VIBRATION!!! I FOUND IT!!!!!!

[RECHRGD]

Some of you may remember the vibration that I've been chasing for two years now.  I've blamed it on the Gear Vendors unit creating pinion angle problems, but now I'm not so sure.  The vibration comes on between 65 and 75 mph and goes away after that.  I've gone to different shops and all of their "experts" have tried different pinion angles with no improvement.  The vibration is more pronounced under power than not.  It is not severe, but you can feel it on your butt and the rear view mirror starts to get fuzzy.  Here's a list of what I've tried to date:
1- Pinion up 2 degrees, left tranny angle alone.
2- Pinion down 2 degrees, left tranny angle alone.
3- Pinion down 4 degrees, left tranny angle alone.
4- Pinion down 4 degrees, raised tranny mount 1/4".
5- Pinion down 8 degrees, raise tranny mount 3/8" (cannot raise tranny any more).
6- Pinion up 2 degrees, tranny down 2 degrees.
7- Had driveshaft rebalanced.
8- Had new driveshaft built and balanced.
9- Ran it up to speed on jack stands without the rear wheels on.  No change.
10- Had all tires balanced.  No change.
11- Ran it up to speed without driveshaft.  No vibration!
12- Tried all the little tricks recommended by G/V. (straps on driveshaft, etc.).  No change.
13- Replaced Schumaker polylock engine and tranny mounts with stock units.  Softened the vibration and made it more comfortable to drive, but definitely did not fix the problem.
14- Put new tighter yoke on tranny (G/V unit).  No change.

I'm at my wits end with this thing!  The yoke on the pig is tight with no slop at all that I can feel.  With all the different pinion angles that have been tried, wouldn't that have changed the speed at which this happens?  It just seems odd that the vibration comes in at exactly the same speed, no matter what the angle is.  I've got the car home for the winter now and have the luxury of being able to work on it while on a 4 post lift.  Any ideas???  This really has taken the fun out of cruising at highway speeds for two years now.  Thanks,  Bob

[RECHRGD]

OOOOPs!!!  I forgot.  Also put new u-joints on with the same result.  No change.  Bob

[Back N Black]

Torque Converter? I had a Roadrunner that did the same, but eventually got worse. Replaced the converter and problem solved. Something to think about. 

[ChargerST]

The problem is somewhere after the transmission (as there is no vibration without the driveshaft). My Charger is doing the same ( didn't get around fixing it yet) - I've been told to balance the driveshaft but that doesn't seem to be the problem with your car as you already replaced the driveshaft and the U-joints.

something to do with the rear axle?  if you have one lying around maybe swap it out for a test run.

When did the vibration start?

[RECHRGD]

The problem is somewhere after the transmission (as there is no vibration without the driveshaft). My Charger is doing the same ( didn't get around fixing it yet) - I've been told to balance the driveshaft but that doesn't seem to be the problem with your car as you already replaced the driveshaft and the U-joints.

something to do with the rear axle?  if you have one lying around maybe swap it out for a test run.

When did the vibration start?

The vibration started after the gear vendors unit was installed.  But, I'm not 100% positive that it started right after that.  It could have shown up a month or two later.  Bob

[charger Downunder]

Bent rear axle my bet ?

[tan top]

yeah was just thinking axle or drive shaft ...........

[RECHRGD]

Bent rear axle my bet ?

Wouldn't a bent axle just get worse the faster you went?  This thing starts at 65 and is over at 75.  I can cruise all day at 90 and be smooth as glass.  Bob

[lisiecki1]

something out of balance inside the g/v unit?  harmonic resonance due to the change in surface area of rotational mass under the car?(did the 2nd gens have the harmonic block off of the back of the crossmember like the 3rd gens?)

[RECHRGD]

something out of balance inside the g/v unit?  harmonic resonance due to the change in surface area of rotational mass under the car?(did the 2nd gens have the harmonic block off of the back of the crossmember like the 3rd gens?)

G/V said that there is really nothing in there that could be causing the problem.  I tend to believe them as it's a pretty simple deal.  No, there is no harmonic block at the crossmember on 2nd gens.   Thanks, Bob

[lisiecki1]

well....it would be a pain, but you can change the tailshaft back to the original and see if it goes away.........

[RECHRGD]

well....it would be a pain, but you can change the tailshaft back to the original and see if it goes away.........

Yea, I know.  I still have the old stuff.  I was hoping not to have to go through that exercise, but it may come to that.  Bob

[lisiecki1]

if you do please post your results, I was thinking about getting a GV unit when I get the car done.....

[RECHRGD]

Oh, don't worry.  If I find that it's the G/V unit causing all this grief, I'll be making plenty of noise.  I haven't really been leaning that way because the vibration is at the same speed whether the overdrive is on or off.  But, of course, the driveshaft is connected to that thing.   Bob

[elacruze]

I don't know all the history of your problem, so I apologize if I review previous ideas. We had a similar vibration in a race car we chased for a long time.
The short story is that the high-dollar transmission yoke turned out to be out of balance by enough to create an out-of-plane imbalance which didn't show up on the balancer, but showed in the car because of the clearance in the tailshaft bushing. The front of the assembly wobbled because the balance weight on the shaft was ~6" behind the heavy spot in the yoke. I also had a pickup truck that had a bad shake which turned out to be slightly loose pinion bearings, which allowed the same problem as the out of balance yoke.

