Strange Vibration over 3000 RPM

[Paul G]

I dont drive over 3000 RPM very much, but the other night I had the Charger on the highway at 65 MPH and it had a very disturbing vibration, kind of loud groan almost like driving over those cuts in the shoulder of the road to wake you up. I have narrowed it to engine RPM more than vehicle speed because I can hold it in 1st or 2nd and run the RPM's over 3000 and there is the vibration. On the highway at 65 MPH it kind of comes and go's in an oscilating fashion. When held in a lower gear and run over 3000 RPM it is a constant vibration. Runs sweet and smooth when driving down the road normally. 

The drive train is:
360
727
8 3/4, 3:90 gears
March pulley set with A/C
Schumacher Torque Strap
Hooker competition long tube headers
New exhaust installed last week, 2 1/2" with Pypes x-pipe through turbo mufflers

[jeryst]

Wrong torque converter? I found out that a 360 requires an externally balanced torque converter.

Maybe the drive shaft or a universal joint.

[elacruze]

When did it start?

I was stumped once by a similar event, turned out to be the serpentine belt. Check the tension, and rev it up with the hood open-be certain the A/C is on. A/C compressors have a resonant frequency which translates into the serp belt.

[Paul G]

Both serp belts are new and tight. I am not too pleased with the fit of the March pulley set. I'll take another look at it.

I question the torque converter since it is RPM related. How can I tell if I have the right one? Externally balanced?

[bobs66440]

Did it just suddenly start?

What type of harmonic balancer do you have? I've seen them come apart. The outer ring may be loose from the hub.

Also, the flexplate bolts may be loose. That has happened to me.

Also, will it do it sitting still in the driveway?

[Highbanked Hauler]

Both serp belts are new and tight. I am not too pleased with the fit of the March pulley set. I'll take another look at it.

I question the torque converter since it is RPM related. How can I tell if I have the right one? Externally balanced?

The converter that came off my 360 has a  metal block welded to it. I don't know if they all do.

[Brass]

I second the driveline or u-joint suggestion.  I would get those checked.

[NMike]

if it is RPM related, it can't be transmission or driveline. can only be engine or torque converter.

if it is SPEED related, won't be engine related, will be transmission or driveline.

[Paul G]

if it is RPM related, it can't be transmission or driveline. can only be engine or torque converter.

if it is SPEED related, won't be engine related, will be transmission or driveline.

I am following the engine and torque converter path first. I put my hands on the driveshaft and exhaust. very tight, no looseness or slop.

Did it just suddenly start?

What type of harmonic balancer do you have? I've seen them come apart. The outer ring may be loose from the hub.

Also, the flexplate bolts may be loose. That has happened to me.

Also, will it do it sitting still in the driveway?

I really cant say how long it has been doing it. I have been correcting problems as I go. I only bought the car 6 months ago. So far I have had the exhaust replaced due to rattling Flowmaster cans and tail pipes that were touching the under body. That made for a very rough and noisy ride. It's fixed now. The engine was running poorly, bad wires and carb way out of tune. Those problems are fixed. Now I get this vibration over 3000 RPM. I would assume it has been there all along.

Checked the flexplate bolts, all are tight. The torque converter has a weight welded on it right next to a tab for a flex plate bolt. Is that the balance weight?

Looked at the harmonic balancer. Stock type. It looks newer, has nice blue paint, I can see a layer of rubber on the back side, between the two halves. It does not looked like it is coming apart at all.

Yes it does vibrate in the driveway surprisingly. Anything over 3000 and you can feel the engine vibrating. ??

[jeryst]

Well, if it vibrates when you are just sitting in the driveway revving it, then it has to be some type of rotating mass problem in the engine or tranny.

Is it possible you do not have the proper harmonic balancer?

Have you checked your fan? Maybe one of the blades is missing, bent, etc. Course that's easy to check by just removing the fan.
If you had to, you could remove the belts and pulleys one by one and try it. If its still there, then it has to be the balancer,
torque converter, or something internal to the engine.

Did you build the engine? Hopefully, its not something like an improperly balanced crankshaft or bent distributor shaft.

[bobs66440]

Is it possible you do not have the proper harmonic balancer?

