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Because this seems like such famous issue, when re-building the master cylinder didn't do the job, I decided to just fit a new one, but, because of everything I've read I decided to go for a 3/4 bore cylinder rather than the standard 5/8 in an effort to move more fluid and less prone to drag. Being only a little guy I hoped it would not make the pedal too stiff.

Well it has worked well (so far) yes it's a bit stiffer but not much clearance is better especially into first or reverse. I'd say it's a good fix.

Roger :thumbsup:

Life is like a sewer, what you get out of it, depends on what you put into it. (Tom Leahrer)

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Hi All,

IMHO you should be very carefull when increasing the master cylinder's diameter on a clutch system. What you did is going from original 3/4" to 5/8" diameter (metric: 16mm to 19mm). This is an increase by 40% in area and volume ! This should increase your slave cylinder travel quite noticable.

What makes me a bit nervous is the fact that if everything with your clutch setup is 100% and the fork adjusted up to spec (9-12mm) then you should get too much travel there !

Either you have compensated that with a differnet fork adjustement (5-8mm for example) OR you still have air in your system ... I personally believe that there is still some air ...

Cheers

Marcus

Edited by Paula&Marcus

Marcus

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Marcus is correct. Over extending your diaphram will fatigue it resulting in pre-mature failure. Lotus also have set the specs so there is minimal likelihood of damaging the flywheel face once the clutch is worn out.

You can reset the travel to the original amount by marking the positions of the throw-out fork to the bellhousing opening BUT you would need the original set-up to establish your reference points. Alternatively find out what the thrust travel of the diaphram is, remove your gearbox and work it out from there. Mark on the bellhousing opening the fork's position for every 5mm of throwout bearing travel. Then set up the slave clearance to suit.

All doable but probably safer to stick to the original master cylinder.

DanR

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I don't appear to be getting too much travel, ample and no drag but not too much, I did check it first. I suspect at 56000 miles the clutch is on its last legs, but it's not slipping yet, but when I fit a new one I will take note of your comments. Interestingly there are two holes in the clutch pedal for the push rod to the cylinder one being slightly higher, there for slightly less travel, anyone tried the second option.

Roger :)

I suppose I should add that I am fussy about pedal hight, both rest and actuate, being a short A, at 5' 4" I find it hard to hold the clutch pedal to the floor, ie traffic lights. so I don't like to use the full pedal travel.

Edited by Roger Harris

Life is like a sewer, what you get out of it, depends on what you put into it. (Tom Leahrer)

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Hai roger,

If I remember correctly the holes are marked B and C. When the pedal is in use as Brake pedal you have to use the B marked hole and for use as Clutch pedal it will be the C marked hole. The two pedals are the same.

Freek.

Esprit Freak

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I don't appear to be getting too much travel, ample and no drag but not too much, I did check it first. I suspect at 56000 miles the clutch is on its last legs, but it's not slipping yet, but when I fit a new one I will take note of your comments. Interestingly there are two holes in the clutch pedal for the push rod to the cylinder one being slightly higher, there for slightly less travel, anyone tried the second option.

Roger :)

I suppose I should add that I am fussy about pedal hight, both rest and actuate, being a short A, at 5' 4" I find it hard to hold the clutch pedal to the floor, ie traffic lights. so I don't like to use the full pedal travel.

Roger,

In using a larger bore mc you should also be using a different length pushrod at the slave. Lotus used different lengths for the 5/8 bore in earlier cars and .70 bore used in later cars and different setup specs. If you don't follow the recommended setup specs it's possible to damage your flywheel before the clutch actually slips as well as the overtravel problem that Marcus mentioned.

Overtravel can also cause the shifting problems I think you mentioned in another thread.

FWIW, you mentioned holding the clutch to the floor at traffic lights, etc. It is recommended to put the tranny in neutral and hold the brake when stopped as holding the clutch pedal to the floor causes excessive wear on the release bearing.

Cheers,

1995 S4s

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And a potentially more serious problem than a worn release bearing can be a worn thrust bearing inside the engine resulting in excessive crank end float!

DanR

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Whilst in no way detracting from any comments all of which I am grateful for and have noted and investigated. For the first time since buying the car, having already rebuilt the slave cylinder, checked the braided hose, rebuilt before disguarding the master cylinder and replacing it. I can at last get it into both first and reverse without grating, and hold it out without draging.

It is more than possible that I have compensated for poor driving technique, hate stretching for the pedals, or a short coming in the clutch, I cannot adjust the push rod due to rust, I'm a bit scared to swing on a spanner, since I don't yet know how the fort is located within the gearbox, and until the clutch fails, I see insuficent cause to find out.

Life is like a sewer, what you get out of it, depends on what you put into it. (Tom Leahrer)

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Roger, if I'm reading you correctly, it seems to me that your main concern is about the amount of pedal pressure you have to apply to effect a release of the clutch plate. The important factors here are, I believe, the movement and force applied by your foot and the amount of slave cylinder piston movement it produces. The force required to disengage the clutch, at the clutch itself, is a constant dictated by the mechanical characteristics of the clutch as is the distance that the clutch operating arm has to move to bring that about.

As mentioned in a previous post, just increasing the slave piston movement could cause damage within the clutch itself so the problem is how to do it while keeping the clutch movement within its design parameters.

If you are pumping more fluid from a larger master cylinder, for the same pedal depression, then you need to reduce the travel of the master cylinder piston to bring it back to delivering the same volume of fluid as the previous cylinder did. This is best achieved by reducing the length between the pedal pivot point and the master cylinder piston pivot point. The distance between the pedal and the pedal pivot point will also need to be increased to produce an 'easier' pedal to counteract the shortening of the other length.

There are some fairly rudimentary, tedious and iterative calculations you can make to decide where the various pivot points need to be placed but to achieve them you may be looking at having to replace your pedal as Sods Law probably dictates that the position for the new pivot point hole won't be possible without fouling the existing 'B' and 'C' holes.

In theory there is no difference between theory and practice.<br />

<br />

In practice, there is!

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