[taalltheway]

Hi,

my 467 with edelbrock heads and comp XE274 cam runs nicely from idle to about 3000 rpm. Beyond that its starts vibrating. Nothing crazy but very noticable. I can rev higher but the vibratioin is there. It does this while driving but also in neutral at a standstill so it is not in the drivetrain or chassis. Timing tops out at 30 degrees at about 3000 so it is even a little bit on the lower side.

Any ideas?

[FrankieT/A]

Auto or stick?

[David Jones]

How was it balanced when it was built?

[taalltheway]

It is an automatic. No idea how it was balanced since I bought it from somebody who built it. before tearing into the engine I would like to eliminate all other options first. Years ago I had a similar situation on a 73 Trans am. Turned out that the spark plug wires were old and sparks flew from cable to cable...but I guess I will not be that lucky this time...

[Navy Horn 16]

My $ would be on torque converter. I had a similar issue.

[Gary H]

Is it a vibration, or possibly a miss? Sometimes they feel the same

[Kenth]

Non-matching crank and flywheel?
Std crank with neutral flywheel or std flywheel with neutral crank.

[Joe's Garage]

I had a friend years ago whose recently-purchased Firebird developed a vibration that was similar to yours.

We decided it must be the torque convertor and put it up on four jackstands with the plan to take the convertor bolts out and push the convertor back and then start it up with the convertor disconnected to confirm that it was the problem.

Got one torque convertor bolt out and were turning the flexplate to get to bolt #2 when we noticed that ALL of the transmission to engine bolts were backed out about two threads......

We tightened all those up and reinstalled the convertor bolt that we had just taken out and the vibration was gone. Not sure how all the bolts got that loose, but they did.

We presumed that the previous owner must have had some transmission service or rebuilding done and they left the bolts un-tightened.

Good luck with yours!

[lust4speed]

Who supplied the flexplate? Since you don't know whether the engine was neutral balanced or kept the external balance on the rebuild, it sure sounds like the wrong choice of flexplate was made.

[taalltheway]

We changed the tranny from a TH400 to a TCI 6x....

[lust4speed]

Same holds true for the flywheel -- could be the wrong one for the current balance of the engine. New flywheels are available in original factory external balance or neutral balance, and the one you need depends on how the machine shop balanced out the rotating assembly.

[76TA462]

Not saying your engine needs balancing, but will throw in what I experienced. I had a build on my 455 many years ago and after that I had a vibration that sounds like what you describe. I lived with it for years and it didn't hurt anything. About 6 or 7 years ago I had to rebuild the engine because of more serious problems, and had it balanced at the same time. Vibration gone. That said, as stated above there are other reasons too, and that cost a lot less :>)

[track73]

I have a 56 Buick with a standard trans. The Buick shop manual says to get rid of a vibration due to engine unbalance, is to one at a time put washers on clutch a bolt until the vibration goes away. Then drill the opposite side.

[taalltheway]

Thanks guys, so if it is the wrong flywheel I guess I would have to get a neutral one and see if it gets better? What if it is the other way around?

[Kenth]

Originally Posted by taalltheway

Thanks guys, so if it is the wrong flywheel I guess I would have to get a neutral one and see if it gets better? What if it is the other way around?

Take a good look at the present flywheel and use the other style for replacement.

[taalltheway]

How do i see wich is wich?

[David Jones]

https://www.amazon.com/PRW-1645570-1...ntiac+flywheel

This is what I use. It comes with a removeable weight.

[HWYSTR455]

You should first look at the balancer. If it's an OE replacement type balancer, it's externally balanced. If that's the case, then the flexplate should be externally balanced as well.

Since it's an automatic, it's a flexplate. If you purchased, check the part number, it should tell you if it's internal or external balanced. If you don't know, you should see a weight on the engine side somewhere around the perimeter where the ring gear is welded on. (if it's externally balanced)

If it's a 4L80e, make sure you are using the correct bolt holes in the plate as well as the converter. Most 'e' lockup converters have 2 or 3 holes in each converter pad, and they should all be in the same hole on all pads. Some converters have 6 pads, and only 3 line up to the holes in the flexplate. Make sure no one doctored the plate to 'make' it fit.

Make sure you use the appropriate hardware, and have it spaced away from the trans properly (pull up). With the converter all the way seated into the trans, you should only pull it forward to the flexplate between 1/16 - 3/16", and use grade 8 washers to take up the remaining slack. The bolts are metric, and you may have to doctor the bolt lengths if your converter has blind holes in the pads.

If it still vibrates, look at your balancer and pulleys, I've seen some pretty horrible bent up pulleys cause vibrations. Fans too.

It's not often a 'e' lockup converter is out of balance, just to say.

.

[ta man]

I'm assuming you have ruled out a misfire at 3000rpms?

[taalltheway]

Originally Posted by ta man

I'm assuming you have ruled out a misfire at 3000rpms?

Checked the plugs - all look good - should I change them to be sure?

Changed the wires - makes no difference.

Any other ideas on the electrical front?