1970 440 Challenger Vibration @ 2700-3000 RPM ONLY

[440SMOKE]

Hello Mopar experts!!  I need help please. 

I have a new to me 1970 Dodge Challenger with a 440 and a 727 automatic transmission.  I bought this car and the engine was all done by the guy that owned it before.  This car did not leave the garage very much is what I am guessing as there were belt issues that I had to fix so no way he could have ran it that way without a tow truck following him.

I have a harmonic pulsing vibration in the seat of my pants at 2700-3000 rpm.  It does not vibrate or pulse at any other RPM.  Its not a violent pulse but it is there and I want to fix it. I have done all the basics like driveline angle (now perfect), new driveline, new transmission mount and also rebuilt the rear end.  Engine mounts are brand new and nothing touching anywhere to cause vibration.  I also ensured there were proper shims in the gear vendor which now its perfect.  The transmission was also supposedly rebuilt by the restore place and the engine was not touched besides new Performer RPM intake for the FAST fuel injection I wanted on the car.  Nothing to date has fixed my issue yet and i'm still in the hunt for this vibration.  I was under the car the other day looking around even in more detail and I pulled the transmission inspection plate and found a chunk of steel welded to the flex plate?  I was kinda in shock to see this.   

The weight weights 3.7 ozs.  There was 2 out of 3 welds that were cracked so I tacked them back up hoping this was possibly the vibration I was feeling.  No luck and still vibrated after I ran the car again at that RPM.  So I pulled this steel weight hoping that it wasn't supposed to be there and then car really vibrated bad so I stopped immediately. 

My question is - How do I fix this properly and the right way?  What do I need to do?  To me, welding a chunk of steel seems like not the right way to me as obviously it isn't the right weight or in the wrong spot as my car still vibrates with it on.  My data sheet for the engine says that it was balanced but it does not say anything about being internally balanced or externally balanced.  I do not see anymore weights on my torque converted welded on either.  This motor looks like its a 74 year vintage from the block stamp so it should be a cast crank which would mean externally balanced unless the engine rebuilder balanced internally which I do not know? The harmonic balancer mounted on my engine looks like an internal balancer as it is fully round and no cups or grooves or divits on the back side towards engine for mounting external weights?   I believe my torque converter is a 3000 stall. 

What do you guys think is my issue for this vibration felt? 

Thanks for your help. 

[Cuda Cody]

It sounds like an internally balanced or externally balanced issue to me.  If your engine is internally balanced and your torque converter is not correct you might feel something like this.   

[dodj]

Being a '74, my guess is you need an harmonic balancer for an externally balanced engine AND the weight kit for your torque converter. The weight kit comes with a template for where to position the weights and you weld them on.
This guess is based on when you removed the homemade weight from the torque converter, the vibes got worse. So I think you have an externally balanced motor.

[303 Mopar]

Have you tried running it up the the RPM and then put it in neutral? This will tell you if it's the engine or trans back.

[440SMOKE]

Thanks everyone for your replies! Really appreciate it!

I haven't tried shifting it from drive to neutral which is a good test but have ran in up to rpm in neutral and car doesn't vibrate like a pulsing like it does when it's in drive. It's different or not existent in neutral -  maybe just a hint of vibration but minimal if any.  Definitely way different than when its in drive. Also if I pull driveshaft and run it up to rpm in drive it doesn't pulse either which lead me to all the driveshaft and rear troubleshooting I done previous.

With the steel piece removed if I run motor up in neutral it vibrates bad. It almost seems to me that the steel piece was close to proper weight but just out a bit and that bit shows itself at 2700-3000 rpm. I'm not sure.

[Chryco Psycho]

 
Welcome to the site , as well
Try shifting into neutral & coasting when it is vibrating if it continues it is in the driveline , if it stops it has to be the engine & converter .
If it is the engine it should also vibrate  the given rpm while sitting still .
Once you determine where the vibration is we can narrow it down , you need to know if you have a steel crank or cast & what damper you have , steel crank is approx 1" thick cast is thicker with an offset plate on the front of the damper . Even if the damper is correct if the engine has been rebuilt with lighter pistons using the correct parts will not fix the vibration .
My guess is the engine is out of balance if removing the converter weight changed it that much
worst case you may have to pull the engine , disassemble it & have the rotating assy properly balanced , anything else is a guessing game at this point .

