Nationals 2008. Heartland Park Topeka. Day two, run two. Car launched fine and was handling great for the first right hander into the long straight down the hill. Once the cam got into its sweet spot the revs climbed quick and at the end of the straight I heard strange sounds from the gearbox. The car was a bit twitchy in the hard right hander but accelerated fine through the walled offsets. I finished the run at about 80% not knowing exactly what broke. After the finish I called to my co-driver for a push, the car would not go back into gear and was done for the week (well, the week was almost over anyway we were the last heat).
After the dust settled we opened the hood and noticed that the transmission bellhousing was swiss cheese. The picture at the top of the page was taken at that time. I guess all that noise I heard was metal parts exiting the cast aluminum bellhousing. After thrashing on the car for two weeks prior to Nationals I was physically and emotionally done and let the car sit in my garage untouched for almost two months...
After my first run on day 2 of Nationals I had trouble getting the car back into gear after the finish. Wanting to complete the event in my own car I adjusted the clutch throw at the master cylinder just a bit and was able to get the car to shift again. Probably not the best "fix" in hindsight but sometimes you do what you gotta do in the heat of battle. My co-driver went out on his next run and did not have any issues shifting and nothing broke. I wasn't so lucky.
My initial theory after the failure was that this clutch adjusment triage caused the throwout bearing to ride on the clutch even when the clutch was clamped tight by the pressure plate. I assumed that the throwout bearing disintegrated at around 6000rpm on my ill-fated run. Other folks were not convinced and some thought that the M12 flywheel bolts had backed out (which has happened on this car in the past).
After removing the transmission I was actually surprised to see the throwout bearing intact and still attached to the collar in the bellhousing. What I was not expecting to see was the carnage that used to be my pressure plate. One of the spring levers (not sure what they're called) that is integral to the clutch operation had lost a rivet. In addition to that two of the flywheel dowel pins were missing as were two of the pressure plate bolts. These are the pieces that destroyed the bellhousing but why?
I was hoping to get by without having to purchase a new flywheel but it looks like that's not going to be the case this time. As you can see from the pictures, several of the pressure plate bolts were ripped out of the bolt holes. Also notice that there's only one dowel pin. I never found the others. Once it's replaced it will be the third aluminum flywheel that's been in this car since I started seriously autocrossing it. This flywheel can probably be cleaned up and re-drilled by a competent machinist but I don't think I'll chance it, I'll save it as a spare though.
A full picture of the pressure plate as removed from the car and a close-up of the broken pressure plate spring rivet are below. Was this rivet the cause of the failure or just collateral damage? One thing you may notice on the pics below are the extra holes drilled into the mounting flange of the pressure plate (right side of the picture).
When assembling the car with the new motor earlier in the year I had the pressure plate and flywheel balanced at a machine shop. The machinist noted that the flywheel was almost perfect as it was but the pressure plate required a lot of work to balance. I'm wondering if this is clue. I had no clutch issues all year with many autocrosses and lots of dyno pulls during the year. No matter, I've decided to ditch the Nismo pressure plate and go with an ACT solid disc setup...
Several folks on Hybridz.org have had good experience with the ACT clutches so I decided to give them a try this time around. I wanted the same style of clutch that I've been running for years (solid puck) and ACT had what I needed. I considered going with the same puck clutch with a sprung hub but figured it was just more rotating mass and more little pieces to potentially fail. I've never had issues launching with the solid clutch either.
The overall fit-and-finish and build quality seems to be much better with the ACT clutch kit than the Nismo and Nissan Motorsports parts I have used in the past. Everything was included with the kit including a new throwout bearing. I got a new T.O. bearing sleave from MSA just to make sure I had all the right stuff. New Nissan flywheel bolts from eBay and some M8x16 class 12.9 pressure plate bolts from McMaster-Carr completed my "kit".
Installation of the new Fidanza flywheel and ACT clutch and pressure plate went very smoothly. Dowels had locktite applied and were pressed into the flywheel using a vise according to the instructions. Flywheel, clutch, and pressure plate surfaces were thoroughly cleaned with solvent before assembly. I added hardened flat washers under each flywheel bolt and they were all torqued to 100 ft/lbs.
Pressure plate bolts got lock washers and were torqued to 25 ft/lbs (with a small amount of locktite). In the past I've used the factory recommended 17 ft/lbs on Nissan bolts in this application but I wanted a little more piece of mind this time and the 12.9 bolts could take it. Didn't want to go any more than that since I was threading into aluminum. YMMV.
And, here's the finished product. Of course since I've had issues in the past I'll probably pull the tranny after the season and double-check everything. Safety first!