Vibration at 3000 RPM

[JohnnyPopper]

1978 K-10, 350, 4BBL, TH350, NP203.

I toasted my original 350 last month, I have a used but fresh crate 350, had it installed by a local dismantle / repair shop.

Took delivery, ran fine, good power. Developed issues with the part time 4x4 conversion kit they installed.

Got that resolved, but on driving it home, realized a serious vibration at 3K RPM.

Figured the rear drive shaft had given up, had a new one built.

Same vibration.

Then I realized it's not the drive train- I get the same vibration in park, in Neutral, no connection to the drive train.

Now, I paid these guys good to do the original work, but their fixing the Transfer case was on them,  I have sneaking hunch there was some payback. Maybe I'm being paranoid...

So I will release tension on all the belts when she is cold, rev up to 3K to see if it still there, if it is not, I will look at each driven component.

If it is, I guess I can see if someone hung a weight on one of the 3 flex plate bolts.

I thought too that maybe the distributor might have moved.

Any other places to look?

Thanks in advance for your help.

 

[VileZambonie]

Although it sounds like you hired a knucklehead, I doubt they intentionally created a nuisance for you. After all, it would only cause you to go back and complain. Is the correct flexplate installed? What fan is on there? I agree, disconnect the drive belts and see what happens.

[JohnnyPopper]

Thanks VZ.

They're a pretty good outfit, have been doing this since '74. Move a lot of metal. I've bought many parts, but this is the first time I've used them to do work.

I agree the knuckle head Trans guy should have known more about the Miles Marker 501 he sold me. "metal spacers matter" 

My paranoia is that I bring it back and they say whatever they want and charge me to "fix it".

The motor came out of a 1980 C-10 that I'm going through right now. Flex plate is the one it came with.

And as I mentioned, when I first picked it up after the motor swap, there was no vibration at that RPM, just racking noise in the xfer case under load.

I'll get to the belt loosening and go from there. 

[bd]

Unless you're positive it's a mechanical out-of-balance issue, you may want to verify the firing order before tearing anything else apart.  Look deep inside the plug wire boots at both ends for evidence of soot or discoloration.  While you're at it, remove the distributor cap too and inspect for cracks or rotor damage in case the distributor kissed the firewall.

[Stewart G Griffin]

Just off hand things i'm shooting out:

Check the condition of the harmonic damper/balancer.  Did the shop use your original on the new crate?

Check the condition of the trans mount and engine mounts, even though you said vibration still happens in neutral/park.

[JohnnyPopper]

Thanks for the input Guys.

The motor is out of a 1980 I bought last summer, and ran fine.

They used the harmonic balancer that came with it.

I will check the wiring first.

[JohnnyPopper]

So I finally got time to investigate the mysterious vibration.

Figured I would take the advice to look for electrical problems first.

Picked up a new cap and rotor, upon inspection, the rotor was only tied down with one screw, and it was loose. Looking good...

Back together, started, still shaking at 3K rpm!

Slacked the two belts, no shake.

Looked closely at the fan mounting screws, and lo and behold! 2 were missing, the two remaining were opposite.

One of them was backed out about .5 inches, and the other was loose!

I had the engine swapped and for two weeks there was no vibration prior to me dropping it off.

They had to take the xfer case apart to install spacer bearing in the Miles Marker 501 kit they had failed to install  two weeks earlier.

Noticed the vibration the day I picked it up to take home.

Can people be that evil and petty?

That fan could have come loose and destroyed a good many things...

I think I will troll them on my next visit to buy used parts, and see who bites.

However, I'll keep in mind 'Vengeance is mine says Jehovah, I will repay'

Believe it or not, that Scripture has saved a lot of jerks without their knowing it...

Mystery solved, thanks again for your help!

[zieg85]

a mistake that should have been caught.  They probably removed the fan to tilt the trans assembly once they removed the cross member in order to not break the shroud or worse.

[VileZambonie]

Sounds like they just didn't properly tighten down the bolts/nuts. They need to be tightened incrementally opposing and thread locker is a good idea. Mechanical fans are a lot of weight, I highly doubt there was any malice, just a mistake or incompetence.