Lotus Elan

Clutch slave cylinder piston pushed out

PostPost by: lotusfan » Mon Jul 23, 2012 5:25 pm

Gentlemen

Can I seek your collected wisdom on an issue I have had with the clutch on my freshly refurbished Sprint. It had an MOT for the first time in 10 years last week and then I had about 100 very pleasurable miles including a trip to the Silverstone Classic.

During a local trip the clutch pedal went to the floor with no ?feel? and it was possible to select any gear with the engine running without crunching the gears. Inspection showed no fluid in the master cylinder and a pool of oil under the car. It was not possible to get under and see the slave cylinder because of it?s location. I suffered the ignominy of being towed home by the RAC. Having got it home and jacked up I could see that the slave cylinder piston was out of the cylinder, jammed at an angle, holding the clutch out.

So the question is ?why?? All clutch components are new, the slave and master cylinder are the correct sizes and the master cylinder push rod is the correct length according to Brian Buckland?s book, the slave push rod was set to 2 mm clearance.

I believe a clue is a black line on the engine bulkhead where the clutch pedal arm was contacting the bulkhead. The felt and carpet are not yet fitted and maybe this is the reason, if they were there the pedal travel would be less.

As a temporary fix I was going to fix a thin block of wood to the clutch pedal arm to limit the travel but I wonder if a permanent stop of some sort would be needed even after the carpets are fitted.

Comments please, have I missed anything?
Mike
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PostPost by: UAB807F » Mon Jul 23, 2012 8:51 pm

My first thoughts were an oversized m/cyl being inadvertently supplied but I see that's ruled that out.

My next thoughts are around the fluid not fully returning on each use of the clutch, either the m/cyl or slave cyl. piston sticking and hence allowing some fluid build up in the system so the next time it's moved slightly more and eventually ramps itself out of the bore.

Thinking about the carpet theory and over-travel, then surely if that were the case then the very first time the clutch was depressed fully you'd have blown it out ? But you managed quite a few miles before failure so that makes me think it's a gradual problem.

I think I'd start off by re-assembling everything but leaving the top off the clutch m/cyl and operating the clutch a few times to see if the fluid level in the m/cyl returns to the same level after pedal release or drops over say 20-30 applications ?

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PostPost by: robertverhey » Mon Jul 23, 2012 10:01 pm

I'm intrigued by this:

"the clutch pedal went to the floor with no ?feel? and it was possible to select any gear with the engine running without crunching the gears".

Sounds like something major awry in the pressure plate? Would a broken diaphragm spring mean the clutch was always engaged (ie no contact between flywheel and PP facings), and the lack of usual resistance from the diaphragm spring allowed the piston in the slave cylinder to just keep going and pop out?

Well that's my long distance thoughts
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PostPost by: neilsjuke » Mon Jul 23, 2012 10:11 pm

Bent or cracked release arm
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PostPost by: robertverhey » Mon Jul 23, 2012 10:36 pm

But broken/ bent arm would leave clutch connected, wouldn't it? Trying to think of a fault that would leave clutch permanently "in" even without pedal pressed in.....hence ability to select gears with motor running......
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PostPost by: ardee_selby » Mon Jul 23, 2012 10:41 pm

lotusfan wrote: Having got it home and jacked up I could see that the slave cylinder piston was out of the cylinder...


Your problem rang a bell...

"On inspection it seems like the piston in the slave cylinder has been pushed right out of the cylinder..."

The above quote is from (elan-archive-f16/sudden-clutch-failure-t13047.html) which, as Neil has suggested, was caused by a release arm failure... :(

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PostPost by: Robbie693 » Tue Jul 24, 2012 9:06 am

robertverhey wrote:But broken/ bent arm would leave clutch connected, wouldn't it? Trying to think of a fault that would leave clutch permanently "in" even without pedal pressed in.....hence ability to select gears with motor running......


This confused me too - I think Mike made a typo, should have read IMpossible...?

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PostPost by: john.p.clegg » Tue Jul 24, 2012 9:15 am

If the return spring on the operating arm had dropped off,the arm/rod and piston would not be forced to return fully??

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PostPost by: Hawksfield » Tue Jul 24, 2012 9:26 am

Lotusfan

Check the flexible hose if its old but looks OK it can be swollen internally as happened to me, its like a one way valve.
I had to change mine due to this and also I changed the the brake flixible hoses as a precaution before they gave trouble.

GOOD LUCK
Regards

John

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PostPost by: lotusfan » Tue Jul 24, 2012 5:06 pm

Thank you all very much for your comments.