Now that you mention it, I do recall a thread on the 66-67 Charger site about this (site is down now temporarily). There are two different ones: internally balanced and externally balanced. If you have the wrong one for the crank (cast or forged I think, can't remember which is for which) that will definitely cause a vibration.

[Paul G]

Did you build the engine? Hopefully, its not something like an improperly balanced crankshaft or bent distributor shaft.

The 360 was built by Phoenix Engine Builders 10 years ago. I have some documentation that is very hard to read. Cant read the specs on what they put together.

Is it possible you do not have the proper harmonic balancer?

Now that you mention it, I do recall a thread on the 66-67 Charger site about this (site is down now temporarily). There are two different ones: internally balanced and externally balanced. If you have the wrong one for the crank (cast or forged I think, can't remember which is for which) that will definitely cause a vibration.

Is a 318 balanced differently than a 360? It was originally a 318 car. They may have used the accessories and the balancer from the old 318? Is there a way to tell if the harmonic balancer I have is correct for a 360?

[Paul G]

Have you checked your fan? Maybe one of the blades is missing, bent, etc. Course that's easy to check by just removing the fan.
If you had to, you could remove the belts and pulleys one by one and try it.

The fan is a stock 5 blade with a clutch, and stock shroud. The blades are all there. With the engine off, should I be able to rotate the fan easily? 

[bobs66440]

Did you build the engine? Hopefully, its not something like an improperly balanced crankshaft or bent distributor shaft.

The 360 was built by Phoenix Engine Builders 10 years ago. I have some documentation that is very hard to read. Cant read the specs on what they put together.

Is it possible you do not have the proper harmonic balancer?

Now that you mention it, I do recall a thread on the 66-67 Charger site about this (site is down now temporarily). There are two different ones: internally balanced and externally balanced. If you have the wrong one for the crank (cast or forged I think, can't remember which is for which) that will definitely cause a vibration.

Is a 318 balanced differently than a 360? It was originally a 318 car. They may have used the accessories and the balancer from the old 318? Is there a way to tell if the harmonic balancer I have is correct for a 360?

Oh, it's a 360, sorry, I was thinking 383/440 for some reason.
It still may be an issue. I don't know much about the 318/360's sorry.

[bobs66440]

Did you build the engine? Hopefully, its not something like an improperly balanced crankshaft or bent distributor shaft.

The 360 was built by Phoenix Engine Builders 10 years ago. I have some documentation that is very hard to read. Cant read the specs on what they put together.

Is it possible you do not have the proper harmonic balancer?

Now that you mention it, I do recall a thread on the 66-67 Charger site about this (site is down now temporarily). There are two different ones: internally balanced and externally balanced. If you have the wrong one for the crank (cast or forged I think, can't remember which is for which) that will definitely cause a vibration.

Is a 318 balanced differently than a 360? It was originally a 318 car. They may have used the accessories and the balancer from the old 318? Is there a way to tell if the harmonic balancer I have is correct for a 360?

Oh, it's a 360, sorry, I was thinking 383/440 for some reason.
It still may be an issue. I don't know much about the 318/360's sorry.

[bull]

Make sure your bellhousing bolts are tight. I had the same issue when I first got my Charger except it was vibrating at about 2000 rpm moving or not.

[skip68]

Check for broken motor or tranny mounts. 

[Just 6T9 CHGR]

I have pretty much the same vibration at between 60-68 mph.....lower it doesnt do it...higher it doesnt do it (as bad)
Sounds like this.....mmmmm....mmmmm.....mmmmm.....mmmmm

Recently I had to swap back in a friends spare stock SG 3:23 rear because the new Sure-Grip I installed in my 3:55 housing last season blew up.   Took the 3:23 rear on the highway & guess what.....vib 97% GONE!!

Im tending to think the aftermarket US Gear 3:55's have something to do with it.....  

[Paul G]

Check for broken motor or tranny mounts. 

Checked em today. Motor and tranny mounts are tight. Put a floor jack under motor and raised the whole front end, same for tranny.

Make sure your bellhousing bolts are tight. I had the same issue when I first got my Charger except it was vibrating at about 2000 rpm moving or not.

They were not super tight. I put another 1/2 turn on them with a standard box wrench. We'll see if that makes any difference.

[Paul G]

This is a pic of my damper. It looks to have a weight on it. Is this an externally balanced damper?

[71383bee]

that is an externally balanced damper.