After such a thorough investigation, I'd balance all of the driveshaft components separately, then assemble and rebalance dynamically. Remember too that the shaft is spinning at least as fast as engine RPMs, so balancing the shaft to only 3000 rpms isn't adequate.
Double check the pinion preload if you haven't already.

If you haven't already, have them double check the clocking on the shaft yokes.

[RECHRGD]

I don't know all the history of your problem, so I apologize if I review previous ideas. We had a similar vibration in a race car we chased for a long time.
The short story is that the high-dollar transmission yoke turned out to be out of balance by enough to create an out-of-plane imbalance which didn't show up on the balancer, but showed in the car because of the clearance in the tailshaft bushing. The front of the assembly wobbled because the balance weight on the shaft was ~6" behind the heavy spot in the yoke. I also had a pickup truck that had a bad shake which turned out to be slightly loose pinion bearings, which allowed the same problem as the out of balance yoke.

After such a thorough investigation, I'd balance all of the driveshaft components separately, then assemble and rebalance dynamically. Remember too that the shaft is spinning at least as fast as engine RPMs, so balancing the shaft to only 3000 rpms isn't adequate.
Double check the pinion preload if you haven't already.

If you haven't already, have them double check the clocking on the shaft yokes.

Thanks for the ideas.  All the yokes are tight.  I'm going back to the driveline guy today and have him cut a 1/4" off of the trans yoke.  With the pinion angle at almost zero it was too tight.  But the problem was still there even with a shorter driveshaft.  I'll have him spin it again, but, as I recall, he took it over 6000rpm with no problems.  I've taken all shims and washers out of the equation and the driveline is now sitting right where it was before the G/V installation.  With the shorter D/S the angles will be a little greater.  I'll try to get the angles to replicate what they would have been with the original longer D/S and see what happens.  If that doesn't change anything, then I think I'll just have to pull the G/V out of there and return everything back to stock.   Bob

[pettybird]

Bent rear axle my bet ?

Wouldn't a bent axle just get worse the faster you went?  This thing starts at 65 and is over at 75.  I can cruise all day at 90 and be smooth as glass.  Bob

Problem solved!


pull a brake drum and look for odd wear patterns indicating a wobble in the axles, if you have one.  how about swapping tires front to rear, or trying another pair altogether?  it would be silly if you're chasing a radial pull with drivetrain parts. 

good luck!

[bull]

You probably already know this but if your wheels are the two-piece reproductions, like most repro Magnums, they need to be balanced at the lug holes, not the hub. Could that be the issue?

[RECHRGD]

Bent rear axle my bet ?

Wouldn't a bent axle just get worse the faster you went?  This thing starts at 65 and is over at 75.  I can cruise all day at 90 and be smooth as glass.  Bob

Problem solved!


pull a brake drum and look for odd wear patterns indicating a wobble in the axles, if you have one.  how about swapping tires front to rear, or trying another pair altogether?  it would be silly if you're chasing a radial pull with drivetrain parts. 

good luck!

You probably already now this but if your wheels are the two-piece reproductions, like most repro Magnums, they need to be balanced at the lug holes, not the hub. Could that be the issue?

I have run it up to speed without the tires and the vibration was still there.  I'll pull the drums today and check them out.  My driveshaft is with my driveline guy until early next week and I have some 2* shims on order too.  Being that the speed at which the vibration is present never changes regardless of where the pinion angle is set, I'm thinking I'm looking in the wrong area.  The axles are old originals, so maybe the drums will tell the story.  Thanks, Bob

[RECHRGD]

Well, I pulled the drums.  No uneven wear patterns, but one side had a lot more brake dust in it than the other.  When I get my driveshaft back I'll take it up to speed without the drums on and see what happens.  Bob

[bull]

Then it seems like it's got to be in the rear end. If not the axle or axles perhaps the diff itself. Is there any grinding noise associated with this or can you tell over the vibration?

Is the car dog-tracking at all, ie. rear axle housing at an angle? Even with everything balanced that could throw things off I would think.

[flyinlow]

Chased a vibration for months. Drove car with no fan belts (elastic band around water pump, I have electric fans and started with a cold engine)

Vibration gone....Bad alternator. New but out of balance.

Just an idea, dose not cost much.

I was sure my vibration was in the rear axle.

[bull]

Chased a vibration for months. Drove car with no fan belts (elastic band around water pump, I have electric fans and started with a cold engine)

Vibration gone....Bad alternator. New but out of balance.

Just an idea, dose not cost much.

I was sure my vibration was in the rear axle.

But he said the vibration went away when he tried it with the driveshaft out. That should have eliminated everything between the fan and the trans.

[flyinlow]

Not sure how he drove 70mph without a driveshaft.

If you towed it at 70mph was the engine running at the same speed it would normally run.

[RECHRGD]

Not sure how he drove 70mph without a driveshaft.

If you towed it at 70mph was the engine running at the same speed it would normally run.

The same way I drove at 70 without rear wheels.  With the rear of the car jacked up.   Bob