: LS7 clutch and flywheel for Gen CTS-V

06-13-12, 09:51 PM
I replaced my deteriorating CTS-V clutch with a Corvette LS7 clutch this past weekend.
I saw some posts on this forum that detailed some of the issues for this modifications so I thought I would try it. It went reasonably well.
The hardest part of the project (well maybe there were a couple of hardest parts) was removing the clutch housing. A couple of the bolts were difficult to reach and the cover would not clear the flywheel. No matter what I did, I could not find a way to remove the clutch cover. The ultimate solution was to remove the bolts from the pressure plate, allowing it to move back far enough that I could remove the 6 bolts that attached the flywheel to the drive shaft. Removing that last bolt was exciting because that flywheel and clutch are really heavy.
The new Corvette flywheel is much thinner, so re-installing the clutch cover over the new clutch and flywheel was not so bad.
So here are the benefits that I got from the new flywheel/clutch:
1. The new assembly was axially smaller, making it possible to re-assemble the clutch housing. I'm not sure how one would install the cover if the OEM flywheel was used for the replacement.
2. The vibration went away. For about a year I have been experiencing a vibration that got progressively worse. It was most pronounced between 2000 and 2500 rpm, but lately, the amplitude of the vibration had gotten really bad
3. The vibration was starting to affect my fuel consumption
I have about 95,000 miles on the car, so the clutch was probably reaching end of life. I took care of two birds.
Now I have a conventional clutch with a much lighter flywheel, so I expect to get more service from this one.
I did not do any quantitative comparisons of the acceleration, but it really feels much better when you jump on it. The flywheel is significantly lighter, so it is bound to be quicker.
I used the corvette slave cylinder. The difference in the thickness of the fly wheels is about 3/4" so the cadillac slave cylinder will not reach the tines on the pressure plate. The corvette slave cylinder is more than an inch taller (axially longer) than the cadillac, so that probably explains why the take up point on the clutch pedal is so much lower. It catches at about 1" off the floor. But is releases fine, so there is no problem with grinding the gears.
This was the first time I've used a proper transmission jack for installing a transmissions. It made the task a ton easier. I paid $140 at Harbor Freight. Worth twice the price. I've never had a transmission engage the clutch so easily. And the Tremec is a beast (for a manual).
The cadillac flywheel is kind of crazy. There is a regular flywheel with the starter ring gear that bolts to the drive shaft. Then they pancake a second flywheel on the back of the first one. There is some rubber between the two that absorbs torsional load variations. The clutch disk is simple. It has the usual splined receiver in the middle and a single (double-sided) friction disk. But there are no concentric springs in the middle section. I guess they use the rubber between the two flywheels for this purpose. While there is a hollow centering dowel that keeps the two flywheels concentric, the deterioration of the rubber between them led to horrible vibration. Instead of damping the vibration, this play between the two massive flywheels was amplifying the vibration. The vibration had gotten so bad that at 75 mph (that's legal now here in Texas), the inside rear view mirror had become useless - just a blur.
I have seen some posts on this forum that questioned whether the lighter corvette flywheel would affect driveability. I really can't tell any difference. My wife drives the car most of the time and she can't tell any difference either.
There are a couple of minor issues with the slave cylinder. The bleed valve is too short on the corvette cylinder. I just re-used the longer one from my old cylinder. And the hydraulic line does not exist the cylinder in the same location. But fortunately, there is a notch in the transmission in just the right place to allow you to route the tubing out of the clutch housing. The new tubing is longer than the old one, but you will need that extra length due to the different exit point. Not a big deal.
So if your V has more than 50,000 miles on it and there is a vibration between 70 and 80 mph in sixth gear, you probably need to change your flywheel. My recommendation is to go with the LS7 conversion (flywheel, clutch, pressure plate, and concentric release bearing (integrated slave cylinder and release bearing).
I took a few photos, so if anybody is interested, I will post them.
Thanks to the pioneers that figured this modification out and tried it. My experience was reasonably painless.

06-13-12, 10:05 PM
i don't recall anyone else complaining of that vibration, but I'm glad you solved your problem! The clutch engagement point on the LS7 setup seems to come up after a couple hundred miles of driving.