Clutch hydraulic gearing

[Steve1967]

Hi, I have recently started my engine for the first time and bled the clutch. All good!

I've not had an E Type before but the clutch feels OK, but fairly heavy. Certainly if it were possible at this stage to do something about it I would.

I wondered whether it would be possible to fit a slightly larger diameter slave cylinder to improve the hydraulic gearing giving a lighter pedal? I would rather not mess with the master cylinder as thats a lot of work now as everything is fitted in that area. I understand this would increase the distance the pedal would have to travel but a small 10-15% reduction in effort would be a worthwhile benefit.

Has anyone done this, or do you think this is possible? If so, what bore would you recommend and is there a part or donor vehicle that would provide this?

I see on the SNGB website that there are two slave cylinders on offer. C24170 (which is the one I have), and C24145 (which appears longer than the other one). There is no narrative about these and bore diameter is not given, but they are both listed as OK for 4.2 E Types. Any thoughts?

Many thanks. I love this forum and look forward to any input.

My best regards

Steve

[MarekH]

Dear Steve,

I have an a non standard clutch master fitted. There is plenty of choice for bore width for the master cylinder. I can't remember what I fitted now, but it was the next size along.

The slave length is related to the type of adjustment mechanism (hydrostatic clutch vs spring returned clutch) rather than to gearing. I suspect all of the slaves available will be the same bore as each other because of the choice you have with masters.

kind regards
Marek

[mgcjag]

Hi Steve..just off the top of my head the clutch master is 3/4 the slave is 7/8.......useing both of these on my C type build ....a friend doing the same build replaced the master with a 5/8... its now much easier to operate his clutch....but more pedal travel required.... so upping the diameter of the slave and leaving the master as is should have similar effect? ...but dont know if you can get a 1in slave to suite....will have a search..let me know if you find something i might try it..Steve
Edit...1in Slave https://rimmerbros.com/Item--i-GSY113
Couple of calculations..standard setup 7/8 slave 3/4 master..1.13 advantage
7/8 slave 5/8 master..1.44 advantage
1in slave 3/4 master..1.33 advantage
Thats if my calculations are ok

[PeterCrespin]

Hi, I have recently started my engine for the first time and bled the clutch. All good!

I've not had an E Type before but the clutch feels OK, but fairly heavy.
Steve

For reference is it a diaphragm or coil spring clutch?

Pete

[MarekH]

Your calculations aren't ok - on two levels.

Firstly they should be proportional to to radius squared, as it is the cross sectional area which determines the volume of fluid pumped per inch of pedal stroke.

Secondly, you'll then need to divide one ratio by the other to determine the he percentage change in pedal stroke - knowing "1.13" on its own is meaningless until it is compared to another number.

Accordingly, changing from 7/8"-3/4" to 7/8"-5/8" gives 44% more stroke and .
changing 7/8"-3/4" to 1"-3/4" gives 31% more stroke than the 7/8"-3/4" did.

Bear in mind that this moves the clutch bite point further down the pedal stroke and you have to have enough spare "pedal travel" on top of that to accommodate the clutch plate and release bearing wear over time.

kind regards
Marek

[Steve1967]

Thank you, Steve, Pete and Marek for your replies, that is really useful information and very much appreciated.

I think I will order the 1" slave as its only £20ish (about a quarter of the SNGB price !!!) so its worth a try. Marek, does the fact that the pedal would have 31% more stroke mean that I could expect it to be 31% lighter? I would imagine it does?

I was concerned about someone elses thread on here about the proximity of the clutch fork lever when actuated to the back(front?) of the gearbox. Mine is quite close but as it works and seems OK I am not going to take the engine out just to put the deeper thrust bearing on it and yes, I did have my flywheel ground flat as some PO had had a go with an angle grinder on it!! With the mileage I am expecting to do, (maybe 3-4k per annum or so), it should last me a good few years before I need to have another play!

Of course while the pedal travel may be increased by 31%, the fork will move no more than it did so none of the above is relevant really.

I hope that all makes sense? I will order the part from Rimmers today and report back in a week or so how the clutch feels.

Thank you all again for your input.

Steve

[Steve1967]

Sorry Steve, I meant to add, I have fitted a diaphragm clutch.

Regards

Steve

[MarekH]

Yes, sort of. The bit where you take up the slack is no different as no fluid is being pushed against a spring.

You've then identified that the clutch rod has to move the same distance to disengage the clutch, i.e. the same work is being done and for that you have 30% more mechanical advantage so that bit is 30% easier.

