OK, I need some net.wisdom. Here's the background:
Recently the brakes on my TR-3A (a low mileage, original car) began
to show the following symtoms: The brake master cylinder's internal
"plunger" would not come back to the normal/un depressed position
after taking my foot off the brake. Suspecting dirt or some other
problem, I rebuilt the master cylinder and the same problem occurs.
Note: the plunger moves freely within the bore, and resets itself
with no problem if the brake line is not connected. I find,
however, that the problem seems to be that upon lifting my
foot off the brake pedal, the plunger is in a "vacuum" mode and
the plunger just stays where it was depressed to. I can duplicate
that by just holding my finger over the hole that the brake line
connects to. My understanding is that upon release, if such a vacuum
exists, then the brake master cylinder should be getting fluid from the
master cylinder reservoir. That does not seem to be the case, although
I can detect no obstruction in the reservoir to master cylinder connection.
I used girling rebuild kit GISP1995, and replaced all rubber parts
plus the little circular spring, so I don't suspect them being at
fault.
Possible explanation: the plastic spacer is worn and not providing
proper clearance to allow the master cylinder to draw in brake fluid
from the reservoir as it should?
There's a partial blockage in the reservoir to master cylinder line,
or in the master cylinder itself?
Any other thoughts, ideas would be appreciated. Anyone ever encounter
this same problem before?
Bottom line is that it is impossible, therefore, to bleed the brake
system, since there's no fluid coming in to the master cylinder EXCEPT
when the plunger is totally in the "at rest" position. I verified
that by just letting the cyclinder stand with a separate line connected
which vented to a container. Eventually, fluid just flowed from the
reservoir, through the master cylinder, and then out the "test line"
I had connected, so the reservoir doesn't appear to be at fault.
As the original master cylinder bore was clean, and there was no leaking,
I'd like to avoid buying a new master cylinder, so any thoughts would be
appreciated.
-----------------------------------------------------------------------
Bill Sohl (K2UNK) BELLCORE (Bell Communications Research, Inc.)
Morristown, NJ email via UUCP bcr!cc!whs70
201-829-2879 Weekdays email via Internet whs70@cc.bellcore.com
|