Lotus Elan

Clutch slave piston travel

PostPost by: tonyabacus » Mon Jun 22, 2020 2:52 pm

Overhauled both clutch master and slave cylinders with new rubbers and checked all parts before re installing. Have adjusted as the manual and seemed to bleed through okay. However when rechecking the slave clearance with wife operating the pedal, I noticed that the rubber cover over the end of the slave had popped off, so refitted it and asked wife to operate pedal to verify all was okay. Again the rubber cover popped off and with pedal pressed down it seemed the piston on the slave was coming a distance out of the cylinder. I may have been a bit to plentiful with the grease around the operating rod inside the cover, which may be part of the reason why the rubber slips off.

Both cylinders are the standard sizes and once bled the pedal appears to operate as it should. Not able to road test or engine test as some of the electrics are fitted and operational.

So my question is, is this normal and by how much should the piston project out of the slave cylinder in normal operation, is anyone able to do a comparative measure for me please?
Tony
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PostPost by: 2cams70 » Mon Jun 22, 2020 3:07 pm

Pedal pumping wives, slaves and rubbers popping off pistons - are you sure you are on the correct forum!!??
Perhaps you could post a picture of that miscreant piston so we can diagnose (then again - maybe don't!)
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PostPost by: snowyelan » Mon Jun 22, 2020 3:47 pm

Sounds like the slave rod isn't adjusted properly (too short). Can you push the rod further into the slave?
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PostPost by: alanr » Mon Jun 22, 2020 4:20 pm

Sounds like the circlip is not in its groove and holding the cylinder in its correct position in the bellhousing either due to the push rod adjustment not being correct ( approx 1/8th of an inch max) or the circlip is just the wrong size or stretched maybe and again not holding the cylinder in position in the bellhousing.

Alan.
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PostPost by: joe7 » Mon Jun 22, 2020 7:23 pm

I'll go with Alan. There are 2 grooves one for the dust cap and one for the circlip.
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PostPost by: tonyabacus » Tue Jun 23, 2020 1:40 am

Thanks for the replies,
1. I measured the circlip and groove before fitting back into the car, the groove being just a few thou wider than the circlip, but only sufficient to provide clearance.
2. The circlip is correct and in the correct groove, when fitted in the car there is a small amount of movement between the circlip and the holder, perhaps wide enough to take another circlip, but this seems about normal from some of the previous discussions here on the subject.
3. When the pedal is operated the circlip remains in its groove, so appears to be doing its job correctly
4. I note there has been discussions on the book setting for the clearance, so what have others found to be the correct setting
5. Joe, the two grooves mentioned by Alan are some distance apart so can confirm that as above the circlip is in the correct groove
6. The circlip is new from a Lotus specialist
6. Snowy, will need to get back under to check for your suggestion, so will do that and report back

I think I only noticed the piston protruding so far because the end rubber cap had slipped off, normally when the cover is held in place you would not know or see how far the piston moves within the cylinder and end cover, hence my original question is anyone able to check this on their car to see how far the piston moves.
Thanks for the input guys
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PostPost by: 2cams70 » Tue Jun 23, 2020 2:37 am

If the pushrod adjustment is eliminated as a cause check the slave cylinder piston diameter to ensure you have the correct cylinder fitted. The Ford Anglia slave cylinder is identical in appearance to the Lotus one except for the piston diameter which is slightly smaller. If you have used the Anglia slave cylinder in place of the correct Lotus one the stroke of the piston will be longer than is should be. Correct slave cylinder bore diameter for the Lotus is 0.875" (22mm). It's easy for suppliers to make a mistake.
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PostPost by: Noel+2 » Tue Jun 23, 2020 9:48 am

Could just be air trapped between the piston and the rubber cover, as the piston comes out it pushes the cover off. Some covers have a small air hole some don't.
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PostPost by: tonyabacus » Tue Jun 23, 2020 10:48 pm

Thanks all for responses, for clarification both cylinders were those already fitted to the car which after thorough checking for wear and any potential score marks etc I decided to refurbish. The kits came from one of the established Lotus specialists and were installed with the correct Girling red grease.

Before doing the work I checked on the forums to check for any known issues so was prepared for the Anglia problem, but both the master and slave cylinders are the correct items with correct sizes. Mine is also the later set up with the steel pipe that links the slave to the preceding flexi, which by the way also checked out as good. The system also as previously stated bled very easy with none of the usual air issues, so got a good pedal more or less straight away.

Noel, I checked tonight and the rubber cover supplied does not have a "breather" hole in it so may consider doing that, at same time rechecked the tolerance on the pushrod and decided that whilst it appeared correct I have backed the adjustment off about a third of a turn so that there is a faint rattle to the setting as suggested elsewhere in the forum.

