Source for Clutch Master Cylinders?

[Igor+]

Could you advice me where can I buy GIRLING 0.625" (instead of standard 0.75") clutch master cylinder with integrated reservoir in London, UK area or on-line, please?

[davefiddes]

I bought mine from Demon Tweeks (www.demon-tweeks.com/). I believe they usually carry stock and ship pretty much anywhere.

Definitely a good idea moving to the 5/8" master cylinder. I did this a month or so back and it's made a huge difference to the drivability of the car. I spent quite a while making sure that the travel and orientation of the pedal was OK for the greater travel but having done that the clutch is much lighter and has more than enough travel to disengage properly. It is now possible to drive smoothly round town and shifts are much quicker on the move.

[ultimacz]

I was already looking for ways to make the clutch lighter, but it was always explained to me that 1. in a sportscar like this it should be tough, and 2. there is anyway no way to make it lighter. Great to hear there is a way, I still feel my left leg after driving 20 min. in slow traffic some days ago!

Could you please answer some questions:
- is it a direct replacement for the GTR, or does it need some customising (new brackets, welding,...)
- what are the costs
- any disadvantages or risks
- why does the factory not use it right away as a standard if it is better

Thank you,
Peter

[davefiddes]

Hi,

ultimacz said:

- is it a direct replacement for the GTR, or does it need some customising (new brackets, welding,...)

Yes it's a straight replacement part. You need to make sure you get the 5/8"(0.625") master cylinder with integrated fluid reservoir but other than that there's no problems. Just bolt it in and re-bleed the clutch circuit.

ultimacz said:

- what are the costs

38GBP plus VAT plus shipping

ultimacz said:

- any disadvantages or risks

I found I had to play with the adjustment of the throw of the pedal a bit to ensure that I had enough travel to fully disengage the clutch. I had also done a bit of work to the opening in the back of the pedal to stop the clevis fouling on the pedal (I bent my original clutch master cylinder connecting rod because of this).

Another disadvantage is that the pedal throw is greater. I've not found this to be a problem with making quick gear changes. As the pedal is much lighter it is possible to push it more accurately and smoothly. This seems to make up for the fact you have to move you foot more. I've not had it on a race track with the new clutch but George Ross has a similar set up and hasn't had any issues I don't think.

ultimacz said:

- why does the factory not use it right away as a standard if it is better

Don't know. Maybe the 3/4" master cylinder matches the older Porsche clutch/clutch slave cylinder better?

My 964 clutch/gearbox was very easy to overtravel such that the bolts on the clutch cover impacted the release fork with a 3/4" master cylinder. The 5/8" master cylinder seems to have just the correct throw required at the clutch. YMMV.

hope this helps,

Dave

[gdr]

Agree with everything Dave says. I think the clutch arm contact with bolts on cover with the 3/4" master cyl may be a result of using the middle pivot hole for pedals. I certainly prefer the lighter clutch with the 5/8" cyl and absolutely no problems in this area on road or track. Very easy and cheap mod, no problems reverting to original if you prefer the shorter and heavier pedal.

[GTRMikie]

I have also done this mod and agree with all that has been said. My 0.625 master cylinder came with a slightly shorter push rod than the one fitted to the 0.75 so I changed them over before fitting the new cylinder.

[gdr]

Worth noting that longer pushrods are available for the Girling Master cylinders. I got a couple from Merlin Motorsport for brakes as there was almost no thread engaged in balance bar when middle pivot hole used.

[ultimacz]

Thank you for all the good info. Will definitely try the lighter clutch.
This forum is a great source of information!