I've always had an rpm dependent vibration from the engine that was most noticable around 2,300 rpm. I always thought that it was my flywheel, but i just swaped in a T56 with a new flywheel and the vibration is still there. Now that I have a poly-trans mount, the vibration is more noticable. The engine runs real strong and I think the motor mounts are ok because the engine doesn't "jump" when I rev it. Could my harmonic balancer be bad? Does this sound like a symptom of a bad balancer? What would I look for on the balancer? If the outter ring is not shifted in, does that mean it is ok? I don't want to waste money on a new balancer if that is not the problem.

thanks,
Chris

 

might be a miss, might be bad dampner, i'd suspect a miss before i would the dampner

 

I don't think that it is a miss. If it were a miss, wouldn't it idle rough, and have overall bad engine performance?

 

no you could have miss at any speed or rpm but not all the time, might idle fine and miss under load

 

Is your manual trans flywheel balanced for a one-piece rear main seal style crank?

 

The flywheel is a stock LT1 flywheel, which is balanced for a one-piece rms. I had the same vibration with my stock flywheel.
I still don't think it is a miss because the vibration is independant of load. The motor still pulls hard. The vibration seems greatest at about 2,300 rpms, then it comes back at 3,000 but to a lesser extent
I'm thinking of getting the Streetdampr fluid damper. Would this be a complete waste of money? I looked at my balancer and it didn't seem to wobble. I was hoping that the fluid damper would be able to absorb this extra vibration. What else could cause this vibration?...the crank?

 

I have a similar vibration. My engine is smooth when parked and I can rev it up while parked and it barely wiggles a glass of water, but as soon as it's under load and hits 2500rpm the inside of the car starts to shake and then it goes away around 3500rpm.

Does your car do the same thing? Is it smooth when not under load? Anyways, I'm going to change my u-joints because there's not much elses to do. I'm running a Fluidamper and it takes a bit of it, but not enough for me to stop worrying about it.

 

Cruz'N Bruz'R, my engine vibration is independent of load. It vibrates if I rev it in neutral, or any other driving condition when the engine is at 2,300 rpm.

 

I had the same problem; vibration independant of load. Switched from an auto to a T-5, & all the sudden it shakes so bad at 2000 RPM & up it felt like the knock sensor was fooled and it took out timing. I got the clutch/flywheel assembly match balanced (for $85), voila, no more vibration. It was 3 oz. (!!!) out of balance, by the way. Seesh.

What sucked is that it was a new $200 nodular flywheel and a $300 Dual Friction clutch; allegedly Centerforce balances everything before sending... Riiight. It was the clutch, too--I rev'ed the motor w/o clutch on it in the garage, and there was no vibration. So, the next clutch I get will need to be match balanced to the flywheel AGAIN, since know its off to compensate for the current imbalanced clutch. I love the way it works now, and the Dual Friction design is brilliant IMO, but what a pain!

If you haven't already done so, I'd recommend verifying the balance of these items first--just because its supposed to be okay doesn't mean it is, & truth is stranger than ficiton--maybe someone had a screwy balance job (like mine) or something on your LT1 flywheel.

Sorry about the venting, and I hope this helps.

 

hey chris - i have a 92 305 w/ 160k+ and had a vibration when sitting at idle. the tach would not move, the engine was amooth.

my dealer thought it may be a harmonic bal. however after inspection the motor mounts were bad. "metal to metal" he said.

new mounts, no vibration.