[AJD] What are failed Master Brake Cylinder Symptoms?

Thu Jul 14 04:22:24 PDT 2005

Dean: If you have had the wheel cylinders replaced, then the leak apparently 
would be the vacuum assist cylinder leaking into the vacuum chamber, which 
would be an invisible leak. Either the master cylinder or the cylinder on 
the vacuum assist needs replaced/ rebuilt. I would suspect the vacuum assist 
unit if there is no indication of fluid leakage around the master 
cylinder.You could check the master cylinder by unhooking the line and 
plugging the cylinder to see if it pumps up and holds pressure by its self. 
That would tell you what direction to go next.

Headed to the Two-Cylinder Expo!

Bruce Mahr

----- Original Message ----- 
From: "Dean VP" <deanvp at att.net>
To: "'Antique John Deere mailing list'" 
<antique-johndeere at lists.antique-tractor.com>
Sent: Thursday, July 14, 2005 1:21 AM
Subject: RE: [AJD] What are failed Master Brake Cylinder Symptoms?

> Bruce:
>
> Let me try to establish the sequence again.
>
> 1.) Truck sets unused and outside over winter. Very wet but not much
> freezing weather.
> 2.) Spring check - When pressing break pedal no pressure. Peddle to the
> floor.
> 3.) Try to remove filler cap on Master Cylinder - Top (hex head) breaks 
> off
> w/o getting cap off. Finally get cap off w some difficulty. MC fluid 
> cavity
> dry as a cork. Fill with HD brake fluid.
> 4.) Try pumping brake. No pressure. Pump and pump and pump, an 
> extraordinary
> # of times. Almost give up but eventually get some pressure. But bleeds 
> down
> with constant pressure. If not pressed for a few minutes needs to be 
> pumped
> several times to get pressure back and then still bleeds down. Feels like
> fluid being pumped out a leak somewhere but no visible leak and fluid 
> level
> in MC not going down. Am getting some splash back in the MC cavity since 
> no
> cap on at present.  Occasionally will give impression it will hold under
> pressure but then if left alone for awhile and then pumped up again it 
> will
> bleed down.
> 5.) Not spongy like an air bubble at all. When peddle pressed and bleeds
> down it actually feels like a fluid leak but not losing fluid and no fluid
> leaks visible. Doesn't feel like air in the lines. Feels just like when 
> one
> opens the brake lines when bleeding them.
> 6.) Not getting any real pressure to the wheel brakes. Very scary and
> dangerous.
>
> Does this help in isolating the problem more?
>
> I guess I will try replacing the MC in the morning. But my gut tells me
> there is something more wrong besides the MC. Maybe I'm fencing with
> windmills. I have had all the wheel brake cylinders replaced a couple of
> years ago and all brake parts and adjusters cleaned up and lubed in the
> wheel hubs. But the MC was not replaced that I am aware of. I recall, at 
> the
> time, finding that a bit unusual since all the wheel cylinders were
> replaced. Just don't trust this sucker right now at all.
>
> I don't recall ever having a MC fail before so maybe I'm experiencing a 
> new
> phenomenon. I've had one really serious incident with this truck before 
> due
> to the brakes and brake lines. This makes me really nervous. Damned scared
> in fact. I dodged a bullet one time, and don't think I'll get a second
> chance.
>
> How does a Master Cylinder lose fluid w/o showing any visible signs? Don't
> understand that at all. Ends up in Vacuum assist? Leaking wheel cylinder?
> Behind firewall? Really confused!
>
> 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: antique-johndeere-bounces at lists.antique-tractor.com
> [mailto:antique-johndeere-bounces at lists.antique-tractor.com] On Behalf Of
> Bruce Mahr
> Sent: Wednesday, July 13, 2005 8:53 PM
> To: Antique John Deere mailing list
> Subject: Re: [AJD] What are failed Master Brake Cylinder Symptoms?
>
> Dean: Were the brakes OK after filling the master cylinder with fluid? If
> they were then you need to rebuild or replace the master cylinder.
> If the problem showed up after filling the master cylinder, then you need 
> to
>
> bleed the entire system, because air in it is causing your problem.
> Air in the lines and bad seals in the master cylinder will both give you 
> the
>
> problem you have, so it depends on when it showed up which you should do
> first.
> Wheel cylinders can leak enough from setting to empty the master cylinder
> without any visible evidence at any of the wheels for quite a long time, 
> due
>
> to brake dust and dirt inside soaking up the fluid before it becomes 
> visible
>
> on the outside.
> Also the vacuum booster cylinder can leak into the vacuum chamber and will
> drain the master cylinder but not show up externally.
> Your problem is definitely air, but why depends on too many things. I 
> would
> try bleeding the system first.
> I deal with this on my customers farm trucks all the time because of 
> setting
>
> most of the year.
>
> Bruce Mahr
>
> ----- 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 9:06 PM
> Subject: [AJD] 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
>>
>> 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
>>
>>
>>
>>
>>
>>
>> _______________________________________________
>> Antique-johndeere mailing list
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>>
>
>
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