383 vibration issue

[AUTOHOLIC]

I bought a stroked 350 to a 383 from a guy that raced the new engine twice and then switched to an LS engine. The engine was built with good quality parts by a well respected shop.
The engine was installed and is still with my mechanic. It was running smooth but has suddenly developed a vibration that starts about 1250 rpms and gets worse and stays the same at about 2500 rpms. The engine is externally balanced and has a fluid balancer. My mechanic has removed the belts and run it to eliminate anything like pulleys and accessories causing the problem. He spoke with the shop that built the engine and has a complete file on his it and checked the position of the flywheel weight which is all correct. He plans to pull the trans and clutch tomorrow to see it it eliminates the vibration. Neither of us understand as it suddenly just started this.
Has anyone encountered this?

[roadpilot]

Well here goes the guess's.............
How bout the engine mount pad?
What kind of fuel pump are you running?
Fuel filter restricted?

More guess's later

[AUTOHOLIC]

It has new motor and trans mounts.
It has an electric fuel pump.
No fuel restrictions

[roadpilot]

Originally Posted by AUTOHOLIC

It has new motor and trans mounts.
It has an electric fuel pump.
No fuel restrictions

Do you still run the factory fuel filter? I just changed mine and
it was almost closed off. I run a electric pump too and never thought
about the Orginal fuel filter.

[roadpilot]

Originally Posted by roadpilot

Well here goes the guess's.............
How bout the engine mount pad?
What kind of fuel pump are you running?
Fuel filter restricted?

More guess's later

The flywheel is balanced? Installed correctly?

[GTOguy]

Since it was running smoothly and suddenly developed a problem, something changed. Not likely an engine internal issue if it still runs fine with no noises. Possible clutch/pressure plate issue or defective or shifted motor or trans mounts. Also, verify the exhaust is not contacting the frame.

[AUTOHOLIC]

We found the problem.
The new clutch has a loose finger on it and have a replacement coming.
Thanks to all for your help.

[SJW]

Good of you to post a follow-up with the culprit identified.

Live well,

SJW

[AUTOHOLIC]

Originally Posted by SJW

Good of you to post a follow-up with the culprit identified.

Live well,

SJW

It is oh so important for people to post follow-ups as that is what really makes these forums so helpful to others later on that are searching for potential help with a like type problem.

[SJW]

Did you happen to take photos of that defective PP? I'm curious as to what it might look like.

Live well,

SJW

[AUTOHOLIC]

Originally Posted by SJW

Did you happen to take photos of that defective PP? I'm curious as to what it might look like.

Live well,

SJW

No, sorry I did not.

On another note, it still had a slight vibration that we just discovered the trans that was just rebuilt and has a new internal shaft that was bought from Tremac is out of spec. They said it was US made but my mechanic questions that and is so sick of getting junk NEW parts is looking for a quality USED part to replace it with. I too am sick of this and am dying to get my car back out of the shop.