That is then ameliorated or not depending on long your legs are as pushing that last bit with a nearly straight leg will feel easier than if your left leg is always close to 90'. This last is relevant because a lot of etype faults come down to the fact that the test driver was a little imp of a man and the average owner in 2020 doesn't remotely actually fit the car he helped design.

kind regards
Marek

[rfs1957]

S1 Seats, Pedal-Positions, Leg-Room, Comfort - an alternative approach ?

viewtopic.php?f=9&t=6023&p=42610&hilit=pedals#p42610

In this post (I am currently re-instating the photo-links) I addressed the issue of getting bigger/taller frames into the E-Type, and specifically how to tweak the clutch hydraulic ratio, or "gearing" as our friend calls it here, in order to reduce the travel when seeking to advance the pedals into the footwell, for longer legs.

I've not managed to reduce the post to 1% of its original length, but then nobody is obliged to read it.

With the spring clutch I had at the time, the clutch-pedal throw was too long and too flabby for my taste when fitted with the 7/8" slave, so - the very opposite of what's being mooted in this post - I went to a smaller 3/4" bore, with great success, to both stiffen the pedal and shorten the throw.

As my new engine will be now be driving a diaphragm clutch, it sounds like there may yet be surprises around the corner when I try to operate it with a 3/4" slave cylinder .......

Can anyone else offer comments about the differences in pedal effort between the spring and the diaphragm types.

[Steve1967]

Hi Rory, I've read elsewhere in the forum that a diaphragm clutch requires LESS effort than a spring clutch. This was part of the reason I fitted one.

I am becoming a bit concerned as I am not a weak person by any means and yet my clutch feels really quite heavy, which from you comments doesn't sound right. It is difficult to judge properly as I haven't put any seats in the car yet and I have nothing to push against. Which may be the difference?

I need to try someone elses E to be sure. Maybe someone at Stoneleigh this weekend will oblige?

'Regards

Steve

[MarkRado]

From experience: the diaphragm clutch has a in/out feel and is heavy at the point where it closes, so more difficult to dose (sorry for my English) than the spring clutch, which sems to have a constant backforce. But both not heavy at all compared to a 1974 Aston AMV8

[Woolfi]

"I wondered whether it would be possible to fit a slightly larger diameter slave cylinder to improve the hydraulic gearing giving a lighter pedal? I would rather not mess with the master cylinder as thats a lot of work now as everything is fitted in that area. I understand this would increase the distance the pedal would have to travel but a small 10-15% reduction in effort would be a worthwhile benefit.
Has anyone done this, or do you think this is possible? If so, what bore would you recommend and is there a part or donor vehicle that would provide this?"

I have done it succesfully. Roundabout 10 years ago the leg-power I needed, to press to clutch-pedal to the floor, was so high, that I started to avoid to drive in the city.
I have mounted a clutch master, which was a "step" smaller. After this change, the power to press was much less and the clutch still separated well. I could switch to the backward-gear without a noisy greeting from the gearbox.
A car-machanic told me, that when the clutch is old and the clutch plate is thinner, the pedal-power is rising. I never understood why. Marek has to explaine us.
After I have mounted a new clutch and a new clutch plate, the power was again lower, BUT the whole pedal-moving was NOT enough to separate the clutch completely. I had problems to switch to first gear while standing.
Therefore I changed back to the original master. After this the power was higher but still comfartable, but the clutch seperated well.
Therefor my advise for your problem will be: buy a (cheap) clutch master one step smaler or a clutch slave one step bigger and mount it. I am shure , that the power will be lower and HOPE that the clutch will separate well.
If you will renew the whole clucth in the future, change also back the the original clutch cylinder.
Regards Wolfgang Gatza

[MarekH]

Woolfi,

Here is how it works:-



Put simply, with a worn clutch, both of the yellow levers start out in a more horizontal position on the diagram so you have to push further to make them vertical to disengage the pressure plate from the clutch. (Assume pushrod freeplay is always adjusted correctly because that's what the manual tells you to do so.) What you have said is that your yellowy levers were too horizontal and you couldn't push them vertical because your foot didn't push enough clutch fluid down the line on account of the master cylinder bore being too thin.

Also, if a clutch is getting progressively heavier ~3000miles after you swap out a new master cylinder, check out whether the pushrod isn't scraping against the cylinder bore as it nears the end of its travel as it may not be travelling sufficiently in a straight line (it travels in an arc), or more precisely, in a straight line that matches the bore.

