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 Posted: 08-29-2017 10:10 pm
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Dick Fickey
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Dealing with a North American Safety device, the Pressure Differential Warning Actuator. Just finished the car and the brake fail light stays on and brake fluid is leaking out of the switch. The PDWA is one of the few parts I did not rebuild. Assumed that in bleeding the brakes that it moved the piston to one side or the other and grounded the light through the switch. However when I disconnect the wire on the switch the light stays on so in trying to follow the wiring diagram it would have to be the handbrake warning light switch. Is this assumption correct? Other question is why are there two wires from the PDWA switch to a common junction on my other JH and on this car only one wire in the harness? The connector for the switch is not in good shape. Does anyone have a good one off an old harness?

I removed the PDWA and was going to order a rebuild kit. On inspection it looked like there was corrosion in the bore so decided to order a rebuilt one from Delta Motorsports. Should have it today but need three days to repaint the area the fluid leak bubbled the new engine compartment paint.

When I get the new PDWA installed what is the best procedure to bleed the brakes to prevent moving the piston. I will feel a lot safer with this working going 70 mph when my brake pedal goes to the floor and the little light tells me that my breaks have failed. They could have used a buzzer then I would not have to look down.

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 Posted: 08-30-2017 02:44 am
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Esprit2
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Dick,

When you open one hydraulic circuit to bleed it, the PDWA's internal shuttle/ piston will move off to one side, closing the switch contacts in and illuminating the warning light. Then when bleed the second circut, the shuttle will move back the other way, turning off the warning light as it passes center. Finally, as it continues to the opposite extreme, it will once again close the switch contacts, illuminating the warning light.

When you're done bleeding the brakes, no matter which circuit you end with, go to the opposite circuit one last time just to center the PDWA. Open the bleed valve just a little, and slowly bleed out a little fluid until the warning light 'just' goes out... stop! The shuttle is now centered.

Regards,
Tim Engel

Attachment: PDWV - Pressure Differential Warning Valve - Cross-Section Drawing.jpg (Downloaded 42 times)

Last edited on 08-30-2017 02:47 am by Esprit2

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 Posted: 08-30-2017 02:55 am
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Dick Fickey
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Thanks for the help Tim. Will follow your instructions when I bleed the brakes. Just got the rebuilt PDWA but I have to first repaint the area that the leak ruined.

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 Posted: 08-30-2017 03:12 am
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Esprit2
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Dick Fickey wrote:
Thanks for the help Tim. Will follow your instructions when I bleed the brakes. Just got the rebuilt PDWA but I have to first repaint the area that the leak ruined.Consider repainting that area with POR-15. It doesn't have the color selection of regular paints, but it's more durable than most paints. I can't swear to it's resistance to brake fluid (which eats most paints), but it is highly resistant to most chemicals.

Test-paint some scrap piece of steel, let it cure fully, then pour some DOT 3 or 4 brake fluid on it. That should give you a good idea of how well it will work. Let us know.

POR-15 is a cyanoacrylate, so the same basic recipe as super glue... just specialized for the task, with pigment added.

Like super glue, POR-15 is difficult to remove when you want to. Don't spill it on anything you care about, or get it on your skin (wear gloves, long sleeves and eye protection), or you may have a colorful 'scar' for quite some time. Unless you find that DOT 3 or 4 eats it.

POR-15 is also effective for gluing your jeans to your leg. 'Apply' to the outside, it soaks through, and presto.

Regards,
Tim Engel

Last edited on 09-03-2017 05:45 pm by Esprit2

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 Posted: 08-30-2017 07:26 am
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Frank Schwartz
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++It might be interesting to note that the European JHs do not have that valve at all. I have found that when one is not working, rather than buy a new one or struggle with a "rebuild kit", I just bypass the thing entirely. It does not affect the braking, only the signal light.

I think Bruce Madden has a way of just plugging the unit so you do not have to remove it, but I cannot remember how he doe sit..but it is quite simple.

It should be mentioned that the light is the same light that comes on when your hand brake is in the "up" position.

Frank

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 Posted: 08-30-2017 02:04 pm
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redracer
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Boy--you guys are up early!
I wrote about this over 25 years ago and had it published in the White Lady, our now defunct mag. for all Jensen owners.I believe I had it entitled "Another one of Nadir's stupid safety ideas"(or something to that effect). Our dual master cylinders had one side do front brakes and the other the rears, unlike modern cars which do diagonal pressure, i.e. left front with right rear, etc.. You can live and drive easily without the rears(I have), but not the fronts, and you will NOT need a light to tell you so. Plus, bleeding the brakes has sometimes "locked" the pins on one side or the other causing the light to always be on.
The "fix" is fairly simple and requires you(or friend) to have the small 1/8" pipe tap(27 threads/inch and NOT the British pipe of 28 threads/inch, which is what the oil pressure line fittings are). Remove both ends of the switch, remove the 2 sliding plugs and the small steel ball, then turn the tap 12-13 complete turns in each end(no drilling is necessary as the holes are the correct size to begin with!!). Using 2 brass allen plugs(takes a 3/16" allen wrench), wrap a little teflon tape on the "starting" ends of each plug and install, being sure none of the teflon is exposed in the chambers(snip extra off).
(if you can't find the brass plugs, I still have plenty)

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 Posted: 08-30-2017 03:19 pm
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Frank Schwartz
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That's it !! It all comes back in a blinding flash !!! Thanks, Bruce.....
So, to those who struggle with that gadget..go and do likewise...or rather, plug the crazy little thing as he instructs, and then forget about it....

Frank

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 Posted: 08-30-2017 09:14 pm
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Dick Fickey
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Thanks for the information. If I had seen Bruce's post before I ordered the rebuilt one I may have plugged mine. Will save that post for a future problem with my other car.

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 Posted: 08-31-2017 02:15 am
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Schorse
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That's good info. I also feel like this swith is not necessary.
Instead of risking to get some debris into your hydraulic system you can also use some thread sealant which is designed for hydraulic fluids (Loctite 545 seems to be but haven't used it)

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