Vibration at 2100-2300 rpm

I'm having a hard time tracking down this vibration I have and I need some help. I know vibrations and rattles are typical in our cars, but this one is odd in that it appeared one day and has remained ever since.

It starts to develop around 2100 rpm consistently (and stays to only 2300, so it is a narrow range), but it often takes a few seconds to develop once that rpm is reached. Once there though, it stays. It is most prominent in D (3rd) and comes in the form of a cycle, changing approximately once a second (pulsating?) - that is, it is strong, then weak, then strong, etc... Sort of like a VVVVVVVvvvvvvvvVVVVVVVVvvvvvvvv pattern, where the big V is where it is strong for a second, and the small v where it is less strong. Occassionally, on certain days, it is much more powerful, rattling the entire dash and console (trans cover) - this happens only 1% of the time though. It is not as prevalent in any other gear or RPM range (and not under WOT at all).

It didn't develop after any specific mod. It simply appeared about 1.5 years ago and has remained ever since. But it has been there through 2 TCs (higher stall each time) and two UD pullies.

I am kind of puzzled right now. It is a narrow rpm band and has a specific light-heavy vibration pattern. It hasn't affected performance, and hasn't gotten any worse over the last 8K kms, but it is definitely not right still.

Any thoughts what may be the source of it?

I am havingg the same sort of harmonic vibration, but at 1200 rpm (85-90 km/h) in 6th gear.

I wonder if it could be improperly balanced tires - have you remounted/rebalanced your tires lately?

I have checked the tires and they are definitely fine, having been rotated and balanced. I had it with my goodyears, and now with the nittos as well. I always associated tires with vibrations through the steering column... I feel nothing there. Also, I think that would be more prevalent at a specific speed, not rpm.

I'm trying to think whether it is driveline or engine related. ?

Originally posted by Camaro ChriSS
I have checked the tires and they are definitely fine, having been rotated and balanced. I had it with my goodyears, and now with the nittos as well. I always associated tires with vibrations through the steering column... I feel nothing there. Also, I think that would be more prevalent at a specific speed, not rpm.

I'm trying to think whether it is driveline or engine related. ?

is the vibration througout the car or felt more on the steering wheel? It could be your U-joint is gone. Mine is, and I have a similar vibration only it's more at 2800 on the downshift and if I hold it at that RPM I'll feel it througout the car.

Have you ever replaced the drive shaft? Or a U joint? Or lowered the rear end? An out of phase (angle) DS can do that. But if it's just RPM sensitive and it doesn't matter it you're rolling or in any particular gear or at any particular road-speed, then it will be caused by something forward of the trans. (Engine related) My .02

I heard that when we were in your car the other night. I just figured it was a normal driveline noise as the few 4th gens Ive driven have it as well. Shuans has it too. Just for the hell of it Id try turning the driveshaft over 90degrees. You have had the DS out before when you did your stall.... any chance it started then?
CoryM

Sandeep: nothing is felt thru the steering column at all.

Black Robe: I have had the DS out once for my Loop, but I was naturally careful to put it back the same way. 'Course, since I've had two TCs installed, that means my DS has been removed twice (by two seperate shops). But, the vibration started a year after one install, and a year prior to the other. So, the installation work seems unlikely to be the cause - I suspect I would have noticed the problem sooner.

Cory: I am fairly certain this is not fully normal. No one else with an LS1 seems to know what I am talking about, so it can't be TOO common. I haven't spoken with many LT1 guys yet, but no one here has mentioned it being common. And Shaun's car is so far from stock I don't even know if we can compare them! ;)

i can't say i have this problem so i don't think it is in all of our cars.

My car bangs and hops and bounces so much with the 500 # springs , I couldnt tell you if peices were falling off let alone a vibration !! :D

if its rpm related its probably a bad wire/plug/coil or weight flew off the flywheel :)