brake pressure switch assembly

[tr-lee]

Not sure what the actual name is of the switch assembly mounted on the driver's right inner fender. You know, has the 5 brake lines running to it. Mine is brass but I think they made them in cast iron also.
Anyway, mine was leaking out the switch so I ordered a rebuild kit. When I took it apart I realized it had different seals than the kit. When looking it my 2 Spridget workshop manuals I can see that the kit it probably correct but it's my part that is different. Instead of using O-rings for seals, mine has actual cup seals like a master cylinder. The O-rings certainly don't fit.
My car is a 72 Midget & 69 Sprite combined so I'm not exactly sure which car it came off of. Has anyone seen one of these with cup seals? I suppose it's possible that this part may be from some other Brit car that was swapped some years back.

It's a stupid little part to be holding me up from getting out to enjoy the weather. I guess I could bypass the whole thing with some fittings.

Let me know if anyone knows anything about this part. Thanks.
Lee

 

[dklawson]

About a year ago I found a good web site discussing this valve. (I'm sorry... I didn't save the link). On that site the author was discussing the same problem. He ordered o-ring seals compatible with brake fluid (EPDM ?) and lathe turned a stainless steel piston/shuttle to accept them. This allowed him to keep the proper brake performance and plumbing. If I can find the link again I'll post it here. However, the author may have taken down his site. I remember him including lots of caveats about making your own brake parts, using the right seals, etc. He may have decided it was too risky to leave that information on the web lest he be found liable for someone's brake failure.

 

[tr-lee]

Ah, a fellow North Carolinian. Thanks for the reply. At least I know I'm not crazy. Sounds like I may be looking more into the bypassing the whole thing. What is it's purpose anyway? Is it to tell you your backs need adjustment or tell you that one system has failed (no pressure)? I would think regular maintenance would cover the first possibility and the second .... seems to me it would be pretty obvious. If I can find the parts quickly I'll put it back together and post where I found them.

Thanks,
Lee

 

[dklawson]

I hadn't noticed you are in Hickory. I have family just a little ways from you in Taylorsville.

I'm not sure what the purpose of that valve is. I've never had a car with one on it. I thought it was there to tell you when part of the dual brake system had failed or lost pressure.

I seem to remember finding several links on the web about the implications of (and how to) bypass this valve. Try a litte bit of googling and let me know what you come up with.

 

[77MidgetMkIV]

The name of the little $%#@ bit is the P.D.W.A., or Pressure Differential Warning Actuator. Dk is correct: its purpose is to trigger when there is a pressure drop in either of the hydraulic lines servicing your brakes, and activate the brake warning light that is in the dash of your car. When there is a pressure drop, it will be on one side of the piston or the other. The difference in pressure will move the piston. When the piston moves, it activates the switch plunger that rests on the piston under normal pressure situations. I just removed mine from my 77 midget. I have the O-ring type, but even mine is different from the description in the repair manual. I have also given some thought to bypassing it, but in the end, since mine was in good shape, I plan on refitting new O rings. When bypassing, you will need to deal with the fact that you have 2 feeds from the M.C. feeding into 3 brake lines (at least, that is the case on the '77). This is because each front caliper has it's own feed. It might be easier for you to just find the correct deals and rebuild. I am sure that there is someone on this board who has seen one with the cup rings, though I have not.

Good luck!

 

[trrdster2000]

For those who have the O ring type here is the best repair article I have found. Wayne
https://www.vtr.org/maintain/pdwa.shtml

 

[tr-lee]

Thanks guys. I spent a good bit of time search Google last night and not finding anything. I'll do a little more searching on the PDWA this time. I figure one straight union for the rear lines and a T for the fronts would work. I know the light on the dash is supposed to light but I've never seen any of my cars actually work for even the test. Wiring or bulb I'm sure but just never found it. I'm not arguing against fixing it but I see very little value in it's function. If it tells you you have no rear brake pressure.... ok, you've got a couple shots of brake before you probably drain you reservoir. It it's the fronts, well I think you've already figured out that you had no brakes when you stepped on the pedal.

Are these brake fittings some oddball thread? I can't remember what the deal is about Whitworth(sp?) fittings and Brit cars.

Hey, I suppose I've got a rebuild kit if anyone is interested. /ubbthreads/images/graemlins/smile.gif It comes with 2 sets of O-rings for different style shuttles.

I'll post something if I can find where someone has a good bypass suggestion. All I've found so far is other people looking for the same answer.

Lee