Clutch woes - pressure lost then comes back magically, no leaks
10-24-2009, 01:42 PM
#16
Rennlist Member
Stan, that's a RHD so difficult to compare directly.
Hilton, glad to hear the hose looks good. As for waiting to do something that gives good access, when are you planning to pull the motor?
Kidding aside, when the time comes you might want to consider this approach.
Regarding the slave rebuild, if you're not getting brake fluid inside the bellhousing that's probably not the issue, though if this just started it's possible that it's leaking but hasn't made it past the boot yet.
Hilton, glad to hear the hose looks good. As for waiting to do something that gives good access, when are you planning to pull the motor?
Kidding aside, when the time comes you might want to consider this approach.Regarding the slave rebuild, if you're not getting brake fluid inside the bellhousing that's probably not the issue, though if this just started it's possible that it's leaking but hasn't made it past the boot yet.
10-24-2009, 05:32 PM
#17
Nordschleife Master
Thread Starter
Wow, quite the write-up. 
After changing the blue hose on my 87 last week, removing the whole clutch assembly is probably worth it from a time-saving point of view (blue hose wasn't too bad, but putting a hose clamp on the MC end was painful).
I think you're right on the slave - I can't see how it would suck air without leaking, being that low down.
I'm hoping the preload fix will make a difference - another symptom I hadn't thought about in a while is that I couldn't push the slave rod back into the cylinder when putting it back on after using the flywheel lock.
I posted here about it at the time, and ended up opening the bleed screw to put the clutch slave back on the bellhousing each time I had it off. Since then I bought the '87, and discovered that its actually very easy to push the slave rod in by hand, so I suspect the preload on the 89's master was preventing the return path to the reservoir opening. (might also explain why the clutch was such a bear to bleed)
Thanks for the help and input guys - I'll update after driving the car around some today, including the run to the hardware store which is my usual clutch nemesis. I'll also try and get some pics with a larger field of view to add to the thread for reference. RHD-specific threads are few and far between here
After changing the blue hose on my 87 last week, removing the whole clutch assembly is probably worth it from a time-saving point of view (blue hose wasn't too bad, but putting a hose clamp on the MC end was painful).
I think you're right on the slave - I can't see how it would suck air without leaking, being that low down.
I'm hoping the preload fix will make a difference - another symptom I hadn't thought about in a while is that I couldn't push the slave rod back into the cylinder when putting it back on after using the flywheel lock.
I posted here about it at the time, and ended up opening the bleed screw to put the clutch slave back on the bellhousing each time I had it off. Since then I bought the '87, and discovered that its actually very easy to push the slave rod in by hand, so I suspect the preload on the 89's master was preventing the return path to the reservoir opening. (might also explain why the clutch was such a bear to bleed)
Thanks for the help and input guys - I'll update after driving the car around some today, including the run to the hardware store which is my usual clutch nemesis. I'll also try and get some pics with a larger field of view to add to the thread for reference. RHD-specific threads are few and far between here
Stan, that's a RHD so difficult to compare directly.
Hilton, glad to hear the hose looks good. As for waiting to do something that gives good access, when are you planning to pull the motor? Kidding aside, when the time comes you might want to consider this approach.
Regarding the slave rebuild, if you're not getting brake fluid inside the bellhousing that's probably not the issue, though if this just started it's possible that it's leaking but hasn't made it past the boot yet.
Hilton, glad to hear the hose looks good. As for waiting to do something that gives good access, when are you planning to pull the motor?
Kidding aside, when the time comes you might want to consider this approach.Regarding the slave rebuild, if you're not getting brake fluid inside the bellhousing that's probably not the issue, though if this just started it's possible that it's leaking but hasn't made it past the boot yet.
10-24-2009, 06:01 PM
#18
Team Owner
if you cant push the rod back into the slave then the MC isnt releasing all the way as the return port is blocked
10-25-2009, 07:41 AM
#20
Nordschleife Master
Thread Starter
Well, after a day of driving around, no dead clutch pedal. However, its cold today.. 17 degrees C. When it happened the other day it was ambient 32 degrees C (90 degrees F). I'll drive it around for a few days and see how it goes - worst is I have to drive home without a clutch 
Since adjusting the helper spring, and also the preload on the clutch master, the clutch action has improved. Much lighter and smoother, and I took the slave off to push the rod and it goes in easily, so the return path wasn't opening before. So even if the clutch goes dead (likely I suspect), I've still had a couple of wins so far
Will update once I've had a few drives in warmer weather - this cold front is set to be here a couple of days.
Since adjusting the helper spring, and also the preload on the clutch master, the clutch action has improved. Much lighter and smoother, and I took the slave off to push the rod and it goes in easily, so the return path wasn't opening before. So even if the clutch goes dead (likely I suspect), I've still had a couple of wins so far
Will update once I've had a few drives in warmer weather - this cold front is set to be here a couple of days.
10-25-2009, 05:41 PM
#21
Addict
Rennlist Member
Rennlist Member
When I completed the $50 GT refurb in 2004 the clutch slave cylinder was a pile of frozen rust, so i replaced it.
