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Author Topic: Size clutch master cilinder  (Read 4338 times)
Bart_Maztra
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« on: May 09, 2009, 09:17:08 pm »

I have renewed my clutch master cilinder. (in fact, carjoy did it)  After the job was done, the clutch pedal needed much more force. So i suspected the bore of the cilinder. The bigger the bore, more power is needed to apply the clutch pedal.  It turned out that a mastercilinder of a 2.2 was fitted. (my murena was a 1.6)

Then the cilinder is replaced by a smaller cilinder. The clutch pedal become much lighter, but stil not as light as it was.

My old master cilinder have a bore of 19mm, and the first new cilinder had 22mm.  The second new cilinder seems to have the same numbers written on it as the old one, alltough the old numbers are difficult to read.

So my gues is that i have now 20,5mm?

Carjoy don't seems to have 19mm cilinders.
Are there rebuild kits available?
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Jon Weywadt
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« Reply #1 on: May 09, 2009, 09:38:16 pm »

I have renewed my clutch master cilinder. (in fact, carjoy did it)  After the job was done, the clutch pedal needed much more force. So i suspected the bore of the cilinder. The bigger the bore, more power is needed to apply the clutch pedal.  It turned out that a mastercilinder of a 2.2 was fitted. (my murena was a 1.6)

Then the cilinder is replaced by a smaller cilinder. The clutch pedal become much lighter, but stil not as light as it was.

My old master cilinder have a bore of 19mm, and the first new cilinder had 22mm.  The second new cilinder seems to have the same numbers written on it as the old one, alltough the old numbers are difficult to read.

So my gues is that i have now 20,5mm?

Carjoy don't seems to have 19mm cilinders.
Are there rebuild kits available?
That sounds strange. The bigger the bore of the clutch cylinder, the less power you should have to apply to the pedal, but at the same time, you have to press the pedal further down to get the same length of travel on the clutch cylinder. It is a matter of fluid dynamics. The piston in the cylinder on the pedal has the same diameter as before and pushes a certain volume of fluid for a given amount of pedal travel. When this volume of fluid goes into a larger diameter clutch cylinder it makes it travel a shorter distance than the same volume would in the smaller diameter on the original cylinder. But at the same time the pressure should be lower. The larger the diameter of a piston, the lower the pressure required to exert a given force. That is because the fluid has a larger area on which to press to generate the force.

I wonder if there might not have been, and perhaps still is, some obstruction in the fluid line.
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Matranaut par excellence Cool
Bart_Maztra
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« Reply #2 on: May 09, 2009, 10:02:06 pm »

Jon.
Your theory is true for a slave cylinder (mounted at the motor), but it is inverse for the master cylinder (mounted on the pedal).

My murena is from 1981. Maybe earlyer models have 19mm and later models bigger master cylinders?Huh
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Anders Dinsen
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« Reply #3 on: May 10, 2009, 08:56:17 am »

The spare parts catalogues list only one cylinder for the 1.6, but that doesn't mean that there could be another one available. What size is the Bagheera using? In any case, I recall having seen rebuild kits being available for the 1.6 master cylinder (Simon advertised them on his homepage at one point, but they aren't there now) - the problem has always been the 2.2 cylinder, for which rebuild kits only recently have become available.

/Anders
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'82 Murena 2.2 prep 142
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roy4matra
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« Reply #4 on: May 10, 2009, 02:09:39 pm »

I have renewed my clutch master cilinder. (in fact, carjoy did it)  After the job was done, the clutch pedal needed much more force. So i suspected the bore of the cilinder. The bigger the bore, more power is needed to apply the clutch pedal.  It turned out that a mastercilinder of a 2.2 was fitted. (my murena was a 1.6)

Then the cilinder is replaced by a smaller cilinder. The clutch pedal become much lighter, but stil not as light as it was.

My old master cilinder have a bore of 19mm, and the first new cilinder had 22mm.  The second new cilinder seems to have the same numbers written on it as the old one, alltough the old numbers are difficult to read.

So my gues is that i have now 20,5mm?

Carjoy don't seems to have 19mm cilinders.
Are there rebuild kits available?

The 1.6 clutch master cylinder should be 19mm bore and the 2.2 should have a 20.6 mm bore (note these are really imperial sizes 19mm = 3'4" and 20.6mm = 13/16") but I have found 2.2 master cylinders on a 1.6 before now, and it seems some people don't realise they should be different!

If you had a master cylinder with a 22mm bore as stated then it was entirely wrong!  Trying to move that much fluid would make the slave cylinder bottom much quicker and could account for the high pedal load.

If you put a 2.2 master cylinder on a 1.6 then the volume of fluid moved for the same pedal movement will be greater and try to force the slave cylinder further.

If the clutch is almost worn out it usually gets harder on the pedal, so increased pedal pressure can signify the clutch is near the end of its life.

The number cast onto the master cylinder will often be the same as they used the same casting and simply drilled them different sizes.

Simon stock 1.6 and 2.2 seal kits.  See their new Murena parts pages.

Roy
« Last Edit: May 13, 2009, 11:54:59 pm by roy4matra » Logged

Bart_Maztra
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« Reply #5 on: May 10, 2009, 07:45:39 pm »

Simon just emailed me that they have 1.6 seals on stock, and he confirmed they are 19mm.
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JV
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« Reply #6 on: May 11, 2009, 09:51:14 am »

If you had a master cylinder with a 22mm bore as stated then it was entirely wrong!  Trying to move that much fluid would make the slave cylinder bottom much quicker and could account for the high pedal load.

If you put a 2.2 master cylinder on a 1.6 then the volume of fluid moved for the same pedal movement will be greater and try to force the slave cylinder further.
Roy

22mm vs 19mm gives +34% fluid moving, 20,6mm vs 19mm gives +17,5%

Jan
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Jan Verdam
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