Clutch adjustment

[vikla]

My clutch operation has always been at the top of the pedal travel and is pretty stiff (probably due to being an old spring clutch fitted the late 70's).

Even though my engine no. suggests the car should originally have had the longer 95mm slave cylinder, it had on it a leaking 80mm slave but without an external spring.

I have just had the slave cylinder replaced by E-Type specialists.
Firstly they put on a new 80mm unit but when they went to bleed it the piston shot out of the cylinder when the pedal was depressed. They seemed surprised by this. They did comment that the old one had a circlip in it which would have stopped the cylinder piston movement. (Subsequently I see that the slaves should have a circlip in them, so was the one they fitted a faulty one ?!). They also mentioned stuff about the master cylinder re. bore size and about Girling units.
Anyway they then decided to fit a 95mm slave unit instead, seemingly on the basis it accommodates more piston travel. When I got the car back they said it was now OK but the pedal was a bit high.

The clutch pedal was about 15-20mm higher than the brake pedal which was rather awkward to use. I have just had a go at adjusting the actuating rod length and made a bit of difference in reducing pedal height but wasn't too sure whether to shorten or lengthen the rod.

I also wonder whether the garage adjusted the rod travel as per Jaguar instructions .




Regarding the master cylinder I do not know what mine is. I see that in the XKs Unlimited catalogue they suggest if a Girling mc is used then a spacer (item 15 below) should be fitted to get the correct pedal height.




Any comments would be welcome on reducing the pedal height, e.g. which way to adjust the slave rod and also about spacers on the master cylinder.

Thanks

[chrisvine]

Steve,

Did you manage to resolve the clutch pedal height issue? I've also encountered the same problem where the clutch pedal is approx. 2cm higher than the brake pedal.

The master cylinder has the correct spacer (part 15 in the diagram) and the 95mm (non-hydrostatic) slave cylinder has been adjusted as per the service manual. The stop for the brake pedal was set so its push rod immediately engages with the master cylinder piston.

As far as I can work out, the height of the clutch pedal is limited by the washer around the push rod end hitting the retaining circlip. Therefore the height is effectively set by the spacer.

Any help would be appreciated.

Chris

[JEP41]

I recently replaced the clutch master cylinder with a new Girling type from SNG Barratt. However the one removed which I assume was fitted by the PO was a Wilwood and I to noticed the clutch pedal was then too high and didn't align with the Brake Pedal. I found the Girling master cylinder rod was approx. 1/2" longer than the wildwood rod. Solution I swopped the rods over and the pedals aligned problem solved.

[vikla]

Steve,

Did you manage to resolve the clutch pedal height issue? I've also encountered the same problem where the clutch pedal is approx. 2cm higher than the brake pedal.

Chris,

I'm afraid I didn't.
I tried a variety of adjustments but in the end gave up.
So like you I am still looking for a solution.
Perhaps the length of the rod is the crucial factor.
I will look again in the near future.

[abowie]

I'm a bit tired having had a disturbed night with work, but won't the pedal height be set by the apparent length of the master cylinder actuating rod?

From memory the cylinder end of the rod is held into the end of the cylinder with a circlip which limits how far out it can come. The other end of the rod has a yoke which is pinned to the (spring loaded) clutch pedal. The spring on the pedal tends to pull the pedal up from the floor. This pulls the actuating rod back until it hits the circlip and can go no further, stopping the pedal travel.

To drop the pedal down, you need either to shorten the rod or to put a thicker shim in between the pedal box and the master cylinder which moves the end of the cylinder and therefore the circlip further away. Because of the lever arm effect a small change in the actuating rod effective length will make a much larger difference in pedal position, so you might only need to be 3mm out on your shim to put the pedal 20mm too high.

As shimming the cylinder is a lot easier than cutting and shutting the rod, try loosening the 2 nuts that locate master cylinder and shimming it out by wedging a couple of washers in the gap between the master cylinder and the pedal box (or shim if fitted). See how this changes the pedal height. Once you know exactly how thich the shim needs to be you can make up an appropriate one.

