• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Permanent fix for PDWA brake switch

Share this page

A

ALLAN

Jedi Warrior
Offline
After installing my new electrical brake switch on the PDWA it started leaking out the top of the switch right away, I sent it back to Moss for a refund, so here is my permanent fix that some of you might be interested in. It will not be for everybody--but it does work.

I removed the large threaded plug and pulled the plunger out of the PDWA housing and drilled the bore out to 23/64 down about 3/4"--I didnt go all the way through the bore -leaving a small shoulder at the bottom. I then tapped out the hole to 3/8" NF and screwed in an automotive allen head-set screw 3/8"x5/8"NF. I screwed it in untill it bottom out on the shoulder at the bottom of the hole, this leaves the screw almost flush with the top (outside) of the bore. I plugged the switch hole with a 3/8"x 1/2"nf screw and copper washer. Screw the large threaded plug back in and it is ready to go----it has worked good for me with no more hassles or leaks. For ORIGINALITY you can use the electrical switch on the top instead of a 3/8 plug but you will have to snip off its small brass plunger or it will activate the warning light and then you can still plug the wire in. --- USE THIS MODIFICATION AT YOUR OWN RISK.---
 
Yeah, at your own risk. What you have done is covered up the fact that your PDWA is defective (NOT the switch); and effectively converted your car back to single-circuit brakes.

I've already lost one TR because a hard line rotted through from the inside, draining all the brake fluid out. So I think I'll go the extra mile and actually fix my PDWA instead of covering up the problem.

There's even someone selling replacement PDWA pistons & seals on eBay for not very much.
 
If you didn't replace the plunger, then both the front & rear circuits share the bore. So as Randall stated, the benefits of a dual circuit (previously isolated by the seals on the plunger)are nil.

To eliminate the PDWA and still retain the dual circuit m/c, you could run a new line from the m/c to the 3-way fitting on the frame for the front, and run a new line from the m/c to the rear splitter. For the rear, it's easy to mount a 3-way splitter between the m/c and rear line, then plug the third hole with a bleeder. Or even use the pdwa as the rear splitter.
 
YEAH,--I have not covered anything up just eliminated an aggravation, The set screw isolates the two circuits just fine--by the tight fitting threads and it bottoming out on the shoulder--it effectively has two circuits and works. The PDWA was put on the USA models many british cars do not have a PDWA. My lines are in good shape with no problems, like I said "it is not for everybody" (purist and skeptics), but it does work and with two circuits.
 
Isn't it true that even if the plunger is off to one side it does not affect braking?(Assuming you have corrected whatever caused it to move). I guess there are other threads that have addressed this but I'm not sure on the outcome.

With that said, what is the true benefit of the PDWA considering that you sure don't need a light to tell you when the front brakes have failed?
 
Telly, the benefit of the PDWA is it will warn you if one circuit has failed and supposedly blocks off that failed circuit-- if it is actually working when that happens. It was put on the U.S. models to satisfy the Feds, many british cars do not have PDWAs. I feel my plug eliminates the PDWA and provides a two circuit system that many cars have without the PDWA.
 
ALLAN said:
YEAH,--I have not covered anything up just eliminated an aggravation, The set screw isolates the two circuits just fine--by the tight fitting threads and it bottoming out on the shoulder--it effectively has two circuits and works. The PDWA was put on the USA models many british cars do not have a PDWA. My lines are in good shape with no problems, like I said "it is not for everybody" (purist and critics), but it does work and with two circuits.
Click to expand...

I guess I missed that the set screw seals the two halfs of the bore. But to totally seal, I would expect more than just threads required, maybe some sort of thread sealer. Dunno. Mine uses 3-ways so it is isolated.
 
Peter, I do like your way of isolating the two circuits that you stated above and is a good option , I just feel my way makes it a little easier buy using the PDWA with the set screw, (just turns the PDWA into a junction block). Im confident that with the threads and seating on the shoulder there are two circuits with my set up.-------I only printed the "use at your own risk" statement because I have no Idea the capabilities, use of, or system condition of others using this mod., but It is a good alternative.
 
