Drive shaft balance

[Paul G]

Vibration issues at highway speeds can be a real problem to find. I have already corrected many issues that were causing the vibration. Still trying to get the last bit of it handled.

Vibration can be felt in the floor along with an oscilating sound. It starts around 65 mph on up in speed. The car will only do 130mph. Vibrates from 65 on up.

Pinion angle issues have been sorted. Pinion angles are about 2° between the drive shaft and diff pinion and also 2° between the drive shaft and trans yoke. Tranny has a downward angle, diff pinion has an upward angle, the drive shaft is running downhill to the diff. Trans is as high up, and centered in the tunnel as it can get. It is an A518 although the 727 had vibration issues as well. I have recently added a 2 1/2° degree shim under the axle adding some downward angle to the diff pinion, that did not make any difference in the vibration.

Tires have been balanced twice. Made no difference. I have inspected wheel run out visually with the axle on jacks and wheels spinning. Visually they are straight. Do I need to be more accurate that that? Any ways I have read that wheel issues will come and go at certain speeds. Not my situation. Vibs come in at 65mph and stay.

For the drive shaft, When I did the A518 swap the shaft had to be shortened. The shop that cut it told me it was bent and out of balance. The straightened it and balanced it. All back together and still had vibration issues. After some time passed I pulled the shaft back out and took it to another shop. They said it was straight but out of balance and needed new U-joints. Got it done, put it back in, vibs seemed to be better at first but not completely gone.

Each time the drive shaft was back in the car after a balance it felt like it was smooth but only for the first few miles. Then again something like that is hard to tell if it is real, or just me not paying attention. It feels like the vibs are getting worse as time goes on. So to my question. Is it possible that a drive shaft for some reason may be prone to going out of balance? I am not easy on this Charger. It was a Grandma's car, aint no more. It likes doing burn outs and spirited driving.   

I don't want to throw any more $$ in to a drive shaft that wont stay balanced, if that is possible.
 

[ws23rt]

The best clues you have are that when the drive shaft comes back from the shop it seem ok at first.

That you test the shaft with your engine torque rather hard from time to time is another clue.

Maybe it is time to get a good one (heavy tube size etc.)  Also some drive shaft shops are better that others.
Since I did not sort through your pinion angle information I won't comment on that.
BTW once a straight and true tube has been bent and straightened again it no longer has an even stress along it's length. It is no longer as good as it was new.

[cudaken]

Vibration can be felt in the floor along with an oscilating sound. It starts around 65 mph on up in speed.

Paul does it still have the oscillating sound and feel?

Do you have air shocks by chances? If you do try changing the air pressure, it will change the rear end angle. If it changes at what speed the oscillating is happen at, then something is still off far as drive-shaft angles goes.

Tranny has a downward angle, diff pinion has an upward angle, the drive shaft is running downhill to the diff.    

To be honest Paul, I have no idea if the tail shaft should be pointing at a up, center or at downward angle? But I have read you had the same problem with the 727, by chances did you use the same transmission mount?

The car will only do 130mph

There the Problem! The Charger Is Scared

True story. I had a little old lady come in when I was working at NTB. She told me her Ford Escort started shaking at 85 MPH? (she was in her mid 60's) She asked me why was it shaking? I told her Because it is Scared! 

Well the last part is not helpful but true. 

Cuda Ken

[Big Sugar]

Im suffering the same issue, used to have a tremendous vibration above 65 that kept me out of the throttle seemed to come in earlier under hard acceleration . Rebalanced the tires and rims all round replaced both U joints installed a new bushing in the 727 tailstock, new trans mount reshimmed the rear end to set the pinion 2* lower and the vibration moved up to 75 mph, its not as dramatic but it still occilates and sometime shows up ea little earlier under hard throttle,
I think im gonna swap out my driveshaft for a new one and get a new tailshaft as i suspect the shaft may be a little too loose in the bushing.

Ron

[Paul G]

Vibration can be felt in the floor along with an oscilating sound. It starts around 65 mph on up in speed.

Paul does it still have the oscillating sound and feel?

Do you have air shocks by chances? If you do try changing the air pressure, it will change the rear end angle. If it changes at what speed the oscillating is happen at, then something is still off far as drive-shaft angles goes.

No air shocks. It has pretty stiff leaf springs that set the rear up a bit from stock.

Tranny has a downward angle, diff pinion has an upward angle, the drive shaft is running downhill to the diff.  

To be honest Paul, I have no idea if the tail shaft should be pointing at a up, center or at downward angle? But I have read you had the same problem with the 727, by chances did you use the same transmission mount?

The A518 requires a totally different mount position on the trans. Stock mount was cut off the cross member, used a flat type mount on a fabricated plate welded to the cross member to get the mount in the new position for the A518.

