bleed the front brakes starting with the left-hand wheel - ALWAYS the wheel nearest to the master cylinder first, whether front or rear.
2.   Use only a light pedal action and DO NOT push the pedal through at the end of its stroke.
3.   DO NOT 'try' the pedal until the system is fully bled, as either action will cause the plunger to move and actuate the brake fall warning lamp.
4.   If, during the bleeding procedure, the plunger operates the switch and the warning lamp is 'on', the bleed screw must be closed and the bleed screw at the other end of the car opened - if bleeding the front brakes, open the bleed screw on a rear brake and vice versa.
5.   A steady pressure must then be applied to the pedal until the lamp goes out, when the pressure must be released immediately and the bleed screw closed, otherwise the piston will move too far in the opposite direction and require resetting again.
6.   When the lamp goes 'out' a 'click' will be felt on the pedal as the piston moves back.
« Last Edit: Thursday,February 04, 2016, 07:34:37 AM by 3929R »
Mark
Salt Lake City, Utah, USA

Offline RoddyMac

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Re: Pressure Difference Warning Valve (PDWV)
« Reply #1 on: Thursday,February 04, 2016, 07:43:21 AM »
If it's anything like the MGB ones (and it should be somewhat similar), you can remove the switch from the block and manually move the piston inside back to center.  Or, if you can find a bolt with the same thread as the switch, grind or turn it to a point and install in the block to keep the piston centered (though only use it for bleeding purposes).  You used to be able to get the o-rings for the MGB PDWV, and to replace them the easiest way was to remove the whole thing from the car, then while you have it on the bench (or wherever) remove the large hex bolt/cap at the end and pull/remove the piston from the block, remove and replace the o-rings then reassemble.  But, I don't know if the o-rings are available for the PDWV used on the Europa, you may have to crack it open and measure.  One other thing, the switch should be dry, if it isn't then the o-rings have failed.

Edit:  I had a quick look on the interwebs, and the late Spitfire one looks very similar, knowing that both Lotus and Triumph used Girling parts, they may be the same but I can't confirm this.
« Last Edit: Thursday,February 04, 2016, 07:46:30 AM by RoddyMac »

Offline BDA

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Re: Pressure Difference Warning Valve (PDWV)
« Reply #2 on: Thursday,February 04, 2016, 09:42:27 AM »
I don't have much to add other than I always heard that you should bleed the brakes furthest from the M/C first which would mean you would start with the driver's side front caliper first.

Offline Grumblebuns

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Re: Pressure Difference Warning Valve (PDWV)
« Reply #3 on: Thursday,February 04, 2016, 12:00:50 PM »
Mark,

Take a look at the Buckeye Triumph site for an article on overhauling the PDWV valve. It may be of some help.

http://www.buckeyetriumphs.org/technical/Brakes/MCPDWA/MC.htm

Joji Tokumoto
Fallbrook, Ca


Offline jlmullen2

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Re: Pressure Difference Warning Valve (PDWV)
« Reply #4 on: Saturday,February 06, 2016, 08:04:00 PM »
Mark:

I'm in the process of removing the boosters on my Twin-Cam and Joji helped with how to route the remaining hard lines as I'm planning on keeping the PDWV. As part of the research I just Googled the Girling part number on the PDWV valve to see if I could get a new one if needed. The exact part number is used on quite a few cars, including  Ferrari. I ran across a message board where used PDWV's were selling for $175.
Larry Mullen
73 Europa TC Special
97 Saleen 281
04 Subaru WRX

Offline jbcollier

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Re: Pressure Difference Warning Valve (PDWV)
« Reply #5 on: Saturday,February 06, 2016, 10:59:50 PM »
+1 on being able to manually reset the valve by removing the switch and using a very small screwdriver to side the shuttle back into the middle position.  IIRC, once the shuttle has moved to one side and activated the switch, the switch plunger prevents the shuttle from moving back so you have to centre it manually.

Personally I would toss the darn thing and fit a brake fluid reservoir level switch instead.  Better to know before one system fails that have a light that comes stating what is obvious by the fact the pedal is now much lower and the brakes less effective.

Offline 3929R

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Re: Pressure Difference Warning Valve (PDWV)
« Reply #6 on: Tuesday,February 09, 2016, 09:49:57 AM »
Thanks for all the replies. This remains on my to do list but is still below replacing my selector shaft seal and bush. It won't be too long before my wrenches aren't so dang cold to touch. Once it warms up a bit, I think I'll pull the switch, check the seals, manually reset the valve, and decide to go from there.
Mark
Salt Lake City, Utah, USA

Offline espurin

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Re: Pressure Difference Warning Valve (PDWV)
« Reply #7 on: Tuesday,February 09, 2016, 01:31:15 PM »
I rebuilt few years ago.  If the ring seals are good condition, it may work.   

Offline Arizona

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Re: Pressure Difference Warning Valve (PDWV)
« Reply #8 on: Tuesday,February 09, 2016, 07:38:23 PM »
Personally I would toss the darn thing and fit a brake fluid reservoir level switch instead.  Better to know before one system fails that have a light that comes stating what is obvious by the fact the pedal is now much lower and the brakes less effective.


I'll second that. I tossed mine 40 years ago; never missed it.
George F. Johnson

Offline Bainford

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Re: Pressure Difference Warning Valve (PDWV)
« Reply #9 on: Wednesday,February 10, 2016, 10:29:36 AM »
Personally I would toss the darn thing and fit a brake fluid reservoir level switch instead.  Better to know before one system fails that have a light that comes stating what is obvious by the fact the pedal is now much lower and the brakes less effective.


I'll second that. I tossed mine 40 years ago; never missed it.
Yup, mine is going when I embark on my brake system refit.
The Twin Cam plays the symphony whilst my right foot conducts the orchestra. At 3800 rpm the Mad Pipe Organ joins in.

Trevor

Offline 3929R

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Re: Pressure Difference Warning Valve (PDWV)
« Reply #10 on: Tuesday,February 16, 2016, 07:45:41 AM »
Mark
Salt Lake City, Utah, USA