740 clutch hydraulic problem

  • Thread starter Thread starter James Sweet
  • Start date Start date
J

James Sweet

So I went to drive my '87 740T today which had been sitting for about a week
and I stepped on the clutch and felt no resistance. Looked under the hood
and the slave cylinder is fully extended holding the clutch disengaged,
fluid resivoir is a bit low as well. I have a second car but I need to fix
this ASAP, what should I look for? The car has 255k on it and has never had
a hydraulic problem that I'm aware of.
 
Because there's more to the internet than hits alone, James Sweet
wrote:
So I went to drive my '87 740T today which had been sitting for about a week
and I stepped on the clutch and felt no resistance. Looked under the hood
and the slave cylinder is fully extended holding the clutch disengaged,
fluid resivoir is a bit low as well. I have a second car but I need to fix
this ASAP, what should I look for? The car has 255k on it and has never had
a hydraulic problem that I'm aware of.
Click to expand...


I'd try loosening the bleed nipple to see if the system is
pressurised. If it is, then the fluid is not being allowed back into
the reservoir, so I'd suspect the master cylinder - piston not
returning properly.

The mystery is how the slave became extended while it just sat there.
It's a pretty powerful spring it pushes against. Did the clutch get
operated before you found there was no resistance?

In my experience, replacing the rubber seals in the master cylinder is
rarely worth while - get a complete new cylinder; they are not so much
more expensive than a seals kit, and the seals kit may not do the job
properly anyway.


--

Stewart Hargrave

I run on beans - laser beans


For email, replace 'SpamOnlyToHere' with my name
 
Stewart Hargrave said:
Because there's more to the internet than hits alone, James Sweet
wrote:



I'd try loosening the bleed nipple to see if the system is
pressurised. If it is, then the fluid is not being allowed back into
the reservoir, so I'd suspect the master cylinder - piston not
returning properly.

The mystery is how the slave became extended while it just sat there.
It's a pretty powerful spring it pushes against. Did the clutch get
operated before you found there was no resistance?

In my experience, replacing the rubber seals in the master cylinder is
rarely worth while - get a complete new cylinder; they are not so much
more expensive than a seals kit, and the seals kit may not do the job
properly anyway.
Click to expand...

Well I had a look at it tonight, seems the master cylinder is fine, what
happened is the slave cylinder got extended far enough that the rubber seal
on the piston got caught against the opening of the bore, how it got
extended that far I'm not really sure, but I reasembled it with the damaged
seal and verified proper clutch function. Ordered a new slave cylinder
tonight so hopefully installing that will fix it.
 
If your real lucky the slave shaft got hyper extended and bound being cylnder is
loose in it's hole,judisious thump? Shim the hole? or lengthen the rod?
 
Because there's more to the internet than hits alone, James Sweet
wrote:

Well I had a look at it tonight, seems the master cylinder is fine, what
happened is the slave cylinder got extended far enough that the rubber seal
on the piston got caught against the opening of the bore, how it got
extended that far I'm not really sure, but I reasembled it with the damaged
seal and verified proper clutch function. Ordered a new slave cylinder
tonight so hopefully installing that will fix it.
Click to expand...


It's strange that it works normally now. I was thinking it may
possibly indicate that some part of the clutch mechanism is worn
beyond it's sevice limit. Clutch plate wear should shorten the travel
of the slave, but if the thrust bearing or spring plate or actuating
arm are worn or damaged it could allow the slave to extend too far.


--

Stewart Hargrave

I run on beans - laser beans


For email, replace 'SpamOnlyToHere' with my name
 
Bill Chaplin said:
If your real lucky the slave shaft got hyper extended and bound being cylnder is
loose in it's hole,judisious thump? Shim the hole? or lengthen the rod?
Click to expand...

On mine I found the plastic end of the slave actuator had worn there it
locates into the hole in the clutch arm. My cheap solution was to fit an old
nut in the cup of the piston to make the rod longer. Lasted for years.

Stuart.
 
Stewart Hargrave said:
Because there's more to the internet than hits alone, James Sweet
wrote:




It's strange that it works normally now. I was thinking it may
possibly indicate that some part of the clutch mechanism is worn
beyond it's sevice limit. Clutch plate wear should shorten the travel
of the slave, but if the thrust bearing or spring plate or actuating
arm are worn or damaged it could allow the slave to extend too far.
Click to expand...

I should have mentioned the clutch assembly and thrust bearing were replaced
about 2k miles ago, the rod will extend further with a fresh clutch than a
worn one, still I find it odd that it did this. It must have happened when I
pressed the clutch to place it in gear after parking it.
 
Stuart Gray said:
a never

On mine I found the plastic end of the slave actuator had worn there it
locates into the hole in the clutch arm. My cheap solution was to fit an old
nut in the cup of the piston to make the rod longer. Lasted for years.

Stuart.
Click to expand...

I'll try that, I'm not sure what bits the new cylinder comes with.
 
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