Clutch Master Cylinder

[bluesatin]

Thinking of changing this to a different size. Any feedback from anybody who has fitted one would help as would the best size.

[Pb3]

Have you done a search, this topic was discussed a long time back. I seem to remember the issue can be with pedal travel when changing the bore size. Has anyone ever fitted a servo to the clutch system?

[bluesatin]

I did a search and it was Wayne that did this. He mentions the standard master cylinder bore as 3/4 (19.1mm) and has gone to 5/8 (15.9mm). I wonder what others have done as you can also get 7/10 (17.8mm) which looks like an ideal halfway which would reduce some of the pressure without reducing the travel of the slave that much.

[davefiddes]

I found that the 5/8" cylinder eliminated the clutch over travel I was experiencing with the original 3/4" without increasing the throw of the pedal unduly. Perhaps with a different gearbox and/or better set up pedal this might not be necessary. I do find the lighter pedal makes all the difference when driving in heavy traffic but doesn't seem to slow up the speed of my gear changes (reducing the weight of the gearchange lever would make them quicker for sure).

[martinlaw]

Dave,

Which gearbgox are you using?

l am using a Getrag and find the pedal rather heavy.

Where did you buy the 5/8 master from?

Cheers,
Martin.

[shithotfast]

I changed mine (get it from Ultima or DTweeks...) to a 5/8ths. Travel was less (which is fine) so changes are faster and clutch (twin plate TILTON) is much lighter to use. You can always go back.... but I found it a great mod.

[GTRMikie]

shithotfast said:

I changed mine (get it from Ultima or DTweeks...) to a 5/8ths. Travel was less (which is fine)

Are you sure Paul?

Surely if the cylinder has a smaller diameter, then the pedal has to travel further to shift the same volume of fluid as the larger cylinder, albeit with less effort. (I too have done this mod and recommend it)

[pilbeam_mp62]

I e-mailed the factory in September and asked the following :-

"I believe that the standard clutch master cylinder that you supply is 3/4" (?)

Would it be possible (and hopefully, you do not think this is a bad idea..) to supply
me with a 5/8" master cylinder instead, for a slightly "lighter" clutch pedal feel ?".....

.....This is the reply I got from Richard:-

"Kelvin,

This wouldn't be a good idea as it can cause clutch clearance issues, therefore we only supply 3/4"
Best Regards
Richard"

I personally don't understand the technicalities, I am just letting you know what my reply was.

Regards
Kelvin

[davefiddes]

martinlaw said:

Dave,
Which gearbox are you using?

I am using a Getrag and find the pedal rather heavy.

It's a G50/03 with the starter on the engine side. I believe that newer adapter plates put the starter on the gearbox side.

The Getrag sounds like it could be quite different. My main motivation for changing was that the slave was overtraveling the mechanism so that the flywheel bolts were hitting the release fork. If this isn't happening for you then having a smaller master cylinder may not give you enough throw to fully disengage the clutch.

martinlaw said:

Where did you buy the 5/8 master from?

Demon Tweeks though they seem to have put the price up. Car Builder Solutions seem to offer the same part for about the same money as I paid.

[shithotfast]

GTRMikie said:

shithotfast said:

I changed mine (get it from Ultima or DTweeks...) to a 5/8ths. Travel was less (which is fine)

Are you sure Paul?

Surely if the cylinder has a smaller diameter, then the pedal has to travel further to shift the same volume of fluid as the larger cylinder, albeit with less effort. (I too have done this mod and recommend it)

sorry... confusion... your right that the pedal has to travel further but I found that with my clutch the "standard" pedal travel was too much, i restricted how far the pedal travels now (I put a bolt on the chassis behind the pedal )...and works fine. Not sure if the 911 clutch needs more travel than this mod would allow...