[AJD] What are failed Master Brake Cylinder Symptoms?

[Hans Krueger]

Dean VP wrote:

>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
>
>http://members.cox.net/classicweb/email.htm
>
>
>
>
>
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>
>  
>
see if you can find a power bleeder
then you can see if you got a rubber line that's expanding
on you
p.s.
don't let  that truck get the best of you
been their done that

-- 
Hans
hanskrueger at adelphia.net