Telly said:
With that said, what is the true benefit of the PDWA considering that you sure don't need a light to tell you when the front brakes have failed?
Click to expand...
Sure seems like some folks need a light for the rear brakes, tho. Apparently two previous owners of the Stag I bought last year didn't realize that the rear brakes didn't work. One of them is a friend of mine, so I'm reasonably confident he isn't lying about it ... even though I discovered there was a problem within 100 miles of picking up the car.
 
The Brake lights work just fine on my TR6 without the PDWA hooked up. Do the PDWA switch and the brake pedal switch both have to be hooked up on the Stag for the brake lights to work??-------If your PDWA switch stoped working or the wire was riped off or accidentlly disconnected and then the brake lights didnt work because of it, what kind of saftey feature would that be??
 
No, the brake lights on the rear of the car are completely independant of the brake warning light on the dash; both Stag and TR6.

However, the warning light/PDWA should light if either the front or rear brakes lose pressure. And it won't work if the PDWA is disconnected.

BTW, the PDWA does not actually block off the failed hydraulic circuit. All it does is close the electrical circuit to the warning light on the dash. This is for all the people who disconnect the PDWA instead of re-centering the piston.
 
ALLAN said:
Telly, the benefit of the PDWA is it will warn you if one circuit has failed and supposedly blocks off that failed circuit-- if it is actually working when that happens....
Click to expand...
No, no, no! It does NOT block anything off! One more time, PDWA stands for Pressure Differential WARNING Actuator. Warning is all it does, via the light on the dash!
 
Andrew Mace said:
ALLAN said:
Telly, the benefit of the PDWA is it will warn you if one circuit has failed and supposedly blocks off that failed circuit-- if it is actually working when that happens....
Click to expand...
No, no, no! It does NOT block anything off! One more time, PDWA stands for Pressure Differential WARNING Actuator. Warning is all it does, via the light on the dash!
Click to expand...

Well it does not "block off" the failed circuit, but the plunger, if sealing properly, will allow the "good" circuit to maintain pressure. If you are going to ditch the PDWA, then better to just keep the brake circuits seperate altogether(from the M/C on), and not have the PDWA in there at all.

Rob.
 
I started a thread a couple of weeks ago on the PDWA. Mine was leaking/seeping out of the switch, and is now blocked off with a teflon tape wrapped bolt in the switch hole. I will look more into rebuild kits etc when time permits.

I had a front brake line blow once. The fuel filter was running against it and chafed through the line. It failed when I did a test emergency stop. Good to remember to do these once in a while.... the red light ain't going to help you if you blow a line when you need to stand on the brakes for real!
 
TR3driver said:
Telly said:
With that said, what is the true benefit of the PDWA considering that you sure don't need a light to tell you when the front brakes have failed?
Click to expand...
Sure seems like some folks need a light for the rear brakes, tho.
Click to expand...

That is a very good point about the rear brakes. The fronts do so much of the work you may not know when the rears have failed. So the PDWA is useful after all! /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
TR3driver said:
There's even someone selling replacement PDWA pistons & seals on eBay for not very much.
Click to expand...

I did a search for PDWA in current & completed ebay auctions & got 0 matches. How are they listed?
 
My apologies to all, it appears I overstated the eBay case. Oops !

It's been in my search results as a "new" listing every day for months now, but it appears it was really only one item, and it finally sold (or was removed for lack of interest). Plus, I didn't realize before, it's only for an early Stag.
https://item.express.ebay.com/Triumph-Sta...QQtabnavZ1#tabs
 
RobT said:
Well it does not "block off" the failed circuit, but the plunger, if sealing properly, will allow the "good" circuit to maintain pressure. If you are going to ditch the PDWA, then better to just keep the brake circuits seperate altogether(from the M/C on), and not have the PDWA in there at all.
Rob.
Click to expand...

Correct; if it did not seal the two circuits from each other, it couldn't work to detect a pressure differential. More importantly, it also prevents fluid from leaking out the bad side.
 
Back
Top