[AJD] What are failed Master Brake Cylinder Symptoms?

[Dean VP]

Now that I reread the earlier messages, I know understand better what you
were trying to tell me about plugging the MC to see if it operated properly.
I didn't have anything here then to plug the outlet of the MC so didn't
properly complete that test. Now that I have purchased a replacement MC, I
now have two threaded plastic plugs, one of which I used to bench bleed the
replacement, rebuilt MC. 

I didn't like the way the bench bleeding of the replacement MC went either.
The instructions that came with the replacement MC said to manually compress
the piston until it would only move about an 1/8". I never achieved that,
even after several pumping sessions. I suspect I got it to stop at slightly
less than 1/2".  I was troubled by that but it would hold pressure and stop
at that point. 

I'm reporting this in case this information might be significant.

Another thing that troubled me was I installed the MC on the firewall with
the temporary plastic plug still in, per instructions, then removed the
plastic plug and installed the brake line. Lost some fluid installing the
connection. I should have tried the brake pedal with the plastic plug still
installed but it didn't dawn on me to do so at the time. Dumb!

But after I connected the brake line to the MC I did start pumping the brake
pedal. No pressure at all. Pumped the pedal over and over, bled the line to
the Vacuum Assist, pumped the pedal some more and finally got some
resistance on the pedal. Almost identical results to when I first added
fluid to the old MC. These new results immediately told me I was still in
trouble. But I proceeded down the chain of hydraulic lines, bleeding as I
went and then bled each wheel valve twice. Got air on three of the 4 wheels.
But..... No improvement of the pedal drift down after initial resistance. No
real change after bleeding the lines at all, which surprised me a bit.
Actually the new MC wasn't performing noticeably better than the old one. A
big disappointment. 

When I get some free time, I'll next block the outlet of the new MC and see
if it holds there with the plug in. If it does, I'll just work my way down
the chain until I isolate a spot causing the pedal drift. Don't know how I
will plug some of the fittings yet but I'll have to get creative some how.
Not sure the plastic plugs will work on the smaller fittings. It is a male
plug and in some spots I need a female plug. 

One other curious piece of data is, I am unable to detect any difference
whether the truck is running or not. For some reason I expected a change due
to the vacuum assist. Now, I can't remember what the difference was when the
brakes were working properly. This also has me a bit baffled.

Why can't I have simple problems?

Part of the problem I have working on this thing is I really get nervous
crawling under this truck. It took me months to get over having this truck
run over me a couple years ago. I got so close to being killed by this truck
due to a broken line it caused me nightmares for a long time and 6 months of
very slow rehabilitation. I missed death by a whisker and I have never
forgotten it. Just have to get my mind to overcome that old fear. Needless
to say it is currently parked on a perfectly flat area with all kinds of
wheel chocks but it really is a challenge to crawl under this thing. I'm
probably never going to get over that near miss experience. And probably
shouldn't either. 

Have three busy, full schedule days ahead so probably won't get back to this
until Monday. Maybe a bolt of lightening will hit me and make all this
completely clear or no longer important!  :-) Or something I have included
in this message will trigger something from you folks that identifies where
the real problem is. I do appreciate all the input and suggestions I have
received. Thanks a bunch. I think I now have learned from all your
suggestions how to methodically work my way through the components to
isolate the problem. No different than most trouble shooting procedures. At
least now I understand the proper sequence.  I hate kaleidoscope replacement
of parts to find a problem. Made one mistake already on the MC. Hopefully it
is the last. 

Dean A. Van Peursem
Snohomish, WA 98290

I'm a walking storeroom of facts..... I've just lost the key to the
storeroom door 


www.deerelegacy.com

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