I have now driven the car 18,000 miles in the last 5 years with the clutch working perfectly. The brake/clutch fluid has been flushed every 2 years. On the way to the FRENZY this year, I stopped to pay a toll and then accelerated through first second and third perfectly. When I went to shift to forth, the clutch pedal was on the floor. But the clutch was engaged? And I was accelerating in third gear? I reached down and retrieved the clutch pedal and shifted into forth gear. The clutch has worked perfectly ever since.
I mentioned this to several people at the FRENZY and both said this was normal and was caused by an air bubble in the fluid. That does not make sense to me. A one time failure of the master cylinder maybe?
I have now driven the car 18,000 miles in the last 5 years with the clutch working perfectly. The brake/clutch fluid has been flushed every 2 years. On the way to the FRENZY this year, I stopped to pay a toll and then accelerated through first second and third perfectly. When I went to shift to forth, the clutch pedal was on the floor. But the clutch was engaged? And I was accelerating in third gear? I reached down and retrieved the clutch pedal and shifted into forth gear. The clutch has worked perfectly ever since.
I mentioned this to several people at the FRENZY and both said this was normal and was caused by an air bubble in the fluid. That does not make sense to me. A one time failure of the master cylinder maybe?
10-25-2009, 08:54 PM
#22
Team Owner
Capt Earl you might be on borrowed time with the clutch MC.
When your new one arrives see if the bore is good in your old cylinder, and use the seals from the new part as the pistons are shorter in the new versions and may not give you full release.
The other option is to cut the end of the piston off and file a slot in it IIRC you remove about 3 to 4 MM of metal.
Measure first..
You may be able to leave the MC housing in the car and just remove the guts
When your new one arrives see if the bore is good in your old cylinder, and use the seals from the new part as the pistons are shorter in the new versions and may not give you full release.
The other option is to cut the end of the piston off and file a slot in it IIRC you remove about 3 to 4 MM of metal.
Measure first..
You may be able to leave the MC housing in the car and just remove the guts
10-26-2009, 10:54 AM
#23
Supercharged
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When I completed the $50 GT refurb in 2004 the clutch slave cylinder was a pile of frozen rust, so i replaced it.
I have now driven the car 18,000 miles in the last 5 years with the clutch working perfectly. The brake/clutch fluid has been flushed every 2 years. On the way to the FRENZY this year, I stopped to pay a toll and then accelerated through first second and third perfectly. When I went to shift to forth, the clutch pedal was on the floor. But the clutch was engaged? And I was accelerating in third gear? I reached down and retrieved the clutch pedal and shifted into forth gear. The clutch has worked perfectly ever since.
I mentioned this to several people at the FRENZY and both said this was normal and was caused by an air bubble in the fluid. That does not make sense to me. A one time failure of the master cylinder maybe?
I have now driven the car 18,000 miles in the last 5 years with the clutch working perfectly. The brake/clutch fluid has been flushed every 2 years. On the way to the FRENZY this year, I stopped to pay a toll and then accelerated through first second and third perfectly. When I went to shift to forth, the clutch pedal was on the floor. But the clutch was engaged? And I was accelerating in third gear? I reached down and retrieved the clutch pedal and shifted into forth gear. The clutch has worked perfectly ever since.
I mentioned this to several people at the FRENZY and both said this was normal and was caused by an air bubble in the fluid. That does not make sense to me. A one time failure of the master cylinder maybe?
10-26-2009, 11:48 AM
#24
I had identical symptoms: sometimes after the car had been sitting with the engine off (and only after it had been run long enough to get everything warmed up) the clutch would function properly a few times but would then stay on the floor after being pushed, held by the helper spring. There was little effort required to press the pedal down when it failed this way: just enough pressure and movement to get past the over center on the helper spring.
The clutch would usually work properly after pulling the pedal back up. Devek (yes, this was awhile ago...) bled the clutch using the step-on-the-pedal method, which did not cure the problem. The problem went away after I got a power bleeder and thoroughly flushed the clutch hydraulics. No problems since.
FWIW, I presumed that the problem was water contaminating the brake fluid that would boil when the engine bay heat soaked while setting, and not an air bubble as the clutch pedal was always solid except when it went on strike. I had thought about fabricating a heat shield as the hose and tubing are very close to the Devek headers ( maybe less room than with stock?), but did not as the problem has not recurred.
Good luck
The clutch would usually work properly after pulling the pedal back up. Devek (yes, this was awhile ago...) bled the clutch using the step-on-the-pedal method, which did not cure the problem. The problem went away after I got a power bleeder and thoroughly flushed the clutch hydraulics. No problems since.
FWIW, I presumed that the problem was water contaminating the brake fluid that would boil when the engine bay heat soaked while setting, and not an air bubble as the clutch pedal was always solid except when it went on strike. I had thought about fabricating a heat shield as the hose and tubing are very close to the Devek headers ( maybe less room than with stock?), but did not as the problem has not recurred.
Good luck
