K5 VIBRATION HELP NEEDED!

[Wardog]

Hello, I'm having difficulties isolating vibrations in my 75 K5 (350/350/203) that seems to start about 2.5K rpm and resonates till about 3K.  It has existed since I first bought it and appears more to do with engine speed rather than vehicle speed (it vibrates any gear or range).  It motor appears to have been rebuilt recently before I acquired it.  I’ve replaced/repaired the alternator, waterpump, harmonic balancer, front/rear driveshafts, motor mounts, timing chain, pulleys, fan, transfer case, and probably other things that escape me.  I temporarily installed a set of part time hubs and removed the front driveshaft to isolate the front axle but the vibration still existed.  Is it possible an unbalanced reciprocating assembly could cause this?  Any help or ideas would be appreciated.
Thx in advance/Mark!

[Blazin]

Did some halfwit put a 400 flex plate in it?
 My buddy has a 64 Panel delivery with a 283 / TH350, the motor ran great but seemed to have a visible shake when idling. It also had a resonate vibration all through the the truck from about 2500 RPM to about 3500 RPM was the worst. Some mouth breather had put a 400 flex plate in it. Swapped it for one off a 350 I had and it completely went away.

[VileZambonie]

Can you feel the vibration without the engine under load?

[Wardog]

Thx for the quick replies.  Best I can tell the flexplate is for a 350.  I was thinking along the lines of it being a 383 with a 350 balancer/flexplate, not sure how that would act.  I haven't noticed it when I run it up in park, I'll try that tomorrow.

[Wardog]

I run the motor up to to  over 3.5K while in park, there was a definite vibration that seemed to start right at 2K and continue on till I got out of it.  The vibration was constant, much like a an out of balance fan whereas when in gear it is more of a pulsing vibration.

[Josh454]

Take the belts off, take the bolts out for the torque converter and see if it pesists.  If it does it's going to be internal to the engine.  Just make sure the converter is back all the way or it can weld its self to the crank.  And obviously you can't run it long without a water pump.

Is the exhaust grounding out anywhere?

[VileZambonie]

Josh454 took the words out of my mouth... Let us know what happens.

[Wardog]

I'll get on that this weekend.  The exhaust is fairly new and doesn't hit anything.
Thx

[Wardog]

OK- I run it up without the belts-still vibrates.  I unbolted the torque converter and hand spun it around-found that every third or forth revolution I noticed a metal "ting".  I suspect it is something inside the tranny pump, looks like the tranny'll be coming out.  I have a TH400/203 combo that was destined for another project that may be redirected.

[SUX2BU99]

I have a pulsating vibration around 2100 RPM that's there in park, driving, wherever. Once the TC is unbolted does it just slide back? How far?