1970 440 Challenger Vibration @ 2700-3000 RPM ONLY

[440SMOKE]

303 mopar - I tried the drive to neutral trick. Once the mph dropped a bit the vibration went away but my rpms did go up a bit too so was hard to keep exact rpms. The pulsing did go away.

Shane Kelley - isn't the diff supposed to point to the frame of car and transmission point to ground? So if diff points 2 degrees up and transmission 2 degrees down they are parallel?

[dodj]

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

Flex plate is the same on internal or external balanced motors. The weights are on the converter.

[mopar jack]

The back of your converter looks to have an extra hole in the mounting pad. I would pull the 4 bolts from the flex to  converter and make sure that the flex plate doesn't have any out of round or enlarged holes. The flex plate and converter are indexed and proper alignment is critical. The flex plate should not need any balance so that weight is wrong.

[750-h2]

303 mopar - I tried the drive to neutral trick. Once the mph dropped a bit the vibration went away but my rpms did go up a bit too so was hard to keep exact rpms. The pulsing did go away.

Shane Kelley - isn't the diff supposed to point to the frame of car and transmission point to ground? So if diff points 2 degrees up and transmission 2 degrees down they are parallel?

No, pinion also points to the ground . Here is a pic of -7 degree pinion angle. You want -4 degrees same principal applies.

[440SMOKE]

Thanks 750-h2 - wow I have done it all wrong and I thought it was perfect? I researched and researched.

Question - so how do I get the transmission shaft to parallel the pinion yoke shaft if pinion yoke is pointed down to ground? I doubt I can get transmission to point up especially with gear vendor installed without hitting frame or tunnel.  I would have to drop engine mounts to get transmission to point up but that makes oil pan clearance and issue?

[Chryco Psycho]

The balancer is for a steel crank , no way to tell what the crank is though

[dodj]

The balancer is for a steel crank , no way to tell what the crank is though

I think if it was a forged crank, it would not vibrate when he took the homemade converter weight off. I think he has an internal balance damper, a cast crank and a Magyver'd torque converter.
IMO, buy an external balance damper, external balance weight kit for the converter. Install and you will likely be good.

[Chryco Psycho]

It seems if the rpm stayed the same but the driveline slowed in neutral & the vibe went away that the vibration is Not in the engine but behind it instead

[fantum]

Years ago, I had this exact problem with my old 340 'Cuda.  Turned out the driveshaft needed to be balanced.  Once I had that done, all of the vibrations went away.  At this point, a relatively easy and not-too-expensive way to check an item off of your list of possible causes.

I hope you find the fix soon, as I know this problem is very frustrating.



MIKE/fantum

[440SMOKE]

Thanks Fantum - it is very frustrating and would like to get this resolved!!   

This is my second drive shaft and the one in my car now is built from Bears Performance so im guessing it should be good?

Chryco Psycho - I am finally putting this cars history together and talked to the engine builder that did engine for the guy that owned the car before me and he says it is externally balanced so we do know that fursure now.  He did say that on some engines that they left the internally balanced harmonic balancer as it wasn't a big difference so they left it.  Also he said that if it was a harmonic balancer issue it would vibrate all the time?  I do have the balance card now for future reference and can get things weighed up properly now without a full teardown of the engine. The Engine shop was the ones that welded that chunk of steel on the flexplate to balance engine. What im guessing is when the restore shop installed a new higher stall converter the flexplate needed to be replaced too and they took the steel off of the old flexplate and welded onto the new flexplate by just eye balling it?  That's what it sounds like anyway. But if it is a engine vibration issue like it sure seems with an incorrectly balanced flex plate why doesn't it vibrate all the time?     

Question - So when I drop car into neutral and vibration goes away, what does it mean its now behind engine?  Where could it be, where should I start looking?  Could it be a balance issue in torque converter?

Thanks
440SMOKE

[440SMOKE]

The balancer is for a steel crank , no way to tell what the crank is though

I think if it was a forged crank, it would not vibrate when he took the homemade converter weight off. I think he has an internal balance damper, a cast crank and a Magyver'd torque converter.
IMO, buy an external balance damper, external balance weight kit for the converter. Install and you will likely be good.

Dodj - I totally feel the same as you and I feel that will fix us up too but just one item still concerns me still.  Its a harmonic pulse rather than a continuous vibration so would fixing those components remove the pulsing feel that I feel in the seat of my pants at a certain RPM/MPH in Drive only?  Or am I not diagnosing the felt vibration properly in neutral and a harmonic pulse is a part of a continuous vibration?  Its a brain stumper fursure.  Thanks 

[Chryco Psycho]

if the engine rpm is maintained but the driveline rpm drops down & the vibration stops , it should not be the engine ,
There is a drive line video on this site somewhere that I posted
Here it si https://www.youtube.com/watch?v=gmV4qwLfOMY

[dodj]

It's the engine.  Get the proper weights on it for an externally balanced motor. I mean it only makes sense to get the proper parts on it. You have found out it is an externally balanced motor, so leaving an harmonic balancer meant for an internally balanced motor makes no sense at all. If they could effectively balance a motor with weights just on the torque converter, Mopar would have only made one style of harmonic balancer.