Clutch master cylinder question.

[Alex]

Heres a question that I've been considering.....
If I were to fit a Stag clutch master cylinder would that make the clutch lighter or heavier?
Would it increase or decrease pedal travel,I know the Stag master is a larger bore but whats the answer?

Nothing wrong with mine purely an enquiry.
Thanks
Alex

[willcolumbine]

If it's a larger bore the pedal stroke will be shortened.

[Alex]

willcolumbine wrote:

If it's a larger bore the pedal stroke will be shortened.

Ok....why?Would it not just move the biting point?
Would that make it lighter ?

[spunkymonkey]

Using a larger bore master will pump more fluid towards the slave for the same amount of pedal movement.  That means that the slave piston will move further for a given pedal movement and that the biting point will move higher (ie:away from the floor).  Because you're moving the clutch diaphragm spring the same amount using less pedal movement, it will make the pedal heavier ie: you'll have to press harder.

One thing to be wary of is that, if you go too large on the master, there's a risk of the slave travelling too far by the time the pedal hits the floor - it will certainly moe further than it has been up until the change.  Because the seal will be moving beyond the old wear point that's fairly likely to start a leak from the slave and it might (unlikely but possible depending on the exact design) move far enough for the piston to jamb or even damage the clutch diaphragm.  It will also increase the pressure on your crank thrust washers when the clutch is pressed - not usually a good plan with these engines!

[willcolumbine]

If you have a big master cylinder it pumps more volume of fluid for a given movement of the pedal. The slave can only move forward and take so much fluid so one you've moved enough to fill it the pedal stops.

The effect is that it would move the biting point up, reduce the pedal travel and make the pedal harder to press!

[willcolumbine]

2047 wrote:

Because the seal will be moving beyond the old wear point that's fairly likely to start a leak from the slave and it might (unlikely but possible depending on the exact design) move far enough for the piston to jamb or even damage the clutch diaphragm.

The piston can't actually pop out and touch the clutch because it's travel is limited by the circlip on the end and besides, it's too far off to the left anyway!

[spunkymonkey]

Like I said, it's unlikely but circlips have been known to pop out of their grooves - the clip is only designed as a retainer in normal use, not a stop against hydraulic pressure.  

In fact, in a properly set up system, the piston should never contact the clip.  If the master gives extra stroke and you just floor the pedal on a fast change it can pop the clip quite easily as a fast-moving piston with maybe 30 or 40 lbf behind it hammers into a circlip in an alloy cylinder bore!  

It's also not the slave itself that can damage the clutch, but the release bearing pushing the diaphragm further than it should.  Won't cause an instant failure but can damage the diaphragm spring over time.