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BMW Clutch Issue



 
 
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  #11  
Old June 15th 07, 10:58 PM posted to rec.autos.tech,alt.autos.bmw
Nate Nagel[_2_]
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Posts: 4,686
Default BMW Clutch Issue

Scott Dorsey wrote:
> Bill > wrote:
>
>>Clutch system is not bled properly. If the hardware is there, and new, the
>>fluid is good, then it can ONLY be that the system is not bled, i.e. there
>>is air in the line.

>
>
> That would make perfect sense, and the fact that it is okay when cold but
> undrivable when hot correllates well with the air in the line diagnosis.
> BUT, the system has been bled many many times at this point. I cannot imagine
> there is still any air in it.


How is it being bled? I find that a pressure bleeder is the only way to
fly.

nate

--
replace "roosters" with "cox" to reply.
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  #12  
Old June 16th 07, 12:03 AM posted to rec.autos.tech,alt.autos.bmw
Bill[_4_]
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Posts: 169
Default BMW Clutch Issue


"Nate Nagel" > wrote in message
...
> Scott Dorsey wrote:
> > Bill > wrote:
> >
> >>Clutch system is not bled properly. If the hardware is there, and new,

the
> >>fluid is good, then it can ONLY be that the system is not bled, i.e.

there
> >>is air in the line.

> >
> >
> > That would make perfect sense, and the fact that it is okay when cold

but
> > undrivable when hot correllates well with the air in the line diagnosis.
> > BUT, the system has been bled many many times at this point. I cannot

imagine
> > there is still any air in it.

>
> How is it being bled? I find that a pressure bleeder is the only way to
> fly.
>
> nate

-----

Just a thought: you might try blleding it in reverse. Maybe pressurize the
fluid and send it into the system from the slave cylinder end. You'd have to
drain some fluid from the master cylinder reservoir first and keep an eye on
it. OR you could unbolt the slave and shake it while still attached to the
hose. Maybe there's just enough air to present a problem eventhough the
bleeding appears good. Either way, there's air in the system now.

Bill in Omaha
'86 535i


  #13  
Old June 16th 07, 12:07 AM posted to rec.autos.tech,alt.autos.bmw
Nate Nagel[_2_]
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Posts: 4,686
Default BMW Clutch Issue

Bill wrote:
> "Nate Nagel" > wrote in message
> ...
>
>>Scott Dorsey wrote:
>>
>>>Bill > wrote:
>>>
>>>
>>>>Clutch system is not bled properly. If the hardware is there, and new,

>
> the
>
>>>>fluid is good, then it can ONLY be that the system is not bled, i.e.

>
> there
>
>>>>is air in the line.
>>>
>>>
>>>That would make perfect sense, and the fact that it is okay when cold

>
> but
>
>>>undrivable when hot correllates well with the air in the line diagnosis.
>>>BUT, the system has been bled many many times at this point. I cannot

>
> imagine
>
>>>there is still any air in it.

>>
>>How is it being bled? I find that a pressure bleeder is the only way to
>>fly.
>>
>>nate

>
> -----
>
> Just a thought: you might try blleding it in reverse. Maybe pressurize the
> fluid and send it into the system from the slave cylinder end. You'd have to
> drain some fluid from the master cylinder reservoir first and keep an eye on
> it. OR you could unbolt the slave and shake it while still attached to the
> hose. Maybe there's just enough air to present a problem eventhough the
> bleeding appears good. Either way, there's air in the system now.
>
> Bill in Omaha
> '86 535i
>
>


I'd also tap on each cylinder while bleeding with a wrench or
screwdriver if it appears like it is possible for a bubble to form and
not get pushed out with the fluid flow. Make sure that the bleeder is
at the very top of each component, if it is not I second Bill's advice
to unbolt.

nate

(never had a problem with the clutch on my 535i... blew up the motor,
but didn't have a problem with the clutch.)

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel
  #14  
Old June 16th 07, 12:13 AM posted to rec.autos.tech,alt.autos.bmw
Steve B.
external usenet poster
 
Posts: 346
Default BMW Clutch Issue


>That would make perfect sense, and the fact that it is okay when cold but
>undrivable when hot correllates well with the air in the line diagnosis.
>BUT, the system has been bled many many times at this point. I cannot imagine
>there is still any air in it.
>

With rubber brake lines sometimes the inside fails in such a way that
when you step on the brake the fluid is forced to the caliper and
stops the car then when you let off the brake the broken piece in the
hose swings around and acts like a one way valve effectively locking
the brake in the on position.

I assume there must be a similar hose on the clutch system to allow
for movement of the transmission. Has this hose been replaced?

Steve B.
  #15  
Old June 16th 07, 01:00 PM posted to rec.autos.tech,alt.autos.bmw
jim
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Posts: 546
Default BMW Clutch Issue



Scott Dorsey wrote:

>
> It means the former.


