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

[Just 6T9 CHGR]

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?

Did that to mine & I still have my vibration.....feeling your pain Bob

[Tom Q]

Have you pulled the rear axles & checked the bearings, regreased the bearings and set the end play at 0.003-0.005???
Don't be surprised if the vibes are coming from the pinion bearing... 

[greenpigs]

Do you have green bearings on your axle shafts? I have heard those can go bad.

[RECHRGD]

No green bearings and the end play is dead on.  The wheel bearings have about 25K miles on them and no, I haven't looked at them yet.  I can turn the pinion yoke very easily by hand without the brake drums in place and it's smooth as glass.  No resistance at all.  Before I start tearing into more things, when I get the driveshaft back, I'll have the wife run the car up to speed with it in the air.  If the vibration is still there with the brake drums removed, I'll physically "feel" the rear end and the tranny/GV unit and see if I can detect where the source of the problem is.  I promise to be CAREFUL under there.   Bob

[greenpigs]

You sure the driveshafts guys equipment is operating correctly?

[dpixel]

Usually driveshaft vibration problems are at lower speeds.  I had a bad shake at 15 to 20 mph when I changed out my tranny mount.  Had the driveshaft rebalanced and new yoke(yoke was junk).  
I would suspect the wheel/tires.  I'm not sure how fast the balancers go, probably not 70.  Maybe for the hell of it try an old set of wheels and tires.  

Also, aren't the drums balanced at one point (if you have drums still).  I recall a little weight on my '72 rears.

[RECHRGD]

Well, the driveline guy is the best in town.  All the hot rodders and commercial outfits use him.  Last year he spent most of a day screwing with this thing and didn't even charge me because he couldn't fix it.  Different wheels and tires won't change anything, as it still vibrates without wheels and tires on the car.  We'll try it without the drums as soon as I get the driveshaft back.  Thanks, Bob

[bull]

Take your cell phone off vibrate next time you test it too.

[RECHRGD]

Take your cell phone off vibrate next time you test it too.

Well now you've got me wondering.  Naaa couldn't be, could it?

[bull]

Take your cell phone off vibrate next time you test it too.

Well now you've got me wondering.  Naaa couldn't be, could it?

[motorcitydak]

Just to throw this out there...When my truck hits the same speen you are talking about (65-70) I get a few vibrations. 1 of em is my tires. They are 35x12.50 Mickey Thompson MTZ's and have a few bites taken out of the thread from various off road objects. The other one is caused by my exhaust note. It just so happens to hit the correct resonate frequency and makes my shifter knob (Lokar) vibrate like crazy. It is loud and sounds like something is about to fall apart. It goes away when I touch the button on it and dampen its movement.

You may want to consider that as a possibility. Your exhaust note may be causing something to vibrate. Since you said that the harder you are on the throttle, the more violent it sounds but if you let off it, it goes away. Same thing here, I just know what is making that noise and keep forgetting to contact Lokar for a new shift knob. I have no idea what is causing yours obviously. It could be a window vibrating thru a worn out seal, or a screw coming loose and letting the parts it is holding shake. If this is the case, running the car in the driveway on jack stands will most likely not bring out the noise because the motor is not actually working very hard to spin the tires. You would have to be able to apply the brakes to the same degree of resistance as the car feels when it is pushing itself at 65-70. The best way to help here is to have someone else in the car and compare notes on where you are hearing the noise from. You may just be hearing it coming from behind or under you. Put someone in the back seat and see what they have to say. If you can stomach it, have that person drive the car while you search around the car to see if you can get closer to it.

I have noticed that if you are describing a particular problem to a person with a specific specialty, they will tell you what they think that is relevant to their position. A driveshaft guy will say it may be a u joint. An axle guy can say it is the axle bearing. 

[RECHRGD]

Just to throw this out there...When my truck hits the same speen you are talking about (65-70) I get a few vibrations. 1 of em is my tires. They are 35x12.50 Mickey Thompson MTZ's and have a few bites taken out of the thread from various off road objects. The other one is caused by my exhaust note. It just so happens to hit the correct resonate frequency and makes my shifter knob (Lokar) vibrate like crazy. It is loud and sounds like something is about to fall apart. It goes away when I touch the button on it and dampen its movement.

You may want to consider that as a possibility. Your exhaust note may be causing something to vibrate. Since you said that the harder you are on the throttle, the more violent it sounds but if you let off it, it goes away. Same thing here, I just know what is making that noise and keep forgetting to contact Lokar for a new shift knob. I have no idea what is causing yours obviously. It could be a window vibrating thru a worn out seal, or a screw coming loose and letting the parts it is holding shake. If this is the case, running the car in the driveway on jack stands will most likely not bring out the noise because the motor is not actually working very hard to spin the tires. You would have to be able to apply the brakes to the same degree of resistance as the car feels when it is pushing itself at 65-70. The best way to help here is to have someone else in the car and compare notes on where you are hearing the noise from. You may just be hearing it coming from behind or under you. Put someone in the back seat and see what they have to say. If you can stomach it, have that person drive the car while you search around the car to see if you can get closer to it.

I have noticed that if you are describing a particular problem to a person with a specific specialty, they will tell you what they think that is relevant to their position. A driveshaft guy will say it may be a u joint. An axle guy can say it is the axle bearing. 

