One major problem I ran into is flywheel imbalance. I replaced the clutch and flywheel on my 460/ZF F250 two months ago. Ordered a Luk flywheel (along with the clutch) from a very popular online parts distributor. On start up, the thing blurred my eyeballs. I double-checked the application (correct). Removed the trans, clutch and flywheel, bolted the old flywheel back on, slid the trans forward without the clutch, bolted the starter on and started it up. Smooth as silk.
-Ordered a flywheel from the local parts store and returned the Luk. On assembly no vibration.
-Fast forward to last week. Ordered another Luk flywheel and clutch from the same distributor. Installed the flywheel, slid the trans forward, stabbed two bolts in, mounted the starter and fired it up. Although it was not as bad as the F250, definite vibration. Ordered a flywheel from the local store, yada yada. New flywheel fixed it.
-Now, before you say "Misfire!", realize I was a factory Ford tech since 1986. I've diagnosed and replaced a ton of slipped balancers on 5.0's, 3.8's etc. I *know* what engine imbalance feels like.
And the reason I mention all this: I believe parts manufactures have a responsibility to produce parts of reasonable quality. For me to get two imbalanced flywheels consecutively from the same company, with wildly differing applications, indicates a serious lack of quality control at Luk. They need to fix this. Once they do, they can feel free to comment here and I'll resume buying their parts. -Nuff said.