Wierd Vibes.....

[nismo_zt]

So, ive got a vibration, it is felt through the hole car pretty much, starts around 1800 rpm, then goes away through the 2k's, and then comes back and is a bit more intense right at 3k, from there on up, its above the resonating frequency, so its super smooth.

Heres the setup, s13 hatch with a built ka-t, and what ive done to try to figure it out since the problem started.......

Changed the entire motor, including block, pistons, rods, crank, harmonic balancer, turbo manifold

Changed the clutch, flywheel, transmission

Still have vibration

It seems less noticable when in neutral, and since its not speed related, only rpm related, i didn't think it could be the drive shaft or diff, but i have an aluminum DSS one piece and a s13 VLSD just for info.

any ideas? as a note, as i recall, it first started after a night of drifting, so i figured it was the old clutch somehow losing balance after an over-rev, but after changing the clutch, problem is still evident.

thanks-chris

[Tyrell Corporation]

Have you checked all your mounts?

[nismo_zt]

I put nismo motor and transmission mounts in with the new engine, and since then ive swapped another engine into the car, when i did it this last time, the mounts were firm. Ive heard, but not actually seen a "broken" one before. If they are bad, is it pretty obvious? if the car is idling and i grab the throttle body and rev it, there is very little engine movement.

[nismo_zt]

granted there is no real load on it at that point.

whats the best way to tell if the mounts are broken without taking them out?

[Tyrell Corporation]

Well, if they are dirty, sometimes you can visibly see a crack in the rubber...doesn't sound like mounts to me, after your reply. It was a shot in the dark, because there are plenty of possibilities.

Your description is a little vague in terms of the circumstances surrounding the problem.

You say this is most noticeable under driving conditions?

Through every gear, or mainly noticeable in high gears?

What is the extent of the vibration level? Mild, high frequency vibration? Lower frequency rumbling? Loud? Quiet? Please elaborate.

Steering wheel shaking visibly?

Could be something as simple as your wheels becoming unbalanced.

[nismo_zt]

The vibes are most noticable under load, light to medium acceleration, and are also most prevalent in lower gears, 1,2,3. There is no steering wheel vibration, nor can i feel anything evident through the gas/brake/clutch pedals, and the level seems to be mid to high frequency, not low and rumbling.

It's kinda like driving over a rumble strip on the interstate, but maybe only about 25% as intense.

[Tyrell Corporation]

You just shot down the possibilities I was thinking of...

Hmmm... in a hurry, off to work. I'll post this afternoon, this sounds strange.
Modified by Tyrell Corporation at 10:56 AM 5/1/2008

[Tyrell Corporation]

I have thought about this for a while, and this type of diagnosis-over-the-internet just doesn't seem possible.

From everything you have described, I am inclined to think that the engine isn't balanced. But, at the same time, I don't think that type of diagnosis should be given over the internet.

So, I'm going with, "Sorry, I can't help you.".

Have you really replaced all those parts, specifically with the intention of ridding your car of the vibration?