OK so you push the pedal to the floor, at that point you find that the
transmission is not disengaged and when you lift your foot you find that
the pedal is not returning? Right?
I think the way it works on these is the hydraulic pressure from the
slave pushes the master and thus returns the pedal. You can assume that
the problem is not a line blockage or sticking clutch that prevents the
return of the fluid because if that were the case the transmission would
be stuck in disengaged not stuck in engaged. Anyway, If anything
mechanical was sticking or bent or broken it's difficult to see how
pulling on the pedal and/or pumping it could fix that, so it would seem
that the only explanation is hydraulic pressure is lost between the
slave and master cyl. I assume you would look for and notice an external
leak? I suppose it is possible that if the line was near the exhaust
boiling the brake fluid could be the cause.

>But all of the hydraulics have been replaced. I
> don't see anything else that can be replaced. I do not see any sort of
> check valve anywhere that could be leaking, either.


Yes there is a check valve. The piston inside the master cylinder
behaves as a check valve. This is why pumping restores the lost fluid
between slave and master. If that seal leaks while stepping on the
clutch then the fluid goes back into the reservoir and you get the
symptoms you describe. Assuming a faulty master cyl. is not the cause, I
suppose it's possible that the wear on the pedal linkage may be causing
a stress on the piston for which it was not designed. A side load or
excess travel causing the piston seal to fail.

-jim



>
> >> I could pull the pedal up and pump it down a couple
> >> times and the clutch would open properly again.

> >
> >What does "clutch would open properly" mean. If you don't do the pumping
> >thing then the transmission will remain engaged? or remain disengaged?
> >or what?

>
> It will remain engaged, with the pedal stuck to the floor, which is bad.
>
> >>It started happening now
> >> and then, and then more and more often.

> >
> >Has your mechanic actually been able to reproduce the problem or is he
> >going only by your description of the problem? If he has seen the car
> >when the problem exists I would take it to another mechanic.

>
> He has been able to reproduce it while driving but not up on the lift.
> I am annoyed that he has been trying to fix the problem by swapping things
> out, but by the same token everything has BEEN swapped out at this point.
> --scott
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."


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  #16  
Old June 16th 07, 05:14 PM posted to rec.autos.tech,alt.autos.bmw
Bill[_4_]
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Posts: 169
Default BMW Clutch Issue


> > >Has your mechanic actually been able to reproduce the problem or is he
> > >going only by your description of the problem? If he has seen the car
> > >when the problem exists I would take it to another mechanic.

> >
> > He has been able to reproduce it while driving but not up on the lift.
> > I am annoyed that he has been trying to fix the problem by swapping

things
> > out, but by the same token everything has BEEN swapped out at this

point.
> > --scott

-----
Does "swapped" mean "replaced with new or rebuilt", or just lip service by a
half-assed mechanic?

Top down:
Fluid reservoir
hose to
Clutch Master Cylinder (no bleeder valve)
hose to
Clutch Slave Cylinder (bleeder valve)

Other directly-related stuff:
Clutch pedal w/return spring and adjuster to CMC
Rod between slave cylinder and fork (part of the slave cylinder)
Clutch actual (fork, release bearing, disc, pressure plate)

Notes:
The return spring on the pedal is a helper.
The main back pressure comes from the clutch pressure plate spring fingers.
These guys give more than 220 pounds of resistance when disengaging the
clutch.
Given a completely hydraulic connection, the pedal would have no choice but
to return to full out position.

I'm a little surprised you haven't found a leak yet. Have you noticed a drop
in the fluid reservoir level? If the level is below the MIN line, the clutch
supply line will suck air. But it wouldn't affect the clutch operation until
the air got to the Clutch Master Cylinder (attached to the pedal). Pumping
the pedal creates a short-term fix by temporarily compressing the air enough
to slightly disengage the clutch disc. I know it's been said, but I'd
replace completely the items under Top Down. The reservoir should be OK,
though. If this keeps up, your clutch will die. It may even take the
transmission with it. Good Luck.

Bill in Omaha
'86 535i


  #17  
Old June 16th 07, 06:19 PM posted to rec.autos.tech,alt.autos.bmw
Dave Plowman (News)
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Posts: 1,533
Default BMW Clutch Issue

In article >,
Scott Dorsey > wrote:
> Starting around 220,000 miles, the clutch began sticking closed. That
> is, I'd put my foot down, the pedal would stick to the ground, and the
> clutch would remain engaged. I could pull the pedal up and pump it down
> a couple times and the clutch would open properly again. It started
> happening now and then, and then more and more often.


> I replaced the plunger on the clutch master cylinder, which was leaking,
> on the suspicion the seal in it was bad. Didn't fix anything. Took it
> to a respected BMW indy mechanic around here, who swore I did it wrong
> and replaced the plunger again. Didn't fix anything. Replaced the
> whole master cylinder. Didn't do anything. Changed the fluid and
> replaced the slave cylinder. Still no go.


