Vibration in 2000-2500 rpm range

[adamj]

I've had this vibration that I can't seem to diagnose and get rid of.
It occurs at a very specific rpm range, from approximately 2000-2500.
Above and below this range, the vibration goes away. (i.e. I can rev out of it).

This happens while driving AND while stationary, in any gear, and in neutral.

A few things I've done I thought might solve this:
- new motor mounts
- new transmission mount
- harmonic balancer, new ac delco

Vehicle has become smoother with less vibration after these things, but that original feeling I was getting is still there.
It feels like it may be coming from the transmission.
I have a SM 465 and NP208 t case combo.

 

[Georgeb]

Does it do it with the clutch disengaged?

 

[bucket]

I'm thinking the flywheel may not have the proper balance. It's very possible if it's been replaced with a parts store flywheel.

 

[Georgeb]

I'm thinking the flywheel may not have the proper balance. It's very possible if it's been replaced with a parts store flywheel.

Thats where I was going too. Another thought would be a bad or missing pilot bearing in the end of the crank hence why I asked if it does it with the clutch disengaged.

 

[adamj]

I just confirmed, and it still makes the vibration with clutch disengaged.
What does that mean now?

 

[Georgeb]

I just confirmed, and it still makes the vibration with clutch disengaged.
What does that mean now?

Most likely not in the tranny.

 

[Georgeb]

Most likely not in the tranny.

Score one for Mr Obvious! Anyway, it is running on all cylinders and not developing a miss or somthing at those rpms right? I was wondering about the flywheel too.

 

[adamj]

The PO did say he replaced the clutch not too long ago, and with it, the flywheel. That could be it...

 

[adamj]

I'm thinking the flywheel may not have the proper balance. It's very possible if it's been replaced with a parts store flywheel.

What's wrong with a parts store flywheel? Why would they even make an imbalanced flywheel? If I do need to replace the flywheel, how do I know I'm putting the right one in?

 

[bucket]

What's wrong with a parts store flywheel? Why would they even make an imbalanced flywheel? If I do need to replace the flywheel, how do I know I'm putting the right one in?

Sometimes they are just very low quality and not correctly engineered. But often they are fine. Most of the time, people want to just replace them because it's easy. But I'd much rather just resurface a known good one, if it even needs it. Often the flywheel just needs hit with 80 grit on a sander, to help the new clutch bed in.

 

[adamj]

I'm bringing it in to a shop to confirm, but if it is a new flywheel that's needed, which one should I get?
How about this one by Luk: LFW103?
I don't see any AC Delco ones available...

 

[bucket]

Do you know for sure if the engine is still original?

 

[adamj]

Not the original engine, it is a remanufactured unit of the same kind (sb350 with TBI) that has around 40k on it.

George, what do you mean by "a bad or missing pilot bearing in the end of the crank"? Is that still a possibility, or related to what bucket is getting at now?

 

[Georgeb]

Not the original engine, it is a remanufactured unit of the same kind (sb350 with TBI) that has around 40k on it.

George, what do you mean by "a bad or missing pilot bearing in the end of the crank"? Is that still a possibility, or related to what bucket is getting at now?

There is supposed to be a bushing or bearing installed in the end of the crank that the nose of the transmission input shaft slides into. If it is bad or missing it could cause misalignment of the clutch. You will want to inspect it if you take the trans out to change the flywheel. There ar different kinds out there but it is my opinion that the brass or bronze ones are the best. Since your vibration is there with the clutch disenguaged its probably not the main issue.
How bad is this vibration? Fuzzy rearview bad or small parts vibrate a little bad?

 

[adamj]

More like fuzzy rear view.
Is the pilot bushing something to change out if I have to change my flywheel out anyways? As in, is that a wear item?