The car will only do 130mph

There the Problem! The Charger Is Scared

True story. I had a little old lady come in when I was working at NTB. She told me her Ford Escort started shaking at 85 MPH? (she was in her mid 60's) She asked me why was it shaking? I told her Because it is Scared!  

Well the last part is not helpful but true.  

Cuda Ken

Just wondering if any one else has had a DS that would not stay in balance. It just may be time to call Denny's.

[fy469rtse]

Bet the rear bush is now needing to be changed out when you put that new drive shaft in, try dts as well , go thick wall ? Are you using the large universals 7290 big block , pay attention to the universals you use , get the best , no point skimping on this area

[ottawamerc]

Ok if someone finds the solution to this it HAS to become a sticky On my drive home last nite from Moparfest getting the soothing vibration from my car I got to thinking, is it possible that we are just used to our new rides being smoother and 40+ yrs ago this type of vibration was the norm?

Scott

[Big Sugar]

No im pretty sure we're missing somthing, it is definatly a driveline related issue i just wonder if its a flex plate or convertor issue. Trouble i it definatly sounds like its right between the seats, seems like its a harmonic issue in the driveshaft. May have to replace the driveshaft.


Ron

[ws23rt]

No im pretty sure we're missing somthing, it is definatly a driveline related issue i just wonder if its a flex plate or convertor issue. Trouble i it definatly sounds like its right between the seats, seems like its a harmonic issue in the driveshaft. May have to replace the driveshaft.


Ron

The clues you have do point to the driveshaft. Especially that it is aggravated by adding throttle. It would change the pinion angle some under load.

It seems less likely to be flex plate or convertor because one would expect it to show up in a lower gear/lower speed. (rpm related).

[ottawamerc]

Hey Ron don't bother with the converter flexplate or drive shaft I already tried that in desperation and it didn't fix it! As for my earlier comment on the good vibrations being the norm I was definay wrong cause the tail shaft leaked a lot of oil out ! It's gotta be the pinion angle

Scott

[flyinlow]

Does it vibrate the same above 65mph in third as it does in OD?  Does being in lock up mater to the vibration?

[Dodge Don]

Hard to tell what is "normal". Typically I avoid the highways like the plague because of my 3.91 gears but the drive home from Moparfest required a run on the 401. When I'm on the highway I usually try to keep it around 3500 RPM which is around 55 MPH for me (everyone passes me like I'm standing still  )....I get a rythmic ocilation...more of a drone.....hard to explain.....car feels fine, runs great but you get the mmmmMMMMMmmmmmmMMMMMMmmmmm sound. I was thinking of swapping in an aluminum driveshaft to shed a few pounds, reduce the rotating mass and get a more balanced shaft? 

[MSRacing89]

Don't want throw a wrench into the mix here but a rhythmic vibration especially at a certain RPM is a lot of times related to the Harmonic Balancer. 

Does it oscilate if you are sitting in the driveway with no load at a that RPM?

[Dodge Don]

Don't want throw a wrench into the mix here but a rhythmic vibration especially at a certain RPM is a lot of times related to the Harmonic Balancer. 

Does it oscilate if you are sitting in the driveway with no load at a that RPM?

Not for me.

[1BAD68]

I get the same oscillating vibration. Starts around 60-65 thru about 85mph where it just sort of goes away.
Sounds like going over a series of rumble strips but not as loud.
Definitely not tires or transmission as I changed both with no changes.

[Dodge Don]

Kind of like the drone sound you hear on old WW2 movies from inside a bomber on it's way to drop its load

[john108]

This may not be applicable but: I had a problem once where I had a lot of vibration at lower to medium speeds but when at highway speeds, it smoothed out.  The problem turned out to be the U-Joints.  Some Rollers had fallen out of the bearings.

[Paul G]

I get a rythmic ocilation...more of a drone.....hard to explain.....car feels fine, runs great but you get the mmmmMMMMMmmmmmmMMMMMMmmmmm sound.   

That is the sound. It was much more noticeable and came in at a slower speed until I got the pinion angles aligned better. Make sure your tranny is centered in the tunnel. Pinion alignment is not just verticle or "up/down" like we see things, it also has a "left/right" element. My tranny was sitting way off center. Getting the tranny centered in the tunnel made a big difference in reducing the vibration.

[1970Moparmann]

This may not be applicable but: I had a problem once where I had a lot of vibration at lower to medium speeds but when at highway speeds, it smoothed out.  The problem turned out to be the U-Joints.  Some Rollers had fallen out of the bearings.

