Subject: [TR] TR6 brake problem

From: Creig Houghtaling <[email-masked]>
Date: Sun, 26 May 2013 18:36:01 -0500

I'm trying to help my friend with his TR6 brakes and I've managed to make
things worse.  After working on his brakes, I now have no front brakes.  New
brake booster.  Rebuilt his master cylinder.  Rebuilt both front calipers.
New rear wheel cylinders.  New flex lines all 4 wheels.  We bled the front
and the back, so there was fluid moving in the lines then.  Went to drive
the car and only back brakes.  No front.  Pulled one front wheel and pried
the pads away from the disk.  The pistons on both sides moved easily, so I
think the calipers are OK.  Stepped on the brake pedal to reset the pads on
the disk.  Looked at the pads and there was still air between the pads and
disk.  It appears there is no fluid flowing to either front wheel.

Did I do something wrong on the MC rebuild that would allow it to work OK
for a time and then fail?  One friend suggested that the PDWA could be
stopping the flow.  Maybe some crud lodged somewhere?

I guess what I should do is have my friend hold the brake, then loosen pipe
fittings to see if they bleed.  If I disconnect the pipe from the MC and no
fluid comes out, that means my MC rebuild failed.

Has anybody else had anything similar to this?

** [email-masked] **

Archive: http://www.team.net/archive

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From: "Randall" <[email-masked]>
Date: Mon, 27 May 2013 12:13:54 -0700

> pdwa could well be the culprit!   I have fought them on several cars

That shouldn't be possible (which is not the same as impossible).  The PDWA
is not supposed to ever shut off the flow of fluid, only operate the big red
light on the dash.  The ends of the piston are tapered, so fluid can flow
around them even with the piston against one of the stops.

Randall

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From: triumph74tr6 <[email-masked]>
Date: Mon, 27 May 2013 19:24:27 -0500

It sure will if you get overzealous when bleeding. B That is exactly what it does.....closes off a perceived bad circuit. B 

Chad in TulsaRandall <[email-masked]> wrote:> pdwa could well be the culprit!B B  I have fought them on several cars

That shouldn't be possible (which is not the same as impossible).B  The PDWA
is not supposed to ever shut off the flow of fluid, only operate the big red
light on the dash.B  The ends of the piston are tapered, so fluid can flow
around them even with the piston against one of the stops.

Randall

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From: "Randall" <[email-masked]>
Date: Mon, 27 May 2013 19:58:35 -0700

PDWA = Pressure Differential Warning Actuator.  What it does is actuate the
warning (big red light on dash) when there is a pressure differential.  It's
not a valve at all, does not control flow at all.  The seals are only to
keep fluid from leaking out through the switch.

Take a look at http://goo.gl/fYlAz
You can see how both ends are turned down, so fluid can flow freely past
even when the piston is against the side of the housing.

-- Randall

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From: [email-masked]
Date: Tue, 28 May 2013 07:58:15 -0400 (EDT)

And if the O-ring did pass the opening that would create a path from the 
fluid circuits to the switch (which will not seal against the pressure -  or 
at all).

PDWA is an acronym for Pressure Differential Warning Actuator.  If it did 
more than just light the light the acronym would be different.

Great links.

Dave

In a message dated 5/27/2013 7:56:06 PM Central Daylight Time, 
[email-masked] writes: 
> See http://www.vtr.org/maintain/pdwa.shtml - the piston is a constant 
> diameter.  How would it shut off flow, without some careful positioning 
> of the o-ring, which shouldn't easily seal a round hole in the side of 
> the bore anyway.