PDWA NRC 7871 O rings

Message

Bern B · #1 Post by **Bern B** » Sat Jul 04, 2020 6:02 pm

My PWDA valve has failed And leaking through the sending unit. Was able to cap the sender and still have brakes. I want to rebuild it but am wondering if anyone has rebuilt one and if they know what size O ring are used inside, I’ve found out that the size of 2 O-Rings are 110 but can’t seem to figure out what size the end plug cap washer/ring is. If someone can confirm the sizes it would help. Would like to have the right parts before I take it apart. I have a new sending unit so just need the right seals
Thanks for any help

landcrabmechanic · #2 Post by **landcrabmechanic** » Sat Jul 04, 2020 6:10 pm

If you get it apart, take rings out to wraison seals in port kells. They make o rings and have billions in stock.

They can help you out.

Bern B · #3 Post by **Bern B** » Sun Jul 05, 2020 8:19 am

Thanks will do, I do want the right ones that are compatible with brake fluid. Only want to do it once and be good for another 30 years.

Bern B · #4 Post by **Bern B** » Sun Jul 05, 2020 8:33 am

Is it Grizzly Supplies, 19269 96 Ave, Surrey

radio_05 · #5 Post by **radio_05** » Mon Sep 28, 2020 6:45 pm

Can you order the genuine LR orings in?

They shouldn't be that expensive. Some parts you can use jobber for. I wouldn't skimp here.

Bern B · #6 Post by **Bern B** » Mon Sep 28, 2020 8:12 pm

I have looked on the internet but have not found any specific listing for them,
But tomorrow I will call the dealer and see if they can bring some in ,I have found the EPDM 110 o ring but having a problem with finding the 016 o ring .
Thanks

red90 · #7 Post by **red90** » Wed Sep 30, 2020 6:30 am

Just make sure the o-rings are EPDM.

Bern B · #8 Post by **Bern B** » Wed Sep 30, 2020 8:24 am

Yes that’s what I said the 110 are EPDM o rings But having a issue with getting 016 EPDM o rings I ordered some at Ackland’s but then after 2 months waiting they are back ordered, other suppliers on the internet want min $50 plus $20 for shipping,that’s just crazy for a $8.00 package of 25 o rings.

ANDYD · #9 Post by **ANDYD** » Wed Sep 30, 2020 5:28 pm

Hi Bernie,

Are you sure you want to rebuild it? May be safer just getting a new unit from Jeremy? Don't like to take chances with brakes :blackeye:
BTW My 110 manual says the unit is not re-buildable and should be changed out if failed?

Maybe a good time to upgrade to disc's on the front and rear (if you haven't already).$$$$$$$$$$$

-Andy

radio_05 · #10 Post by **radio_05** » Thu Oct 01, 2020 8:08 am

I agree with Andy here. Price out a replacement OEM/Genuine PDWA valve and get that in. Buy these orings and rebuild that as a future spare or trade item.

red90 · #11 Post by **red90** » Thu Oct 01, 2020 8:27 am

radio_05 wrote: Thu Oct 01, 2020 8:08 am I agree with Andy here. Price out a replacement OEM/Genuine PDWA valve and get that in. Buy these orings and rebuild that as a future spare or trade item.

I could be wrong but from my research OEM/Genuine PDWAs are NLA. You can get aftermarket ones.

The reality is the device is really not required and is not very useful when working. Installing a level switch in the reservoir (as per the later trucks) makes a lot more sense for an alarm.

bsa_m21 · #12 Post by **bsa_m21** » Fri Oct 02, 2020 11:40 am

If you have disk front brakes and drum back brakes, I believe that you do need some kind of bias valving in the circuit, whether PDWA, PRV (Pressure Reducing Valve), or a manual bias valve. Otherwise the drums will lock up long before the disks. No?

red90 · #13 Post by **red90** » Fri Oct 02, 2020 12:56 pm

The PDWA is not a bias valve. It is just a switch to alert to a broken line.

If you have a bias valve it is located in the rear brake line on the chassis (called a G valve). I believe these were only used on 90s

Bern B · #14 Post by **Bern B** » Sat Oct 10, 2020 1:32 pm

No it’s a safety feature
If you lose either brake lines front or rear the switch will slide and cut off the broken circuit and you still have brakes
This is a good thing
It also lights the warning light when you have a failure.

Bern B · #15 Post by **Bern B** » Sat Oct 10, 2020 1:34 pm

Oh let me buy a crappy after market failure
Good idea

red90 · #16 Post by **red90** » Sat Oct 10, 2020 3:33 pm

Bern B wrote:No it’s a safety feature
If you lose either brake lines front or rear the switch will slide and cut off the broken circuit and you still have brakes
This is a good thing
It also lights the warning light when you have a failure.

That is incorrect. It does not cut off the line. It just turn on a light on the dash.

Bern B · #17 Post by **Bern B** » Sun Oct 11, 2020 11:49 pm

So when you lose a brake line as In getting a hole/leak either in the front or rear line ,what ever line loses pressure the piston Inside the PDWA valve slides to the leaking side stopping the flow of brake fluid to the leaking side, that way you can still stop in a emergency brake failure.
Sounds like a very useful safety feature when it’s set up correctly.

I think I would rather trust the R&D from a corporation like Land Rover that they know what they are doing and what they design, NOT the internets back yard home mechanics that think they have more knowledge than the highly paid safety engineers at Land Rover.

Quote from the internet
“Its purpose is to offer a fail-safe method of bringing a Land Rover fitted with dual-circuit brakes to a halt, should the braking system suffer rapid fluid loss and therefore operating pressure. ... The PDWA, or brake failure switch, as it's more commonly known, is a simple mechanism in need of sympathetic understanding.“

The Rover-Landers of BC

The Rover-Landers of BC