Funny how I was just talking to a friend when I saw this thread.  My Coronet is doing the same thing.  A buddy said that it is probably an improper seated U Joint.  Anyways, I'm taking the drive shaft out tonight, getting a new U joint and having the shaft balanced to be safe.

I'll report back........

[Big Sugar]

Well mike check that the tranny is centred while your under there .....Paul G may have something there.    I guess you would need to back to the engine mounts and loosen them off to get the tranny sitting centre in the tunnel.


Ron

[ottawamerc]

How can you tell if it is centered properly ? Just a visual thing?
Scott

[MaximRecoil]

Ok if someone finds the solution to this it HAS to become a sticky On my drive home last nite from Moparfest getting the soothing vibration from my car I got to thinking, is it possible that we are just used to our new rides being smoother and 40+ yrs ago this type of vibration was the norm?

Scott

I don't think so. My '69 is a former "General Lee":



And it has been jumped through the air, suffering a pretty hard nose-forward landing at some point in the distant past. Some previous owner more or less straightened it out, but the crumples and waves in the steel (e.g., inner fenders, subframe rails) where the nose had bent upward can still be seen, the underside of the K-frame is still dented in, the front valance is still mangled on one side, the radiator chair is bowed, the driver's side fender was mangled and then straightened/Bondo'd, the frontend bushings and front shocks were utterly trashed (I replaced all the bushings, sway bar links, etc. in the frontend, along with the shocks, then got a frontend alignment at my local Chrysler dealership), and so on.

This is what it looked like just before I hauled it out of the Maine woods in 2011, where it had rested since 1994:



In any event, that car (318 automatic, 2.71:1 gear ratio in the rearend) goes down the highway at e.g. 75 slick as hell; not a hint of vibration, and it tracks straight too. I don't think the transmission, driveshaft, or rearend has ever been messed with by any of the previous owners. The only thing I've done in those areas is replace a missing rearmost U-joint (the driveshaft had been disconnected for towing at some point, and the U-joint was long gone), and replace the axle grease seals in the rearend, because one of them was leaking grease onto my brakes.

So if my car, which has had a very rough life to say the least, can go down the highway without vibrations, they could no doubt do it when new, and yours can no doubt do it too, if the problem can be pinpointed.

[Cooter]

Ok if someone finds the solution to this it HAS to become a sticky On my drive home last nite from Moparfest getting the soothing vibration from my car I got to thinking, is it possible that we are just used to our new rides being smoother and 40+ yrs ago this type of vibration was the norm?

Scott

Winner, Winner, Chicken dinner. Interstate speeds were ALOT slower, and back then I can't remember anybody ever telling me that they "Didn't realize they were going 80 MPH it was so smooth" as they tend to do today. You KNEW when you were going that fast back then because you were wrestling an alligator at those speeds to keep it straight. Once you begin to swap around all these OD trannies, everything must be re-engineered in order to be back where the driveshaft speeds can handle being in OD with like 3.55-4.10 gears.

[1970Moparmann]

Well mike check that the tranny is centred while your under there .....Paul G may have something there.    I guess you would need to back to the engine mounts and loosen them off to get the tranny sitting centre in the tunnel.


Ron

Ron, I did a few years ago and all looked good.   

[MaximRecoil]

Winner, Winner, Chicken dinner. Interstate speeds were ALOT slower, and back then I can't remember anybody ever telling me that they "Didn't realize they were going 80 MPH it was so smooth" as they tend to do today. You KNEW when you were going that fast back then because you were wrestling an alligator at those speeds to keep it straight. Once you begin to swap around all these OD trannies, everything must be re-engineered in order to be back where the driveshaft speeds can handle being in OD with like 3.55-4.10 gears.

Except, my car is smooth, not a hint of vibration, and tracks straight at 75 or 80 MPH, and it has been through hell. See above. The indicators of high speed in my car comes from wind noise and a somewhat loud exhaust. New cars are simply a lot quieter at those speeds; better aerodynamics, better sealing, more sound-deadening insulation, and quieter exhaust compared to my car. However, if you took a 1969 Cadillac, Lincoln, or Imperial down the highway, I'll bet it would be just as quiet as most new cars, and you could easily not realize you were doing 80.

As for interstate speeds being a lot slower back then: not necessarily true. For example, in my state:

The Maine Turnpike had a posted speed limit of 70 mph in the early 1970s, but as Maine then had no law against traveling less than 10 mph over the posted speed, the de facto speed limit was 79 mph.

The speed limit in Maine on I-95 and the Maine Turnpike is now 65 MPH, and you can get a ticket for exceeding it by any amount. As of 2 years ago, there is one section of I-95 in Maine (from Old Town to Houlton, about 100 miles) that has a 75 MPH speed limit, but that is still not as high as the de facto speed limit of the early '70s here.