OK. I need some help / advice pretty please. I just recently purchased my first ever vette back in December. I have not had many opportunities to drive it as the weather here in Indiana has not been favorable. But I did get to take it out Saturday. The car has a high frequency vibration that is engine RPM dependent that does not feel “right” to me. I feel it clutch in or clutch out, sitting in the driveway free revving the engine. Under heavy acceleration in 3rd gear the shifter rattles pretty noisily. My first thought about the vibration was something is out of balance. I can feel it in the shifter and if I place my foot lightly on the clutch pedal I can feel it there. The vibration gets more pronounced as the engine RPM’s climb. I purchased the car as is, the motor work was already done by the previous owner(s): SDPC built the forged 402 shortblock, Vette Doctors assembled the long block and installed the motor. The build sheet for the short block simply says it is “balanced & blue printed”. I am going to assume that this means the rotating assembly is zero balanced. The car also has a Spec Stage 3+ clutch and Spec aluminum flywheel. I have read few threads where folks have had to “match balance” their new clutches to there old stock clutches and flywheels – due to the stock units being “off-balanced”. Obviously my car is no longer stock, but as this is my first vette, I don’t know a lot about them. I was going to remove the Spec clutch and flywheel and have them checked for zero balance. Based on my description is this the correct thing to do to try and eliminate this vibration I have?? Do the front of these motors have a harmonic balancer on them that is “off balanced”?? If so, then maybe my Spec stuff is zero balanced and is throwing everything off?? This is where I need help. I was also thinking about replacing the Spec clutch and flywheel as I don’t really like it, the car is not a race car, doesn’t go to the drag strip is just a weekend and nice day toy, and the spec stuff is not “as drivable” as I would like. If I replace it, should I get the new components zero balanced?? Could it possibly be a bad motor mount?? How would I go about checking that?? Any help would be greatly appreciated. This vibration is the only thing I don’t really like about the car. Thanks in advance!!

Steve

 

I would peek at the harmonic balancer when the motor is running, if there is excessive wobble that "might" cause this but your description seems to point more towards the clutch. While the winter is still upon us, you may want to first contact SDPC and talk to them about the short block. They are an excellent vendor and I am sure they will provide you with their assembly methods. Then give Vette Doctor's a shout and see how they handle the clutch balance when they do an installation. Once you have all of the information you can decide whether or not you want to pull the assembly. Once pulled, I would also check the torque tube bushings and other rotating parts that typically run into issues with higher hp applications.

 

Thank you sir. I did call SDPC and they do zero balance their short blocks. Now I just need to figure out what is apparently "off balance". Only three things that I can think of: flywheel, pressure plate/disk, or harmonic balancer on the front of the engine (if there is one - I dont know if it is actually a harmonic balancer or just a crank pulley).

And thanks for the heads up on the torque tube couplers, excellent idea. Very easy to replace those once the driveline is out of the car.

Would a bad motor mount cause a high frequency vibration that is engien RPM dependent?? Anyone now how to check for a "bad" motor mount? And can they be replaced with the engine in the car?

Thanks again for the help!

 

Highly likely its actually coming from your clutch assembly and its reasonably common to be very honest with you. The Vette's are very sensitive to clutch/pressure plate imbalance because it gets further amplified by the torque tube and prop shaft. I had a Spec in my car a long time ago that was out of balance by 36 grams (thats alot)....After welding a piece of mallery metal direct to the pressure plate (which was the culprit) and getting the balance much closer, the car felt smoother at RPM's and I had a lot less rattle and vibration in my shifter.

Its obviously a PITA to get to and check but the next time the driveline is out of the car I would send the clutch/flywheel assembly out to be balanced'.

Tony

 

Thank you Tony! This actually good to hear, because I was seriously considering replacing the spec clutch and aluminum flywheel anyway. I just dont like the way the clutch feels and the aluminum flywheel is a bit of a pain for a stop light to stop light, city car. The car isnt a drag car, just a weekend toy and I am thinking about going back to a stock steel flywheel to help driveability a bit. So this is a perfect excuse to spend more money. My wife will absolutely love to hear that!

Thanks again, I really do appreciate the insight!!

Steve

 

I got the spec 3+ and fidanza flywheel. to driving stop light to stop light with it. But it grabs crazy fast

 

let me know if you want to sell it cheap i will have it balanced

 

The flywheel adn clutch will be for sale in about a month.