Originally I put a small amount of the red grease inside the slave cover so that the rod could move in and out without being dry and possibly pulling the cover off. So I have tonight cleaned around the edge of the cover seal and the body of the cylinder to make sure that the cover to cylinder surfaces are dry and not slipping off due to being greasy.

So that is as far as I have got tonight, whilst the pedal feels good I am still slightly baffled at the piston travel in the slave, so again if anyone is doing a rebuild and can take off the slave cover and check the travel on their car I would be interested to know how much travel they get.

Having searched the forums I can't find any past concerns with the piston popping out during use, especially as we know that even with the correct circlip in place, the small gap that remains has been a bone of contention on the forum for a number of years. My own theory on the gap issue is that it exists to overcome any manufacturing tolerances on the bell housings, as the small residual gap after fitting the circlip takes care of such tolerance problems, rather than having a potential "interference fit" between the circlip and the bellhousing slave mounting hole which would cause bigger problems in service. Comment welcomed.
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PostPost by: lotusfan » Tue Jun 23, 2020 11:15 pm

Hi Tony

You say you have searched the forums and can't find any past concerns with the piston popping out during use. Have you seen my epistle which was caused by bad initial setting up?

viewtopic.php?t=25748

it may help.
Mike
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PostPost by: tonyabacus » Wed Jun 24, 2020 11:18 am

Hi Mike
Thanks, despite trawling the forums I did not come across your experience and the subsequent solution.

I set the clearance according to the WSM, and to date have set and rechecked it four times and on the last occasion set it without feelers so that there was the faintest rattle from the rod indicating that it was not too tight (as per another suggestion on the forum). One might also be forgiven for thinking that when bleeding for the first time, that when opening the bleed nipple that the return spring would pull the piston back down the cylinder to a degree.

However your photo and notes are of value and I shall be back under later to recheck once again and report back. I think there cannot be many issues that others have not come across and reported in the forum over the years, the problem is finding them, so thanks again for responding to my question and pointing me in the right direction, will report back asap.
Regards
Tony
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PostPost by: tonyabacus » Fri Jul 03, 2020 12:39 pm

An update on the issue.

You may recall that the clutch slave piston appeared to be coming a long way out of the cylinder making me concerned about it popping out. Despite bleeding again and rechecking the clearance, whilst having a good pedal and an operating clutch I was still concerned. So off came the cylinder and taken apart once more to recheck, all appeared good but no immediate problem identified so reassembled. However once together I noticed that the internal helper spring was obviously pushing the piston out along the bore as intended which then set me thinking.

So putting the cylinder back in the car I checked the position of the rod as I was setting up the clearance, question, which comes first the setting of the clearance or the bleeding? When originally disassembling I had not taken much notice of the length of the rod to the adjusting nut so now had no primary setting for the rod to enable bleeding to take place. So I decided on an arbitrary length that pushed the piston a good way down the cylinder and attached the outer spring. Bled the system of all the air and then set the final clearance, all now seems fine with the piston remaining well inside the cylinder.

I can only conclude that when setting up the first time round that I had not noticed that the piston had not been pushed back far enough into the cylinder, due to not setting a sufficient arbitrary distance of the operating rod. So that once bled the slave cylinder was full of fluid but the piston was too far along the cylinder. It was still possible to get a clearance gap on the rod in this position due to the available threaded length of the rod, but of course when operating the clutch pedal the piston was already so far along that it emerged from the cylinder to a degree.

Lesson learned, the WSM explains how to set the clearance when the system is already bled but makes no mention of when completely empty after a refurb. You need to either take a note of the length of the rod from piston to adjusting nut before disassembling or set an arbitrary distance before the initial bleed, otherwise the internal helper spring will do its job and hold the piston a distance along the bore, which no amount of bleeding can overcome. So set the rod and make sure the piston is a good distance along the bore which can be checked by inserting a long thin screwdriver into the cylinder and pressing against the piston and spring before starting to bleed the system. In reality the piston does not travel too far during normal operation, you can see how far by observing the clutch arm travel as the pedal is operated over its full travel and by relating that distance to the distance measured along your screwdriver will give comfort that all is well.

I hope this along with the clues provided in Mike's case above helps others and saves hours of head scratching.
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PostPost by: oldelanman » Fri Jul 03, 2020 2:29 pm

tonyabacus wrote:However once together I noticed that the internal helper spring was obviously pushing the piston out along the bore as intended which then set me thinking.


You may have the wrong slave cylinder....there should not be a spring inside. At rest the slave piston should be fully seated in the bore and the push rod should be adjusted in that condition .. with the external return spring removed (the one between the release arm and the slave cylinder body) .. it does not matter if the system has been bled or not.

Clutch Slave.jpg and
No internal spring
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