[AT] RE: What are failed Master Brake Cylinder Symptoms?

[Dean VP]

Andy:

I haven't been able to get back to diagnosing this problem since last
Thursday. Hopefully will get to it again soon. And I don't yet know yet if
I'm really losing fluid during the brake pedal drain down. I lost quite a
bit of fluid bleeding the lines, etc and haven't had time to establish a
baseline of a full MC to determine if I'm pumping fluid somewhere. 

My first step will be to plug the new MC to see if it is the culprit or if I
have a failure in the Vacuum Assist unit or elsewhere. The Vacuum Assist is
under the floor and strangely there are two of them. It appears one has been
jury rigged in a location that is non-standard and another that looks
somewhat factory issue. However, the line connections lead me to believe the
factory location unit is the operative unit not the add-on. What is strange
is it appears from a preliminary inspection that both were in operation at
one time. The hoses and pipes appear to go to both simultaneously but the
outlet of one is disconnected.  I haven't figured out if it was a redundant
system at one time or what the heck the plumbing really did or does. 

If I can narrow the problem down to the Vacuum Assist area, then I will have
to try to figure out the plumbing jigsaw puzzle. 

The brake pedal does go all the way down w/o resistance until it is pumped
up repeatedly. But then does fade under pressure. However, it does return to
the neutral position by itself. What has me a bit baffled at the moment is
the new MC didn't change things much at all. Either I have a defective new
MC or problems elsewhere. The intended test with a plugged outlet on the new
MC will isolate that component. 

The wheel cylinders and the mechanical linkages, and adjusters were all
redone on this truck a couple of years ago. But as far as I know the MC and
the Vacuum Assist were not refurbished or replaced. 

My present guess is it is related to the Vacuum Assist unit somehow. All I
need is some available time right now to do more diagnostic work.

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



-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com] On Behalf Of Andy Glines
Sent: Tuesday, July 19, 2005 5:47 AM
To: at at lists.antique-tractor.com
Subject: [AT] RE: What are failed Master Brake Cylinder Symptoms?

Dean, you have gotten some good ideas from the list.  I Don't remember you 
telling us where the fluid went.  Did you find where it lealed out?  Is 
yours one with the booster mounted on the firewall of the truck or does it 
have the hydrovac unit under the floor?  Have you looked at the back side of

each wheel to look for leaks at the wheel cylinders?  When you refilled the 
MC and drove it how did it do?  I've had two MC fail on me the first one 
allowed the pedal to go to the floor with no brakes.  I could pull the pedal

back up with my foot and might have brakes on the next try.  Probably a bad 
check valve (1976 3/4 chevy).  On my 1973 Loadstar 1700 the pedal would 
travel down but not return.  I found that the rubber piece on the piston had

swollen and was sticking in the bore.  I suspect that someone put oil in the

MC instead of brake fluid.  I will rebuild the entire brake system on this 
truck before putting it on the road.
>----- Original Message -----
>From: "Dean VP" <deanvp at att.net>
>To: <at at lists.antique-tractor.com>; "AT JD"
><antique-johndeere at lists.antique-tractor.com>
>Sent: Wednesday, July 13, 2005 10:06 PM
>Subject: [AT] What are failed Master Brake Cylinder Symptoms?
>
>
> > I have a brake problem all of a sudden on 68 Ford N600. Brake pedal took
> > several pumps to develop pressure, then bleeds off under pressure. If 
>not
> > used for e few minutes takes several pumps again to get pressure and 
>then
> > bleeds down slowly under peddle pressure.   No improvement over time.
>Can't
> > tell if all four wheels are getting brake activity but there isn't much
> > braking power at all even under heavy foot peddle pressure. Fluid level 
>ok
> > and not dropping. Something is terribly amiss but I don't know how to
> > isolate the problem?  Master Brake Cylinder? Vacuum assist leaking? All
>four
> > hub cylinders leaking? Leaking line? (No loss of fluid right now but
>Master
> > Cylinder went dry over the winter during non-use!) A bunch of air in the
> > lines?
> >
> > I don't recall having brakes fail this drastically before or not
>eventually
> > self bleed. I'm really confused. Where do I start to diagnose the 
>problem?
> > Can this just be a Master Cylinder failure or is it something else? Sure
>not
> > safe to drive this way.
> >
> > I'm reluctant to start throwing parts at the problem until I know for 
>sure
> > what is wrong. Not sure I've ever had this major of brake failure 
>before.
>I
> > need help.
> >
> > Dean A. Van Peursem
> > Snohomish, WA 98290


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