As far as I can determine in my slightly hazy state changes with the slave cylinder or it's adjusting rod should not affect the resting position of the pedal at all...

[chrisvine]

All,

Thanks for the responses. I came to the same conclusion as Andrew & John, that the problem lies with the length of the master cylinder push rod. The adjustment of the slave cylinder push rod is irrelevant.

I was planning to re-weld the master cylinder push rod but it would be much easier to do as you suggest and add additional spacers. So thanks for that. My folk came with the replacement master cylinder so I think it's too long.

Chris

[vikla]

I have investigated my master cylinder.
It is marked Girling - does that mean it is a replacement for an original Dunlop one (S1 4.2 1966)?
It does not have a spacer, so I undid the nuts and put in a 3mm bit of material to space it out. This has helped a little with the pedal height.
(Difficult to get anything under the lower part because access is very difficult.)

It's interesting that I started this thread because my pedal height went up after the slave cylinder was changed - the master wasn't touched. So that seems slightly at odds with the general conclusion that pedal height is only affected by the master cylinder rod length....

[mgcjag]

Hi guys...just a thought....if there was no fluid in the system so nothing to hold the piston/pushrod on the master then the weight of the pedel would drop down and be held by the strength of the return spring. So pedle height is affected by the fluid in the system if u replace the slave and the pedle height alters it could be that previously there was air in the slave.....not saying this is correct but what do u think?...Steve

[abowie]

Steve the clutch return spring lifts the pedal up. It is strong enough to overcome the weight of the pedal. If there was no fluid in the system the clutch wouldn't operate anyway so that would become clear quickly..

Vikla the standard spacer is about 8mm from memory; I don't have one to hand to measure ATM. I honestly can't explain how changing the slave cylinder could raise the pedal. The only thing I can suggest is that perhaps the old cylinder allowed the pedal to sit low by virtue of not pushing the master cylinder piston all the way back. If it had leaked fluid out maybe this is possible although you would think that the cylinder would refill itself from the reservoir. This could only work though if your clutch pedal spring was broken...which they commonly do.

[abowie]

The clutch slave cylinders have always been a bit of a mystery to me.
My assumption is that there are different sizes because the throw of the clutch fork differs on some cars.
I have always assumed that the adjustment on the rod is purely to allow for a small amount of freeplay so that the clutch isn't permanently actuated when driving. This would also allow for peroidic adjustment as the solid thrust bearing wears down.
I have no good concept of why some units require a return spring and others don't. It seems to me that the strength of the springs in the clutch itself are more than enough to push the piston back out again. I don't understand what the term "hydrostatic" means when applied to the slacve cylinders.
I'd love to hear from someone who actually understands why.

[mgcjag]

Andrew....I think that u totally misread my post....and then answered what i was saying ....the pedel is only higher since tha slave was replaced, so this seems to indicate that the fluid in the system is pushing the pedel higher....could it be that the peddel was to low previously....or as u say the return spring week/broken...which is common..and the rebleed system is pushing the master pushrod fully back and thus the pedel higher....Steve

[vikla]

Looks like I need to go and check if my pedal return spring is broken. However it looks like a big job to replace - strip out all the pedal box?

I consulted Clausager's originality book to see what changes have been made regarding clutch cylinders.



Very interesting that 3 major changes were made; to the pedal box, the pedal angle and the master cylinder, all in just over a year.
My car sits between the first two changes so maybe affected by having an early pedal box and pedal and a later Girling cylinder.
No wonder this turns out to be not straightforward...

[andrewh]

wrestling with this issue at the moment. I have discovered that the pushrod is the key to pedal height. I think this thread had concluded that but for clarity , the pushrod from my original Dunlop master is the correct length. The new MC is a different bore and requires a pushrod with a smaller diameter locating washer. The one supplied that fits is now much longer and holds the pedal too far up. SNG offer a spacer to bring the pedal back down to the correct height. Only the studs not he pedal box are not long enough and did I read somewhere that the clutch master can get mighty close to the rear carb? How a ten minute job takes half a day!