Stuck piston in PDWA

[sujitroy]

I got a PDWA from a swap meet / car boot sale. It's spare and going by the prices of these new, I don't want to toss it out. Unfortunately, the piston is stuck solid. I tried using compressed air and then a grease gun. I thought I could drill a hole down the piston and put an easy out down it to extract it, but a new piston I see is about $50. Are there any other non destructive ways on getting this piston out. It's currently sitting in a jar of Evapor rust.

Sujit

[jbuckl]

I think you are trying the correct way to loosen it.
Pehaps warm it up & spray with Wd40 or similar.
Cannot see it being terribly stuck even if it’s rusted.
Electro pickle might help, but may also eat the brass.
After derusting & lubricating, I cannot see it resisting a few sharp taps onto wood.
As far as I’m aware… the body allows access to tap the piston out in any case.

edit:- I’m wrong, the bore is blind…

you need to soak & pickle, having removed the steel collar.

then rinse with methylated spirits. Then dry it at 50/60 deg. C.

Then soak in vegetable oil / brake fluid.

Then attempt to tap out against a wooden block.

Please say how that goes.

New seals must be epdm, to work with brake fluid… do not use nbr or hnbr o rings in the braking system.

our suppliers are seemingly ignorant of this requirement.

brake fluid need epdm; engine oil needs nbr; hnbr or viton.

Its a travesty that this info is not followed.

it’s also a safety critical piece of information…. That appears not to be understood.

[trunt]

Moss sell a repair kit with piston, it’s used in many other cars of the period, eg MGB so you may find a used one somewhere

https://mossmotors.com/repair-kit-orig-assembly-with-lip-type-seals?assoc=176235

[DMT]

Have you tried to lever it out down the switch hole?

I used a scriber and it got it moving.

Dave

[sujitroy]

I have tried a few things thru the hole. no luck. I was thinking about getting my plumping torch on it to melt the Orings but that goo may glue it in.

[sujitroy]

Terry. Not much cheaper. This is a second spare. my first spare is apart.

[DMT]

Sujit

When you look down the switch hole can you see the piston centre groove? i.e. is it roughly central. If it is then if you fit a grease gun to the end hole then grease pressure must surely make it move in. Would this not release the stiction,.

If some of the central groove is showing, then a grease gun on the switch hole would create a pressure offset away from the blind end to push the piston outwards, I was never good ay physics.

[dasadrew]

Not much help if you don't have one, but an ultrasonic cleaning bath often works wonders in such cases, even if it takes a day or so of repeated bursts.

[sujitroy]

Sujit

When you look down the switch hole can you see the piston centre groove? i.e. is it roughly central. If it is then if you fit a grease gun to the end hole then grease pressure must surely make it move in. Would this not release the stiction,.

If some of the central groove is showing, then a grease gun on the switch hole would create a pressure offset away from the blind end to push the piston outwards, I was never good ay physics.

The piston is off center, but I can't move it with a scribe. I'll seal up my grease gun with PTFE tape and see if I can get it to move. Grease was oozing here and there. I'm using an old flexible brake line between my gun and the PWDA.
Sujit

[richardthestag]

From my experiences of Land Rover PDWA devices fitted to 1970s series 3 cars when they get that stuck then it is down to moisture in the brake fluid that has caused them to rust together.

Even if you do get it apart there will be a fair chance that it will leak fluid to the centre switch hole.

Early Range Rovers used the same PDWA as the Stag and I do have a few spares.

For your one I would stop picking and probing at it. load it with penetrating fluid or submerse it in diesel for a few days. If it isn't going to shift then it will ultimately be better off as a fishing weight

[sujitroy]

From my experiences of Land Rover PDWA devices fitted to 1970s series 3 cars when they get that stuck then it is down to moisture in the brake fluid that has caused them to rust together.

Even if you do get it apart there will be a fair chance that it will leak fluid to the centre switch hole.

Early Range Rovers used the same PDWA as the Stag and I do have a few spares.

For your one I would stop picking and probing at it. load it with penetrating fluid or submerse it in diesel for a few days. If it isn't going to shift then it will ultimately be better off as a fishing weight

I had another go at it yesterday. It is really stuck. It's going at the bottom of my pile of other non reusable Stag stuff. I agree with you Richard, even if I was able to get it out, it will most likely leak.
Sujit