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Brake pedal keeps traveling - no fluid loss - Master cyl.?

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Brake pedal keeps traveling - no fluid loss - Master cyl.?

Postby Hondekop » Mon Jun 04, 2018 10:21 am

Morning Guys,

Since some time I can recognise a disturbing behaviour of my brake pedal. When I press it, it keeps traveling down, both with the engine off as well as running (it travels faster with the engine running, of course).
The strange thing is, I have driven at least 300 km like this and there is no fluid loss at all in the reservoir. Could it be a leaking master cylinder? But if so, where does the brake fluid go considering the fluid level in the reservoir does not change?
Here you can see an exploded view of the master cylinder. Car is MK4 1992 reg, non-ABS:
http://www.catcar.info/ford/?lang=en&l=bWFya2V0PT1ldXJvfHxjYXRfaWQ9PTQyNXx8Y2FiYnI9PURZfHx0aGs9PTB8fHN0PT02MHx8c3RzPT17IjIwIjoiRXVyb3BlIiwiMzAiOiJUcmFuc2l0IERZIDE5OTEtMTk5NCIsIjQwIjoiRSBCcmFrZXMgLSBCcmFrZSBQaXBlcyAtIFdoZWVscyIsIjUwIjoiRTAyIEJyYWtlcyAtIEJyYWtlIFBpcGVzIC0gV2hlZWxzLk1hc3RlciBDeWxpbmRlciBBbmQgQnJha2UgQm9vc3RlciIsIjYwIjoiRTAyMDEwIE1hc3RlciBDeWxpbmRlciAmIEJyYWtlIEJvb3N0ZXIifXx8YWxwaGE9PUV8fGdyb3VwPT1FMDJ8fHNlY3Q9PUUwMjAxMHx8c2V0PT1EWUUwMnx8aW1nPT1aMDAxMjMxNTAwfHxmMTI9PTEwNTE3OTIwKzA%3D

Cheers, Kai
1992 MK4 LWB van, 2.5 TD 101 HP
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Re: Brake pedal keeps traveling - no fluid loss - Master cyl

Postby Islander71 » Mon Jun 04, 2018 1:27 pm

Brake fluid will be getting past worn piston seals, but staying within unit. You need an overhaul kit or a new master cylinder. Better do it now....
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Re: Brake pedal keeps traveling - no fluid loss - Master cyl

Postby Hondekop » Tue Jun 05, 2018 8:51 am

Cheers. Ordered an overhaul kit. See if it cures the issue.
1992 MK4 LWB van, 2.5 TD 101 HP
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Re: Brake pedal keeps traveling - no fluid loss - Master cyl

Postby cherniy_chack » Tue Jun 05, 2018 2:21 pm

Islander71 wrote: You need an overhaul kit or a new master cylinder.

NO!NO!NO!
Only the replacement of the master cylinder with a new one!
Replacing the master cylinder seals-wasted time and money!
Believe the old mechanic.
I even changed the brake cylinders in the worst of times after a couple of unsuccessful repairs.
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Re: Brake pedal keeps traveling - no fluid loss - Master cyl

Postby Hondekop » Tue Jun 05, 2018 3:26 pm

cherniy_chack wrote:Replacing the master cylinder seals-wasted time and money!


Hm, I have replaced seals on brake calipers several times with good results, why would it be different in case of the master cylinder??
1992 MK4 LWB van, 2.5 TD 101 HP
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Re: Brake pedal keeps traveling - no fluid loss - Master cyl

Postby gotgcoalman » Tue Jun 05, 2018 11:05 pm

Hondekop wrote:
cherniy_chack wrote:Replacing the master cylinder seals-wasted time and money!


Hm, I have replaced seals on brake calipers several times with good results, why would it be different in case of the master cylinder??


corosion builds up (brake fluid is hydroscopic)

Even the tinyest imperfection will cause a new seal to fail sooner or later.(usually going downhill fully loaded) :(
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Re: Brake pedal keeps traveling - no fluid loss - Master cyl

Postby dumper » Wed Jun 06, 2018 2:08 pm

Over my working life I have resealed loads of master cylinders as instructed by my employer and never had a problem but if I did private work for mates or myself it was allways new quality parts you can’t put a price on safety at work if I resealed brake parts on job sheet I allways put resealed by instructions of management and if any parts looked suspect refused to do it
MK 8 L4 H3 Motorsport campervan
Past camper vans
1974 mk1 v4 with 2.0 pinto fitted
1986 mk3 2.5 di swb
1990 190 lwb 2.5 di
1998 100 lwb 2.5 di
2006 350 jumbo 135 tdci
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Re: Brake pedal keeps traveling - no fluid loss - Master cyl

Postby cherniy_chack » Wed Jun 06, 2018 5:15 pm

Hondekop wrote:Hm, I have replaced seals on brake calipers several times with good results, why would it be different in case of the master cylinder??

The operating conditions of the brake cylinders on the calipers differ from the working conditions of the sealing cups in the master cylinder.
In the master cylinder, the path traveled by the sealing cuffs is several times larger than the path traveled by the sealing cuffs in the rear brake cylinders.
And in the front brake cylinders, the cuffs do not move at all.
The pistons of the front brake cylinders are moved a very small distance, and the rubber sealing rings only deform when braking and return the original shape when braking stops.
If the master cylinder fails, there is a real threat to the safety of the driver's life and those around him, if any working (wheel) brake cylinder fails, much less.
No need to save on safety match.
Accident due to failure of brakes will lead to severe consequences and losses.
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Re: Brake pedal keeps traveling - no fluid loss - Master cyl

Postby Hondekop » Mon Jun 11, 2018 3:55 pm

OK, as the refurbishing kit had arrived yet, I decided to take the master apart. Keeping your thoughts in mind, I inspected the bore with an endoscope, no visible signs of rust or scratches, and then honed the bore. Built it back together and mounted it. Brake pedal is hard, no issues during test drive. I will keep an eye on it during the first thousand miles.

Ciao, Kai
1992 MK4 LWB van, 2.5 TD 101 HP
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Re: Brake pedal keeps traveling - no fluid loss - Master cyl

Postby cherniy_chack » Tue Jun 12, 2018 5:10 pm

Hondekop wrote: Brake pedal is hard, no issues during test drive. I will keep an eye on it during the first thousand miles.

After a few failures, I do not repair the brake cylinders.
Let you be lucky!
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Re: Brake pedal keeps traveling - no fluid loss - Master cyl

Postby Hondekop » Thu Jun 14, 2018 11:46 am

cherniy_chack wrote:Let you be lucky!

At least that's the intention :D .
1992 MK4 LWB van, 2.5 TD 101 HP
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