Richard - there is no conclusion to the archive thread, was it actually release arm failure?

Robbie - no typo, I can run the engine and select any gear - the clutch is disengaged.

John - the rod return spring is there.

Hawksfield - the hose is new, Goodridge braided hose, but an interesting theory.

The car is currently up on ramps in the garage and I will investigate further this coming weekend and report back, if possible I will post a photo of the slave cylinder.

Because the clutch is disengaged I do not think any release arms bits or diaphragm fingers are broken. My view is still that once the piston is back in the cylinder and the system is bled we will be good to go - we will see. I will follow Brian's advice re watching the master cylinder level.
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PostPost by: ardee_selby » Tue Jul 24, 2012 5:57 pm

lotusfan wrote:Thank you all very much for your comments.

Richard - there is no conclusion to the archive thread, was it actually release arm failure?


Yes, unfortunately. Pete followed up with the "fix" in this thread:

elan-f15/clutch-release-bearing-attachment-t14501.html

"Last year- two weeks before I set off for the Le Mans Classics (!) my clutch release fork failed, it split into two pieces with the failure line between the spring holes. Got a new fork and bits from Matty (btw, the new fork is much stronger than the old standard pressed part, being thicker gauge material and welded rather than stamped out). I had the very devil of a job trying to get the new "big" spring to go back into place' when I eventually compared it to the old one I found that the little straight bits on the ends (see Brian's photo) were just a bit longer. 2 sec on the bench grinder and it all went together!"

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PostPost by: neilsjuke » Tue Jul 24, 2012 9:15 pm

Bent or cracked release arm

If the arm has broken at the pivot point it may have jammed the release bearing .
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PostPost by: robertverhey » Tue Jul 24, 2012 10:52 pm

Had a Renault 12 way back when. The clutch diaphragm spring split right across, from one side to the other. Symptoms were similar....a box full of neutrals. Anyway worth trying to fix the slave first, you never know your luck. Neil's release bearing jammed is also a distinct possibility. Hope I'm wrong but I suspect it's engine out time.
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PostPost by: RotoFlexible » Fri Jul 27, 2012 3:25 pm

lotusfan wrote:Inspection showed no fluid in the master cylinder and a pool of oil under the car. ... Having got it home and jacked up I could see that the slave cylinder piston was out of the cylinder, jammed at an angle, holding the clutch out.

This would explain the "box full of neutrals." I think everything was fine for a while, then for some reason (slave piston stuck, or fluid didn't flow back into the M/C) the slave piston didn't retract fully when the clutch pedal was released. The next push on the pedal pushed the piston all the way out of the slave, where it cocked and jammed, and also dumped the hydraulic fluid on the ground.

Either that, or a catastrophic failure of the clutch or release bearing, as posited by others. If the release arm is holding strong tension against the rod and piston, then the clutch and release mechanism are probably OK.
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PostPost by: lotusfan » Mon Jul 30, 2012 9:26 am

Update Gentlemen ? photo attached of the slave cylinder, you can see that the piston is cocked at an angle and the boot is free. The other thing that may not be obvious is that the pivot nut and locknut are at the extreme end of the thread closest to the piston.

I tried levering the piston and push rod but failed so decided to cut through the push rod having tied the release arm back to the gearbox mount. This then freed it up and I could push the piston back into the cylinder. I removed the release arm rubber boot and looked inside to see the mechanism, it all looked good, the release arm was in one piece, the spring clip was still holding the arm in place and the release bearing was still there. Levering the release arm manually gave the correct, over centre, diaphragm ?feel?.

Having temporarily repositioned the pieces of push rod there was a gap of about ? inch between the two pieces. I removed the slave cylinder and there was a small area of damage at the open end probably caused by trying to lever the piston back into place. There were also some axial lines caused by the piston moving but concentrated towards the open end of the cylinder.

My working hypothesis for the failure is now that when I set the 2 mm gap between the push rod and release lever the piston was not pushed fully down into the cylinder because I had not removed the bung from the hose connection. The gap was set on the bench without the hose connected before the engine and gearbox went into the chassis. The return spring will pull the release bearing away from the clutch but it won?t push the piston all the way down the cylinder bore if the 2mm gap is too big thus the piston was operating towards the open end of the cylinder as evidenced by the axial lines and it was only a matter of time before it sought freedom.

Lesson learnt I think, make sure the piston is all the way home. The plan is to replace the piston seal as a precaution and fit a new push rod and make sure that there is some thread left when the adjustment is set.
Attachments
clutch slave compressed.jpg and
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