Heavy clutch

Talk about the E-Type Series 3
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jagwit
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#1 Heavy clutch

Post by jagwit » Mon Feb 27, 2017 5:48 pm

Any theories on why the clutch of a S3 manual would be very heavy?

I will soon be working on a car where the clutch is at least 3 times heavier than the clutch on my '00 Land Rover Discovery 2 V8. I don't recall the clutch on the OTS I owned being this heavy.
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 73 Jensen Interceptor Std, 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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MarekH
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#2 Re: Heavy clutch

Post by MarekH » Mon Feb 27, 2017 6:27 pm

Dear Philip,

You should rule out any mechanical problems prior to the hydraulic circuit first.

Put a nice long coil of tubing on the slave bleed nipple and check that the pedal is really easy to operate when there is no fluid to move. One problem I had with my auto to manual conversion was that the clutch pedal hole for the master piston clevis pin was just slightly offset. This was enough to make the pedal become progressively harder to push as the piston wasn't moving in a straight line down the master bore. It was very slightly scoring it and making the pedal hard to press. It wasn't noticable at first but started to manifest itself after about three thousand miles.

Once I got wise to this, I replaced the master, but with a smaller bore and made sure it was all lined up properly, i.e. such that the plunger in the master cylinder had the most straight line path to take and not at the edge of its arc, so to speak.

I have a very light pedal now with the bite point much further down the pedal. No problems with it so far, touch wood.

If that all checks out, I'd want to know that the slave isn't rusty. Usually the rusty sludge accumulates along the bottom of the slave bore.

If that checks out, then the next and last thing to check isn't going to nice, or easy.....

kind regards
Marek

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#3 Re: Heavy clutch

Post by jagwit » Mon Feb 27, 2017 6:45 pm

Thank you Marek! Was this offset in a horizontal plane or a vertical plane?

What was needed to get the alignment correct?
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 73 Jensen Interceptor Std, 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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MarekH
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#4 Re: Heavy clutch

Post by MarekH » Mon Feb 27, 2017 7:12 pm

This was an auto to manual conversion and would hopefully not be a factor for an oem manual car. The hole for the clevis pin was too far from the pedal pivot, so the swing of the pedal made the plunger travel in too much of an arc as it went in and out of the master. The fix was to put a washer under one bolt holding the clutch master cylinder, so the master would line up with the pedal - it wasn't practical to redrill the pedal.

I think you are looking for a mechanical problem somewhere, since the only other logical possibility is that someone has mismatched the master:slave bore ratio, in which case, it should always have had this problem, which you'd diagnose via a very early clutch bite point.

The standard clutch master is a Girling Land Rover part anyway and they all look the same, save for a bit of writing and maybe a lug that's missing on the Jag ones - it fouls the pipe joint iirc as I had to file my replacement down a bit when I changed the bore size.

kind regards
Marek

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#5 Re: Heavy clutch

Post by jagwit » Mon Feb 27, 2017 7:44 pm

Thanks again Marek. Its nice to be forewarned.

The primary aim of my work will be to get the car 100% operational and reliable. To that end the car will arrive with a pile of spares including a new clutch master and slave cylinder. I'll therefore be sure to check the alignment as I fit it.
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 73 Jensen Interceptor Std, 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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Woolfi
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#6 Re: Heavy clutch

Post by Woolfi » Wed Mar 01, 2017 4:06 pm

I had a similar problem. At the end of the life of the clutch plate, the power to press the pedal completely rose to a uncomfortable amount. I changed the clutch master to another, which had a piston with a smaler diameter. This worked.
After I had renewed the clutch plate, the amount of hydraulic was too small, to separate the clutch completely. I mounted again the old master cylinder and all worked fine.
An old clutch plate is causing a change of the geometry.
Regards Wolfgang Gatza

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MarekH
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#7 Re: Heavy clutch

Post by MarekH » Wed Mar 01, 2017 5:01 pm

That's a bit worrying for me then - I have a smaller diameter master cylinder currently fitted. Why would I not be able to adjust this out by changing the pushrod length, were it to be a problem with a thicker clutch plate?

Freedom for Tooting!

kind regards
Marek

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#8 Re: Heavy clutch

Post by jagwit » Wed Mar 01, 2017 5:09 pm

Woolfi wrote:I had a similar problem. At the end of the life of the clutch plate, the power to press the pedal completely rose to a uncomfortable amount. I changed the clutch master to another, which had a piston with a smaler diameter. This worked.
After I had renewed the clutch plate, the amount of hydraulic was too small, to separate the clutch completely. I mounted again the old master cylinder and all worked fine.
An old clutch plate is causing a change of the geometry.
Regards Wolfgang Gatza
Very interesting Wolfgang!!!

Surely then a worn clutch release bearing could also be the cause of a heavy clutch since that also changes the geometry? Perhaps this car's clutch feel is the combination of both being worn?
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 73 Jensen Interceptor Std, 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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Rustyred
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#9 Re: Heavy clutch

Post by Rustyred » Wed Mar 01, 2017 11:06 pm

Worn clutches do not change the geometry, as the pivot points are fixed, all they do is increase or decrease travel.
With what Wolfgang did, fitting a smaller bore Master will increase pressure going to the slave at the sacrifice of fluid travel, the opposite is true also. Larger bore, less pressure but more travel, the same is said if you change the bore sizes on the slave for the same effect.
Binding anywhere in the clutch will cause heaviness, and that can be from rust/corrosion around pressure plate pivots, throwout lever pivots points, throwout bearing guide and nose cone, rusty or gummy input shaft and clutch plate splines. (can also be accumulation of crud build up from oil leaks and grease + clutch dust)
Also to check pedal shafts and pushrods for bind.

Most clutch manufactures are striving for lightness whilst maintaining stronger spring pressures, by changing the pressure plate spring pivot points, Couple of well known ones have been doing this since late ninties, Making heavy duty clutches very light under foot.

John
Restoring 73 Series 3 2+2

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