Adjusting the clutch...

Well constant reader, you will recall that my first attempts to adjust the clutch led to the grim discovery of a bent pedal box. Having now changed that its time to revisit clutch adjustment. Overall a worry that I hope turned out to be nothing at all- does owning a Lotus induce paranoia? I suspect so.

As summarised before the WM shows only two adjustments need to be made to the clutch; the slave cylinder push rod is adjusted so that full travel is achieved just as the pedal reaches the carpet during depression- and there is a pedal upstop that should be adjusted such that there is around 1 cm free play when the pedal is in the "up" position. In other words the distance that it can be pushed without significant resistance before it starts to move the clutch. This free play ensures that the clutch isn't being pre-loaded by the pedal. This puzzled me greatly because adjustment of the up stop itself cannot actually create this free play- it can only limit it. This is because the push rod is metal and doesn't stretch! If you set the pedal to max push rod movement at the pedal down stroke, then since the push rod is of fixed length then the  "up" position must also be fixed. Further the amount of free play obtainable is limited to the amount the push rod can move between contacting the piston inside the M/C (forward), and jamming on the stop washer (rearwards). This free play is already detectable in an isolated master cylinder independently of pedal connection. All the pedal up-stop can do is reduce this to a target of about 1-1.5 cm.

The problem I had was that even with the new pedal box, adjustment is still not obvious by these guidelines and if anyone has more insight I'd be pleased to hear.
Firstly, I found that the MC push rod needed to be adjusted to its shortest possible length in order to bottom out near the carpet- in fact if the goal is at the carpet, then the push rod just isn't short enough!
Secondly, when the push rod is adjusted to this length, then the pedal doesn't move back up far enough to contact the up-stop at all! Its upward travel is limited by the length of the push rod and available end play in the MC. This means that the pedal return spring is effectively always pulling on the push rod which I don't think can be a good situation.  I messed about with these adjustments for a while before deciding that what is going to matter ultimately is the operation of the clutch. This means setting a convenient pedal height and achieving  smooth dis/re-engagement without binding when its depressed. Disengagement is likely to occur before full depression of the pedal anyway. This can only be checked as a running adjustment when the car is mobile; so I wound the push rod back out enough that the pedal contacts the up-stop bolt to take the strain of the MC, and  decided to shelve the adjustment and tackle it again if/when the car can move.

I also attempted to bleed the clutch system. This would be easy if I had a helper, but working on my own I cannot check the exiting fluid for bubbles at the same time as pressing the pedal to expel the fluid. I decided therefore to use a vacuum bleeder, and although this was successful, it was difficult to be certain when bleeding had been achieved because air was obviously leaking in through the threads of the loosened bleed nipple and creating bubbles in the vacuum pump tubing. Once I realised this was happening I resorted to bleeding using my old Castrol bleed system; a one way valve on a tube I had bought back in the 70s! Surprisingly it still works.

At this point I got a nasty shock as the slave push-rod was not in firm contact with the clutch operating arm. The operating arm appeared to be able to flop fore and aft through a movement of around 5 cm. The slave push-rod is only app 7 cm long so this was obviously worrying, and the movement was such that the arm could be pushed back and the slave cylinder push-rod disengaged from it entirely! Looking back I'm not sure why, but I had expected the operating arm to be sprung firmly forwards against the slave push-rod by the clutch springs pushing the CRB backwards (and thus the release arm forwards).

Push-rod removed from my old slave cylinder- app 7cm.

I spent a worrying night considering how the arm could have detached from either the release bearing or the pivot point, and fretting that a gearbox  or engine removal would be needed.

However the forum was reassuring- and some members provided pictures of their own release arms in position. The next morning more thought had alleviated the worry a little: Since some cars actually have a modification in that a rearward acting assist spring is installed, it can't be that the actuating arm is always sprung forwards. The reasons for this modification seem to include assisting the push-rod in moving a very heavy clutch but also reducing noise caused by the actuating arm moving about. This has to mean that a certain amount of play in the lever is to be expected and it seems that if anything, the lever should be pulled away from the push-rod. My car wasn't fitted with a clutch arm return spring, and there is no trace of the fixing bracket suggesting that it never was. The modification seems to have been made as and when it was needed. I also found that the next day the slave push-rod was now against the release arm I think it might extend gradually on its own (under gravity?) or through my attempts at bleeding. Anyway, the operating arm was now fully back on the outside (i.e. fully forward against the clutch springs on the inside) and couldn't be pushed backwards by hand against the clutch spring. In this position the operating arm was app 4 cm from the rear of the slave cylinder and 13 cm from the front end by the bleed nipple. Access/visibility was pretty hard-to-impossible but I did get a couple of images from an endoscope.

Slave cylinder to actuating arm. You can just see that the distance with the arm pressed backwards (ie forwards against the clutch in the bell housing) is app 4 cm from lever to the groove in the slave cylinder that locates the rubber end boot.

This was a pretty similar position to that shown in the pictures on the forum. Roping in an assistant, I was able to determine that the operating arm was moving backwards when the clutch was depressed; and returning when it was released! This is all boding well for a running adjustment later when I can check if the clutch is disengaging for a smooth gearchange.

Thinking about this whole situation I think the problem was really one of simply having the wrong expectations; I had expected the clutch arm to be sprung forwards on the outside of the bell-housing but in fact its loose and floppy, and if anything, it may need to be held backwards. This being the case my clutch is probably OK: Cue massive sigh of relief... Mine's a pint!