Thanks for the input motorcitydak.  There is really no "noise" associated with this.  You definitely FEEL it in you butt and SEE it in the fuzzy rearview mirror.  Passengers in the car feel the same thing.  The testing while jacked up on the lift seems to bring on the same symptoms at the same speeds.  Although I cannot duplicate the increased vibes under load, I still can feel the vibrations at the same indicated speeds that I feel on the road.  Anyway, I'll get the driveshaft back today and try it without the drums on.  I'll also check for loose stuff that could be causing any harmonics.  Bob

[RECHRGD]

This is still driving me nuts.   I took the rear drums off and it got much better, but the vib was still there.  That made me think that maybe a wheel bearing was going out, so I pulled both axles out and ran it up to speed.  It got a little better yet, but still there.  Tried another pinion angle and no change.  Now, with less rotation mass going on I found the the vib does, in fact, change when I shift into overdrive.  So maybe it's rpm related rather than driveshaft speed.  It seems to come on at around 2800rpm which is 68mph or around 80+ in overdrive.  I put my wife in the car and ran the lift up in the air.  I had her run it up to the vibration point while I "felt" things with a wooden dowel.  I could feel the vibration pretty much everywhere, but it was at it's most pronounced at the output shaft of the G/V.  If it wasn't for the fact that it seems to be more engine rpm related now, I would think it's the G/V unit itself, but now I'm not so sure.  I also noticed that the engine is sitting almost 2* down toward the passenger side of the car.  I've noticed this before, but just thought it is to compensate for the engine torque.  BTW, these are the new engine mounts that were installed to try and tone down the vibs with the schumaker mounts.  Anyway, I think I'll pull the G/V unit tomorrow and put it all back together.  Pray for me!  This is getting very old.    Bob

[bull]

You said before that the vibration went away when the driveline was out, right? My guess is that something gets goofy with the GV when you install the driveline in it. Or, it's something in the differential instead of the axles. Is it possible that the GV is fine until you put a load on it?

[RECHRGD]

You said before that the vibration went away when the driveline was out, right? My guess is that something gets goofy with the GV when you install the driveline in it. Or, it's something in the differential instead of the axles. Is it possible that the GV is fine until you put a load on it?

I'm now thinking that, because of all the driveline rotating mass that a small vibration was being magnified when doing earlier tests.  The difference between having the driveshaft installed and not may have been so great that I may have thought there was no vibration w/o the driveshaft when there may have well been some.  Bob

[bull]

If that's not it I'd take a good look at the differential. Anyway, I hope you figure it out.

[RD]

just my two cents, but:

no matter how you may balance a engine assembly, there will always be either a certain rpm, rpm range, or speed in which you will fill a certain amount of vibration as nothing is PERFECTLY BALANCED.

is your engine internally balanced?  If it is, drop the trans and check the endplay on your crankshaft.  Secondly, replace the converter with a neutrally balanced converter when reinstalling.  I know its a pain to do this, but start at the front and work your way back.

[RECHRGD]

I pulled the G/V and tailpiece this afternoon.  The only thing that I saw that may be suspect is the solid coupler that attaches the tranny output shaft to the input shaft of the G/V unit.  With the coupler bottomed into the G/V there is enough slop to create about a 1/8" movement on the free end of the coupler.  There is no slop on the tranny end of the coupler.  I'll call G/V on Monday to see what tolerance they want to see.  Bob

[tan top]

I pulled the G/V and tailpiece this afternoon.  The only thing that I saw that may be suspect is the solid coupler that attaches the tranny output shaft to the input shaft of the G/V unit.  With the coupler bottomed into the G/V there is enough slop to create about a 1/8" movement on the free end of the coupler.  There is no slop on the tranny end of the coupler.  I'll call G/V on Monday to see what tolerance they want to see.  Bob

  good bit of dective work    .......

[bull]

I'd say 1/8" is too much play; definitely enough to make a wobble. I hope that's it. It sucks when there's a problem with a car but what sucks even more is not being able to figure out what the problem is. I'd rather be able to figure out a $1,000 problem than to be perpetually stumped by a $2 problem.

[RECHRGD]

Well, I talked to Mike at G/V and he did not think that the coupler could be the problem.  He said that even though there may be some slop in the fitment, it would tighten up under power and cause less rather than more vibration.  OK, I guess I can buy that.  So, I just went ahead and yanked the thing out and put back the old tailpiece and driveshaft.  Guess what??  No more vibration!!!!!!  So, If it's not the coupler then something is goofy in the unit.  I'm waiting for a call back from Mike as I type this.  For now all I have is a $2,600.00 vibrator.   Bob

[GPULLER]

I don't buy the 1/8 of slop theory.  If that was true wouldn't u-joints be OK if they had 1/8' of play???  Don't think so...

[lisiecki1]

Well, I talked to Mike at G/V and he did not think that the coupler could be the problem.  He said that even though there may be some slop in the fitment, it would tighten up under power and cause less rather than more vibration.  OK, I guess I can buy that.  So, I just went ahead and yanked the thing out and put back the old tailpiece and driveshaft.  Guess what??  No more vibration!!!!!!  So, If it's not the coupler then something is goofy in the unit.  I'm waiting for a call back from Mike as I type this.  For now all I have is a $2,600.00 vibrator.   Bob

Glad you've got it narrowed down, please keep us updated 

[tan top]

got it pinpointed  then !! is the GV unit !! at least you know what it is now !!

[RECHRGD]

I just talked to Mike and he's stumped.  He told me to box it up and send it to them to check out.  He said they've never had a unit that was the cause of customer's vibration problems, so this should be interesting.  He's not being an ***hole about it, but just seems to be in denial.  I'll let you know what happens, but it will most likely take awhile.  Bob