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PDWA rebuild

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77MidgetMkIV

77MidgetMkIV

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Hello again,
Whilest attacking my brakes, I have noticed a small amount of fluid sweating out of the warning switch seat in the PDWA. I am figuring that I should rebuild this and replace the switch while I am replacing everything else. Has anyone worked on their PDWA and/or used the repair kit from Moss?

thx in advance
 
I attempted to cross that bridge when I overhauled my brakes last year. The nut at the end that you have to remove is both large and probably frozen, based on other accounts I have read. Mine absolutely refused to come loose, and I only succeeded in making a flat spot on one of the brass unions. So, I just cleaned it out as best I could, made sure it didn't leak, and made sure the plunger moved and tripped the switch when I put some air pressure on it. Unless the switch is not working, it's probably okay. The two seals on the plunger are supposed to keep the space where the switch is dry, so yours apparently need replacing. Good luck!

Oh, and since yours is of the same vintage as mine, I discovered the PDWA in my car was a little different from what the service manuals say. Apparently, if the plunger moves and trips the switch, it latches that way unless you unscrew the switch body from the PDWA and let it snap back. The plunger in mine had a raised ridge in the center, as opposed to a groove as the service manual showed. Since the sides of this ridge are flat and the switch pushrod is also flat, it couldn't snap back in place. Might be good to know if you follow the manual procedure for brake bleeding. I used a vacuum bleeder so the PDWA wouldn't activate. The pictures in the service manual show a plunger that has a groove with tapered sides.

-Dave
 
Hi,
Never used the repair kit from moss, but the rebuild is pretty straight foward. i purchased o-rings localy and made a new copper washer. As is noted above if the switch trips then you have to remove the switch to reset it. Good luck

mark
 
thanks Mark/Dave,
Just wanted to reassure myself that there wasn't something secret about these things. Good tip on the switch reset. My cousin just did the one in his TR4, and had good success, so I figure as long as I can get the end nut off I will be OK. I am going to try and take it out/apart tonight, so I will let you know how it goes.
 
Well, the PDWA is sitting on my bench now, and so far you are both batting 1.000! The end cap is frozen, and the plunger is ridged, as opposed to grooved. Since I have bled my brakes a few times on the assumption that I didn't need to pay any mind to it, I was a little ticked at my manual. Then I looked at the switch and realized that the connection terminals were rusty dust inside the connector, so the light would never have worked anyway. Also, the rear brake line connection did not look like it was getting much fluid/if any, which may explain why my rear brakes were a little messed up. So it looks like I need to get this end cap off and refit some new seals/inspect the bore. Talking with my cousin last night gave me a couple ideas, as he just did the one in his Triumph. Any suggestions from someone who successfully "unfroze" the end cap would be great. Right now I am thinking of making a "mold" out of wood that it will fit tightly into, and bolting that to my workbench. The wood is softer than the brass, and should provide a warning crunch before the brass disfigures. With the PDWA mounted in it, I will apply a little heat, and try to free the bolt. I am hesitant to use too much heat, but since the assembly is brass and the end cap is steel, and brass will take the heat quicker, even a small delta should expand the brass a little, and hopefully I can then free it with a wrench/wooden mallet combo.

Silent- was in the HW store last night getting some denatured alcohol for cleaning the parts and found a wide assortment of O Rings! As long as the rubber is OK to use in a brake system, I should be good to go!

stay tuned.
 
Glad to hear it is a brass one. You should be able to free it up easier than if it were a steel one. You may find the wood will give to much when trying to free the end nut but with a little heat you shouldnt have too much of a problem. i had to purchase my orings from an industrial supplier and have had no problems with them, i still have a whole bag of them. so if you or anyone needs some let my know


mark
 
SUCCESS!!!!!!(I love the stooges)
I routed out two 2 lengths of 2x4 creating a pocket when put together that was a snug fit for the pdwa, and a channel for the switch seat, so that the unit couldn't move. I then clamped the jig to a really immobile object, a support column in my basement. managed to get it free on the "test run" for the jig, with no heat at all! From what I can see in the unit, it is in good shape, though the rings look a little worn. When running my finger across them, they don't even move, indicating that they do not stand proud of the groove at all. in addition, moving the piston around a little created some moisture in the middle supposed dry region. The bore looks great so far, though it has a date with some denatured alcohol tonight. Heading up to McLean's (Britbits.com)in NH tomorrow with my cousin to pick up one of his TR4's rear axles. Shot in the dark but he might have some O-rings. If not, we might be able to reach an accomodation for a couple of your spares, Mark.

Next step: putting all these $%^%ing parts back in, aka, the fun part. For now, a celebratory beer! /ubbthreads/images/graemlins/thirsty.gif
 
Great! Glad to hear you got it apart. Sounds like i spoke too soon about the wood. pretty clever to rout it out and all. it goes together pretty easy with a little brake fluid on the orings. if you cant find them i can mail them to ya


mark
 
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