PDWA Switch

[mopoole]

Having suffered loss of brake fluid from one of the circuits, the shuttle has deviated to one side. The ROM shows a diagram where access to both ends of the shuttle is possible via two nuts to enable it to be re-centralised. The PDWA switch on my car has only one nut at one end, the other end being part of the casting and obviously no nut. Would be grateful if anyone can suggest how to re-centralise the shuttle in this situation.

Many thanks

Maurice

[Rigid]

Alternatively (if you have plenty of brake fluid handy) open bleed nipples one at a time, pressing the pedal until the light goes out.
Note, the front brake fluid chamber feeds the front discs, the rear chamber feeds the rear drums.

It isn't foolproof but with care you can shuttle the shuttle into the centre by foot pressure and juggling alone.

Note - I've adopted this method becase I can't get any of the brake line nuts out of the PDWA body - rusted solid.
If I ever get the urge to spend money I would need new brake lines as well - things will get ruined with my go to disassembly techniques - ie. brute-force and ignorance.

[sujitroy]

It was difficult for me to see which way mine moved. I had to remove it from the car. remove the switch and you can get a small pointed Bradle in there to move it.

[DJT]

Centralising the PDWA is described in the ROM. 70.25.02 para 11.

[jbuckl]

There are lots and lots of posts about this. search ‘pdwa’

Some of them include warnings about working on brakes if you aren’t competent.

my take is if the switch isn’t leaking it’s still safe…. It doesn’t affect the system.

ensure there aren’t leaks elsewhere too.

if all else fails, take the valve off.

take the blanking plug out.

remove the piston.

replace seals.

refit the valve.

fit a holding bolt.

bleed the system.

fit the switch.

if all that is too much much faff, entrust that list to a.n. Other.

no offence intended.

[richardthestag]

Sorry but the rom is right and it is wrong, who would ever have believed that.

pdwa1.png

That is the circuit for reference.

And I assume that the brake issue has been resolved and the balance valve just needs resetting.

BTW this is the diagram from the ROm that I think is misleading
pdwa2.png

It doesn't look like that!

Where was the failure? if back end then

with ignition on to show the light or with a multimeter to the switch pin connected

connect a bleed tube to the front end, open the bleed screw and slowly press the pedal until the light goes out.

or vice versa

[richardthestag]

there are lots and lots of posts about this. Search ‘pdwa’

some of them include warnings about working on brakes if you aren’t competent.

amen

I might have to worry about the sanity of someone who might suggest otherwise

[sujitroy]

Having bled the brakes a few times on a classic Mini with one circuit. Always start from the furthest cylinder. I used the same principle on the Stag until that light bulb moment came on and you can bleed the front furthest first as they are on a different circuit

[gbb483]

I had a great deal of difficulty recentralising mine, however it had been wedged to one side for years (a PO had just disconnected the lead from the switch and ignored it). If yours has only just moved, it should be relatively free and the bleeding trick mentioned above should see you straight.

[mopoole]

Thanks all for your advice. Yes I'm fully aware of working on safety critical areas such as brakes having upgraded them with Chris Witor's vented discs and done the same on my previous TR5. The current switch is leaking and rather than attempt to centralise the shuttle and bugger up a part nla, am sourcing a NOS one from Tony White. Will keep you informed.

Maurice

[mopoole]

Well, an update.
Received the NOS PDWA switch from Tony which obvious needed a good clean and check to see if the shuttle was central which surprisingly it was.
Plan of action - disconnect all 5 pipes and cap with bleed nipple caps to stop the top 2 siphoning the brake fluid out of the master cylinder and the bottom 2 and F/N/S to stop ingress of muck.
Re-connected top & bottom pipes loosely before refitting the switch as thought be easier to line up the pipes and avoid any tensions in the pipes which would make threads "catching" more difficult. Unfortunately the pipe to F/N/S caliper has refused to catch. Cleaned the threads with the relevant tap/die and tried fitting that one first but to no avail; still won't catch

Am getting very frustrated so would be grateful of any ideas as to how to proceed before I do something drastic!!!!

Answers on a postcard please..............

Seriously, any suggestions as to how to get it to catch would be much appreciated

Thanks
Maurice

[FrenchStag]

Deep breaths. Dont hit it with anything.

Buy a new brake line with new fittings and try it before fitting.

Is it the part going into the caliper itself that wont catch? Or the connection to the pdwa?

I assume you are going in dead straight?

[gbb483]

As I recall, the F/N/S comes from the centre of the blanking plug. Swap it with your old one and see if it solves your problem.

[gbb483]

Things are further complicated by two different threads being used :

PDWA Rear in and out - 3/8 UNF
PDWA Front in and out - 7/16 UNF

[mopoole]

Well, finally did it. After much unscrewing and re-screwing all the pipes in various orders it finally caught. Managed to top up the new PDWA switch with brake fluid and now borrowing a friend's right leg, should be up and running tomorrow.
Thanks for everyone's help

Maurice