If it pumps up it can only really be hydraulic related. If you've fitted a
new slave cylinder I'd guess the master cylinder needs replacing - not
just new seals. Also bleeding these can be difficult - best to use a
pressure bleeder, or unbolt the slave cylinder, clamp the piston, and
raise it above the master (if the pipe allows)

One other thought - does the pedal sink to the floor after time if the car
is just parked up and not started? If so it's got to be hydraulics. If it
is fine on this test it's just possible run out on the withdrawal bearing
or the clutch parts this bears on etc is upsetting the correct clearance -
but that's a long shot, and should be pretty obvious by looking.

--
*Arkansas State Motto: Don't Ask, Don't Tell, Don't Laugh.

Dave Plowman London SW
To e-mail, change noise into sound.
  #18  
Old June 16th 07, 07:59 PM posted to rec.autos.tech,alt.autos.bmw
Scott Dorsey
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Posts: 3,914
Default BMW Clutch Issue

Dave Plowman (News) > wrote:
>
>If it pumps up it can only really be hydraulic related. If you've fitted a
>new slave cylinder I'd guess the master cylinder needs replacing - not
>just new seals. Also bleeding these can be difficult - best to use a
>pressure bleeder, or unbolt the slave cylinder, clamp the piston, and
>raise it above the master (if the pipe allows)


Master cylinder has been replaced twice now. Pressure bleeder has been
used.

>One other thought - does the pedal sink to the floor after time if the car
>is just parked up and not started? If so it's got to be hydraulics. If it
>is fine on this test it's just possible run out on the withdrawal bearing
>or the clutch parts this bears on etc is upsetting the correct clearance -
>but that's a long shot, and should be pretty obvious by looking.


After replacing all the hydraulics my first thought was the bearing, so
we replaced that too. The shaft does not appear worn or have a lip on it.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #19  
Old June 16th 07, 10:29 PM posted to rec.autos.tech,alt.autos.bmw
Dave Plowman (News)
external usenet poster
 
Posts: 1,533
Default BMW Clutch Issue

In article >,
Scott Dorsey > wrote:
> Dave Plowman (News) > wrote:
> >
> >If it pumps up it can only really be hydraulic related. If you've
> >fitted a new slave cylinder I'd guess the master cylinder needs
> >replacing - not just new seals. Also bleeding these can be difficult -
> >best to use a pressure bleeder, or unbolt the slave cylinder, clamp the
> >piston, and raise it above the master (if the pipe allows)


> Master cylinder has been replaced twice now. Pressure bleeder has been
> used.


> >One other thought - does the pedal sink to the floor after time if the
> >car is just parked up and not started? If so it's got to be hydraulics.
> >If it is fine on this test it's just possible run out on the withdrawal
> >bearing or the clutch parts this bears on etc is upsetting the correct
> >clearance - but that's a long shot, and should be pretty obvious by
> >looking.


> After replacing all the hydraulics my first thought was the bearing, so
> we replaced that too. The shaft does not appear worn or have a lip on
> it. --scott


But does the pedal sink to the floor after the car has been standing
without the engine running? Also, how freely does it move when in this
state? An experienced mechanic should be able to 'feel' by hand if it's
moving the slave cylinder and withdrawal arm or just the master cylinder
piston.

This stationary test should tell all. If the hydraulics work consistently
with normal pedal feel after the car is parked up for some time and the
engine not started they must be ok. If the excessive 'slack' only happens
with the engine running something is pushing the slave cylinder piston too
far back. The bearing might well be ok but now about the parts on the
clutch it bears on? I'm not sure which type of clutch is fitted to your
model but if the type where the release bearing pushes direct on the
'fingers' of the diaphragm spring, are those all at the same height as it
were?

--
*To steal ideas from *one* person is plagiarism; from many, research*

Dave Plowman London SW
To e-mail, change noise into sound.
  #20  
Old June 27th 07, 10:00 PM posted to rec.autos.tech,alt.autos.bmw
E28 Guyİ
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Posts: 139
Default BMW Clutch Issue

On Jun 14, 8:56 pm, (Scott Dorsey) wrote:
>
> Help! Anybody have any suggestions about what could be causing this issue?


Having read everything else suggested and all you've tried, one last
thing occurs to me.

The E28 is subject to cracking pedal brackets. The stamped metal
assembly that holds your master cylinder and the clutch pedal cracks
from stress and wreaks all kinds of havoc because of it. It can
destroy a new master cylinder quite quickly, so check yours as you do
this job. You can either replace it with a new one (they aren't
expensive) or weld your old one up (with reinforcement in the obvious
area where it cracked). Good luck.
--
C.R. Krieger
Been there; haven't cracked mine yet ...

 




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