The clutch plate is outside the gearbox so its only link to gear change grinding has to be a reference to switching to or from a gear on the mainshaft which sticks out of the front of the gearbox and that shaft presumably never stops turning if the clutch does not fully disengage.

kind regards
Marek

[MarekH]

Actually, it may simpler than that. You said you put a new pressure plate in. It may have had yellow bits which were simply at a different angle to that in the old one, or the leverage loss on one pressure plate may have been different to that in the other pressure plate. In the diagram, there looks to be about a 5:1 loss of leverage about the (light blue) diaphragm pivot - two different manufacturer's pressure plates may not be directly comparable.

Basically, it's a geometry problem.

kind regards
Marek

[mgcjag]

And also dont forget that as the clutch plate wears and moves the yellow parts more to the horizontal the release bearing will also wear...so canceling out to some extent the extra movement the release bearing would have to make to release the clutch.....Steve

[MarekH]

....... (Assume pushrod freeplay is always adjusted correctly because that's what the manual tells you to do so.).........

I think it's already in the analysis Steve.

kind regards
Marek

[Steve1967]

Hi Marek and Steve, thank you for your help so far. Just one more thing......I think I have a major problem here with my clutch. I have put it off but I think I need to take the lump back out.

I think my problem (a very, very heavy clutch) is that this lever is so far back that the efficiency of the mechanism is compromised as the lever has already passed its optimum fulcrum point before I activate it, as your diagram above shows. See pic below, this is at rest and not with the clutch pedal depressed.

I have driven the car a few hundred yards and the clutch works but it is a monster to use.

As I mentioned previously, I have had the flywheel skimmed with a new diaphram clutch and fitted a new thrust bearing. I see elsewhere that these can come in various castings, some giving more throw, in so doing essentially moving the clutch actuating lever back towards the engine allowing for more movement.

These are not my pictures but show what I mean.... Ignore the carbon but look at the housing.

Unfortunately, I don't have a photo of the bearing I put in, it is the standard part C235752 but I have read that the various versions all have this number.

I remember being concerned that the lever was to far towards the back of the aperture in the bell housing when I assembled it, but not knowing any differently thought this must be normal. I should have listened to my intuition!

I've nearly finished my restoration and am currently working on the trim, but as much as I dont want to, I think its an engine out job.

I guess I just wanted some confirmation that there's no work around as I am totally gutted with this realisation and very reluctant to go so far backwards.

Do you (or anyone else) have any nuggets of wisdom or expertise about this or can you confirm my diagnosis? Also, do you have any pointers in ordering the correct bearing?

Many thanks again for your advice.

Steve

[mgcjag]

Steve PM sent

[johnetype]

Steve,

You've got a set of challenges here;

You may have fitted a release bearing that isn't tall enough

Your ex Toyota Supra(?) gearbox will have needed a clutch plate with different splines to a Jaguar one(?) leading to mismatched clutch and pressure plates?

That looks like an overly beefy spring on the clutch slave cylinder

Others can comment how far back the release lever should be but you're welcome to compare with mine.

A mini USB camera off eBay will let you see inside to check on the release bearing height BTW.

John

[rfs1957]

Hi Steve,

Whilst it appears that your problems are well and truly "upstream" of the release bearing, I wonder if the earlier diagrams might not already be usefully modified to represent more accurately what is going on inside the clutch, ie "downstream" from the release bearing.







To my mind, the essential point to grasp here is that the actual sizes of the X-Y mechanical advantage within the clutch are orders of magnitude greater than the very small Z dimension that represents the disengagement travel necessary to free the plate from the flywheel.

Therefore wear on the plate and faces have virtually no effect on the effort felt at the pedal.

Your problem indeed seems to come from an activating fulcrum, upstream of the release bearing, where the mechanism has gone way past its point of maximum mechanical advantage.

In this context, the travel of the release bearing is much more significant in relation to the sizes of the "levers" that are in play, and upsetting the intended geometry by starting off in quite the wrong place will have a much greater effect on the effort required.

To my mind the clutches that feel nicest are the one where you are initially pre-maximum mechanical advantage as you begin to operate the clutch, the mechanical advantage then going through its sweet spot roughly mid-travel, to meet the maximum load of clutch disengagement.

I am sure car and clutch manufacturers have hundreds of curves plotting the interplay between pedal movement versus clutch master displacement, itself a complex interplay, then slave to thrust bearing displacement - the one you're apparently struggling with - followed by the internal leverages across the clutch diaphragm spring that eventually produce the clutch separation.

Unfortunately this all seems to point to an engine-out conclusion !

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