Message text written by "R. Ashford Little II"
>I've heard. I've spoken with Dave @ TRF and Apple Hydraulics and they
>told me the following.
>
>1. Apple: the brake master draws 90% of it's fluid from the rear
>portion of the reservoir (front brake area) so it's not unusual that I'm
>not depleting the front reservoir area even by bleeding the rear brakes.
>
>TRF: didn't mention this and he thought that I since the front and back
>brakes are totally separate then this should not be the case.
The rear reservoir is larger because it services the front brakes and disk
brakes are self adjusting through the mechanism of advancing the pistons as
the pads wear. This requires a significant amount of fluid and a larger
reservoir is required to accomodate this. The baffle between the two
reservoirs does not extend all the way to the top of the plastic reservoir
and fluid level will equalize intil this level is achieved. Beyond that
they are separate.
>2. Both companies mentioned the PDWA as a likely culprit. Not that it
>was bad, but that the mere bleeding of brakes can cause the piston in
>the PDWA to go off center. If so then this is a possible reason for not
>drawing fluid from the front portion of the reservoir.
There is no hydraulid interconnection in the PDWA. Furthermore the PDWA
does not "shut off" flow to one side or the other. It merely signals an
imbalance in pressures front to rear which would result from a slow leak.
Even if it did shut off flow to one side that would not prevent fluid from
bleeding from the connection at the master cylinder. This is not the
issue.
>Question: I noticed that the wire that is supposed to be running from
>the PDWA switch to my dashboard is not hooked up. I see no wire that is
>left unconnected. Is this wire part of the wiring harness or is it a
>single wire that I could order and hook up?
Forensically speaking, this suggests that there has been a problem with the
brakes for a while and someone disconnected this wire to extinguish the
light. This is, of course, merely speculation.
However, if the fluid level is below the baffle and opining the front
connection causes a drop in the rear reservoir, then I suspect that the
port that leads from the front reservoir to the front portion of the bore
is blocked and fluid is passing past the fluid cup on the front piston.
The blockage may be a foriegn object (dirt?) or it may be that the return
spring is broken and the small fluid cup that closes off this port is not
pulling off the port.
In either event, I recommend dismantling the master cylinder and
finding/rectifying the problem.
Dave Massey
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