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#Post#: 97538--------------------------------------------------
Series Three brake pressure differential warning switch thingy
By: ferretjuggler Date: May 17, 2015, 2:58 pm
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Looking through my hoard of series three spares today.
I'm bound to have another series three at some point, and that
is my excuse for not selling them on.
Anyway I found one of those pressure switch things wot tell you
if one of the dual brake circuits is loosing pressure.
It's in a really rough looking state.
Can I get a seal kit for it like you can for master cylinders
and wheel cylinders ???
Or is it non-repairable ???
#Post#: 97616--------------------------------------------------
Re: Series Three brake pressure differential warning switch thin
gy
By: jessejazza Date: May 22, 2015, 5:15 pm
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[quote author=ferretjuggler link=topic=9261.msg97538#msg97538
date=1431892729]
Looking through my hoard of series three spares today.
I'm bound to have another series three at some point, and that
is my excuse for not selling them on.
Anyway I found one of those pressure switch things wot tell you
if one of the dual brake circuits is loosing pressure.
It's in a really rough looking state.
Can I get a seal kit for it like you can for master cylinders
and wheel cylinders ???
Or is it non-repairable ???
[/quote]
I don't think they are really worth having on... tbh. The one's
been removed from mine and replaced with a single circuit
without servo.
#Post#: 97662--------------------------------------------------
Re: Series Three brake pressure differential warning switch thin
gy
By: NoelC Date: May 25, 2015, 4:56 pm
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Buggered if I can remember which one but either LRM or CLR had a
recent article about rebuilding the PDWA valve. I think they had
to source the parts based on measurements of the seals as there
wasn't a kit.
<edit>
HTML http://siteground237.com/~gunsandr/showthread.php?t=1379
HTML http://siteground237.com/~gunsandr/showthread.php?t=1379
- a
chap has done it here.
#Post#: 97665--------------------------------------------------
Re: Series Three brake pressure differential warning switch thin
gy
By: ferretjuggler Date: May 26, 2015, 1:59 am
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Thanks for that.
Very useful indeed.
Looks easy enough to rebuild.
I'm going to strip mine down when I have some spare time.
If it's full of corrosion it can go in the bin.
Otherwise I'll put it away somewhere nice and dry.
I might buy a late series three one day
#Post#: 97684--------------------------------------------------
Re: Series Three brake pressure differential warning switch thin
gy
By: ferretjuggler Date: May 26, 2015, 5:58 pm
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Stripped the thing down today without any issues.
Came as a bit of a surprise TBH because I'll come clean and
admit that I actually DUG THE THING UP whilst digging my back
garden :eek:
IIRC it came off a 1984 SWB diesel that I broke up around 2006.
A tiny little bit of corrosion at one end of the piston thingy
but nothing to worry about.
With reference to the possibility of the seals failing and
allowing your dual circuit brake system to effectively become
single circuit,
I had the idea of drilling the casting in the "dry" area where
the switch unit is located.
Then if either of the "O" rings failed, brake fluid would
simply piss out onto the chassis rail.
Fluid level in the reservoir would drop - low fluid level
warning switch activated - problem revealed.
OK so it's a bit overkill on an old leafer, just me
hyphothosising (fuck me that's a big word for me, especially as
I've just got back from the pub)
#Post#: 97705--------------------------------------------------
Re: Series Three brake pressure differential warning switch thin
gy
By: DarrenH Date: May 28, 2015, 4:07 am
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now that you have one apart, is it disassembled enough to see
how it actually works? seems to be some disparity between
anecdotal evidence, and printed evidence, as to wether it
actually "shuts off" brake fluid to the failed circuit, or just
flips the warning light by the ball+detent spring
#Post#: 97743--------------------------------------------------
Re: Series Three brake pressure differential warning switch thin
gy
By: ferretjuggler Date: May 30, 2015, 6:15 pm
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I can't see how it can "shut off" anything TBH
Yes I can see that it would be possible to build such a device
with the addition of a few more seals but this is just a warning
switch
#Post#: 97763--------------------------------------------------
Re: Series Three brake pressure differential warning switch thin
gy
By: DarrenH Date: May 31, 2015, 12:30 pm
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haynes manual plus other sources claim it has a shuttle valve
which flies up one end in the event of pressure loss, blocks
that circuit (hydraulically) while leaving the opposite end of
the vehicle leak free and working, plus of course puts the brake
fail light on the middle dash extension
#Post#: 97879--------------------------------------------------
Re: Series Three brake pressure differential warning switch thin
gy
By: ferretjuggler Date: June 8, 2015, 1:43 am
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A Haynes manual is a very dangerous thing if you are stupid
enough to believe anything written in there :wanker:
There's an easy way to put this to the test.
Back off a pipe union and see if the thing does indeed shut off
the fluid flow.
Or if you like drama, get someone to stamp on the pedal while
you take an axe to the brake pipes :giddy:
#Post#: 97880--------------------------------------------------
Re: Series Three brake pressure differential warning switch thin
gy
By: NoelC Date: June 8, 2015, 4:20 am
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The bleeding instructions for PDWA equipped series brakes do say
don't stamp on the pedal or the flow can be shut off to the
circuit so I presume the theory at least is it does shut off the
flow.
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