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Spec stage 2 clutch kit

Lightweight aluminium flywheel with steel insert
Worn slave cylinder

At 110k miles (178 000 km), the car had developed the "clutch pedal stuck to floor"  issue when shifting at high RPMs. This is caused by a worn slave cylinder, where 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. A sure sign of this happening is that the clutch fluid gets discolored again quickly after a change.

State of stock clutch

The OEM clutch from LUK is more than capable of handling the LS6 stock power. 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. 

However, with everything else disassembled, it would be dumb not to replace the clutch now, as it will probably not last another 20 years.

Guess what happens when a flywheel, a pressure plate and a clutch disk bounce around in a box across the Atlantic Ocean?

I purchased a new LUK OEM clutch kit from Summit Racing. The clutch kits from LUK are sent in a cardboard box without any protection and everything inside is free to bounce around. Across the Atlantic Ocean, this is bound to go wrong. Nobody would cover the damage, as I used a forwarding courier to send the kit from the USA to Norway. Summit Racing also refused to send or sell me a new clutch disk. Sold separately it has the same price as a complete kit. Not the best customer service by Summit Racing, I have to say.

I had to purchase a second clutch kit! 😒

Spec Stage II clutch kit

"Insanity is doing the same thing over and over again and expecting different results", so I did not order another clutch kit from Summit Racing. 

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 10.6 lbs. (4.8 Kg). 

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 the car wheel, you can bring the lighter bicycle wheel up to speed with less force and in less time than the car wheel.

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 possibly be a factor in the "clutch pedal stuck to floor" issue, so I'm happy without it.

Installing the new clutch kit

Prior to installing the new clutch kit, I made sure to fix all oil leaks at the rear of the engine
New flywheel installed. With ARP flywheel bolts and very tight tolerances, I had to carefully clean the bolt holes in the flywheel and every mating surfaces using a Scotch-Brite pad. The flywheel bolts are torqued to 75 ft lbs. (102 Nm) and secured with red Loctite.

Clutch kit balancing

If you've noticed the holes drilled in the flywheel and clutch cover, this is the work of Cylmo AS as they balanced the parts. The flywheel and clutch cover had a total imbalance of 4.2 ounce (120 g). For reference, a wheel with an imbalance of only 0.7 ounce (20 g) 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 0.14 ounce (4 g)

New pressure place and clutch disk in place. I'm using the propeller shaft to center the clutch disk, as this obviously has tighter tolerances than the plastic fantastic tool that is included with the clutch kit.

At this stage, I've only tightened the bolts enough to seat the pressure plate, I'll apply Loctite and tighten the bolts to final torque after having mounted the torque tube. This leaves the option to release the clutch disk if one can't get the pilot bearing/clutch disk/propeller shaft to line up when mounting the torque tube.