[IRON MAN]

I have learned if you feel vibration in the seat of your pants it is not an engine or transmission issue. The vibration is caused by the driveshaft back. Believe in trying process of deduction. Rotate wheels and tires and take up to fwy speeds. If that doesn't help tow car up to 70 mph without drive shaft. If that doesn't eliminate vibration check for bent axle flange. Inspect pinion yoke for distortion. Check transmission output shaft angle...should face up 2*, check pinion angle.....should be 2* downward. These angles are a general rule of thumb.  Has the car been lowered? Also, the driveshaft should be precision balanced at 3000 rpm or higher when there is a vibration issue. Good luck!

[Jim AAR]

I would also have your Tires checked for Balance, especially the Rear tires, out of balance or separated (if they're radials) tires can cause vibrations and shimmies.... 

[Chryco Psycho]

If you have BFGoodrich tires that is very likely your problem but generally they will not be vibrating in such a limited rpm range

[Shane Kelley]

Bad pinion angle will cause a vibration at certain speeds.    Does the vibration happen at a certain speed?

[mopar jack]

Had a vibration like that in my 73 challenger and never resolved it. It had an Art Carr torque converter. Pulled the converter and sold the car. A few years later I built my current Barracuda to drag race in the street brackets and installed the Art Carr converter. Yep the vibration was back in a different car. Sent the converter to a shop where they cut it open and found some broken parts inside.

[440SMOKE]

Thanks Everyone!!

When I am running my car I am doing it on jack stands in my shop as it is still winter where I live.  I always run the car without tires to ensure its not a tire issue and have ran the car without axles in either and did not help.  The only time it goes away is with driveline out?

Im guessing and will try this tonight by running it in my shop is that the vibration will go away when I shift it from Drive at 2700-3000 RPM to Neutral as this should be the same as just reving the motor in neutral to 2700-3000 RPM?  I will try it and post back here tonight. 

Please see attached pictures for Harmonic balancer.  I think it is an internally balanced harmonic balancer but hoping you guys can tell me fursure please.  Also can anyone tell me from picture possibly if this is a cast or forged crank?  It would be awesome if they just had the wrong balancer on the motor but like Chryco Psycho said - it still may not fix issue as may have lighter internal components in engine.  Isn't there a way to balance with a B&E flex plate that allows external weights to fine tune if I did have lighter engine parts or bad balanced torque converter?   

Iron Man/Shane Kelley - I have my pinion perfect now.  I adjusted transmission and Rear-end.  Transmission is 2.5 degrees down and Rear-end pointed 2.4 degrees up.  Both Diff and Transmission have a running operating angle of 1.1 degrees.  Brand new drive shaft from Bears performance that came with new greaseless U joints.  Vibration only happens at 2700-3000 RPM which is 60 MPH with Gear vendor Overdrive off or 70 MPH with gear vendor overdrive on.  Both these speeds are at same RPM.     

Chryco Psycho/Jim AAR - only run car with tires off to reduce rotating mass and also remove as many variables as possible.  Have even ran car without axles to ensure they are ok too with no help.  I have pulled Diff apart and put a new master kit in and clutch packs for my positraction. 

[Shane Kelley]

 "I have my pinion perfect now.  I adjusted transmission and Rear-end.  Transmission is 2.5 degrees down and Rear-end pointed 2.4 degrees up.  Both Diff and Transmission have a running operating angle of 1.1 degrees."

Pinion angle needs to be down not up. So you have your pinion already up 2.4 degrees and when you accelerate that pushes it even higher. Could be as much as 4-6 degrees and that can play havoc with the u joints. I'm not saying this is your vibration problem but it is definitely a problem.

Below is from Dr. Diff.

[303 Mopar]

Well your flexplate is for an internal balanced engine, so lets hope the crank and balancer is too!

[Katfish]

Please post what you find.  I have almost the same exact problem.
Car only vibrates between 75-85 mph or about 2800 rpm.
Little different combo, 340 with 518 OD transmission.
I suspect a TC or driveshaft problem