Lightweight aluminium flywheel with steel insert
Worn slave cylinder
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEifgC52Vw9IzD_VcM51QBCuRxqmTl3JmtoWEZiapOPUxjMzn2fAKFya7dRmLMe4sV3CEJOceOvSKwa6fLG2PCRf299snXSWJSRaSe3WohYzcrIxUQc-AKygOmybFn9yQogsAX-zlmBS6xkHpdbQ0HfmeoOLmCc6c_Jk-CBvv2hoB8fo34nhfF61TwPjzLs/w640-h480-rw/slavecyl.jpg)
At 110k miles (178 000 km), my C5Z had the infamous "clutch pedal stuck to floor" issue when shifting gear at high RPMs. Based on the pictures above, the blame is on the slave cylinder. It is a wonder it works at all, the clearly worn seals allows dust to enter the circuit and cause the slave cylinder to get stuck by the high inertial forces and the increased friction. Without disassembly, a sure sign of this issue is that the clutch fluid gets discolored again quickly after a change.
State of stock clutch
The car still had the stock clutch, which was in a surprisingly good state for the milage. Minimal surface wear and only a few small hotspots, one could even mistake the clutch disk for a new item. So the OEM clutch from LUK is more than capable of handling the LS6 stock power. However, with everything else disassembled, it would be dumb not to replace the clutch now, as it will probably not last another 20 years.
Spec Stage 2 clutch kit
I had originally purchased a LUK OEM clutch kit from Summit Racing which, unfortunately, was damaged on its way to Norway (link). It took infinite time to try and get that resolved, and in the end I simply had to purchase yet another clutch kit. I was lucky to source a lightly used Spec stage 2 clutch kit from a nice fellow in Alabama, who sent the parts to Norway in a box as secure as Fort Knox. This kit included a lightweight aluminum flywheel. The total weight saving is 4.8 Kg (10.6 lbs).
Less rotating mass is free power to the wheels, as there is less mass to accelerate for the engine. For reference, try to spin the wheel on your bicycle vs a car wheel, you can bring the lighter bicycle wheel up to speed with less force and in less time than the heavy car wheel - the engine will feel the same with a lighter flywheel.
The Spec clutch has a higher clamping force and torque rating than the LUK clutch, but it does not have the self adjusting pressure plate (SAIC). This mechanism is prone to failing, and could also be a factor in the "clutch pedal stuck to floor" issue, so I'm ok without it.
Installing the new clutch kit
Clutch balancing
If you notice the holes drilled in the flywheel and clutch cover pictured above, this is the work of Cylmo AS as they balanced the parts. The flywheel and clutch cover had a total imbalance of 120g (4.2 ounce)! For reference, a wheel with an imbalance of only 20g (0.7 ounce) is quite noticeable. Imagine a clutch spinning at 6000 rpm with an imbalance of 6 times that!After balancing, the imbalance was reduced to a total of only 4 g (0.14 ounce)
...TO BE CONTINUED.