My car has a droning vibration that starts around 65 mph. At 55 it's fine and as I approach 70 it gets worse. The vibration oscillates on regular intervals, unless I put the car in neutral, and then it's a constant (and worse) vibration until I put it back in drive.

Over the past 8 years I've replaced the universal joints, transmission, brakes, wheels, and I've had the tires "computer spin balanced" multiple times. The vibration has not been affected by any of those changes.

How do you diagnose something like this?

I think I'll get the driveshaft balanced. What would you do to troubleshoot the rear axles and differential?

Any other ideas?

Lee Entrenger (Mushroombert) didn't think this vibration was all that bad when he drove my car last summer. But I sure was jealous when I drove his Challenger and it was smooth as glass at speed.

My father had this with his old GTO and it did turn out to be the drive shaft. Look carefully at it and see if it has thrown it's original balancing weight from the factory. Should be a weight about an inch long.

the auto and manual trans has a bushing( like a bearing) inside the tail of the trans where the drive shaft mates to the trans and this bushing helps keep it from vibrating. if it's wore out, there will be a vibration at high speeds.

68 400 all #matching 4 spd to go

Do you mean the rear transmission seal? I put a new one in when I switched to a TH-350.

When I replaced the universal joints I cleaned the drive shaft and there was a counter weight on it. I'm not confident it is in the same orientation that it was in before - if that matters.

That being the case, take the driveshaft out and turn it 180 degrees in the rear pinion yoke and drive it again. It would be a good idea to have the shaft balanced while its out of the car.

I will. Flipping the driveshaft 180 degrees is free, so that's a good test.

Thinking some more about ho4spdtogo's advice. If he's talking about a bushing inside the tailshaft, I reused the ST-300 tailshaft on my TH-350. That would explain why there was no change in the vibration when I changed the transmission.

I had that at about 65-70 a few yrs ago...had the drive shaft balanced ...went way

Thanks guys. I'll try to rotate it this weekend. If that doesn't work, I'll get it balanced.

I had a similar problem, mine turned out to be a slightly bent rear axle.

John, Where in Wisco are you? South East? I know a great driveshaft guy in Elkhorn, Wisconsin. Elkhorn Driveshafts.

Sometimes it could cost more to balance an old one than to make a new one. I had a new one built by this guy with new yokes to the exact size I needed when I changed out my rear end. He's a very honest nice guy, and will tell you straight up.

no. there is a sleeve inside the tail housing. if you remve the seal there is a sleeve or bushing pressed into the housing it serves to support the shaft an helps to keep it in place. this part is mostly neglected because you dont see it and does wear out. it will cause a vibration. if you done the rest then that the pup.

68 400 h.o 4 spd to go

4dabird - I'm in the Green Bay area.
ho4spdtogo - I'll look for a different tailshaft housing if the driveshaft troubleshooting doesn't work out.
derding - I hope it's not a bent axle. I didn't want to get into the rear end this year. But, that's last on the list.

Thanks.

I too am having the same problem as "RossettiJ" the vibration starts about 65 to 70, I've changed out the u-joints,had the drive line balanced, changed out the bushing in tail shaft, tried different yokes, check the pinion,tires balancec??

The rear end is 12 bolt with 3.08 gears, hows does one check for a bent axel shaft? If you have a bent axel would it not vibrate at all speads? Could a wheel bearing be bad?

1968 Firebird Coupe

Vibration analysis. I used to do it at GM for preventitive maintainance. I had a hand-held reader with a wand that read the vibration. Download to a computer and it told the frequency among other qualities of the vibration. Once you have the frequency you could tell what was vibrating. The frequency matchs the revs of what is vibrating. You can do this to an extent with your senses. Try to distinguish the cycle of the vibration and it will give you a clue.

Huh? Sorry Jim, my a$$ isn'calibrated to match that vibration up with say, the left rear axle bearing.

I called around and having the driveshaft balanced is only $61.00.

You wouldn't 'feel' an axle bearing much. The drive shaft you will feel and the dash would probably shake too.

yes, a wheel bearing could be the problem. if everything that can be done, has been done to the drive train; then, it is possible the engine might be the problem. its a long shot; but, either compression or the main bearings could be worn out. or maybe the flywheel or tourque converter are slightly out of balence or the attaching bolts are not balenced. possibly the pilot bearing is worn out. just some ideas.

68 numbers matching 400 h.o 4spd to go.

Mine would start right around 60 mph and get worse the faster I went. I tried everything including balancing the drive shaft. I too have a 12 bolt, so I opened it up, removed the c-clips and brought both axle shafts in to a drive line shop. They spun it with a dial gauge right on where the bearing normally sits. Turns out the passenger side was WAY out of spec. Bought a new axle and the problem is now gone.

A more serious response to Fbody69's idea:
The vibration is an oscillation like a sine wave. The amplitude gets greater as the speed goes above 65 or so. The wavelength however is longer than the rotation of the wheels, driveshaft, u-joints, bearings, engine, etc. It has to be a resonant frequency of some sort. So I really couldn't guess what it is that way.

One interesting clue that I don't know what to make of, is that the oscillation changes when I put the car in neutral. The wavelength gets much shorter. It must be changing because the driveline is unloaded, but it's still there because of the vehicle speed and not engine RPM.

I'm on the west coast right now so I can't do anything until this weekend.

Okay, professional vibration analysis guy. What do you think of them apples?

AHHH Now you are talking John! I would guess, by your description, that your problem is internal in your differential. It's a good chance that you have a problem with a main differential bearing or an axel bearing. I had exactly what you are describing in one of my trucks... It was the main diff bearing. It allowed the diff to move a small amount and vibrate. It always sounded different when I shifted it into neutral.... The pressure is off allowing it to rattle at a different frequency.

Just an update on an old thread. I finally solved my vibration problem over the winter. It was Bjorn's suggestion that was the winner. I had the drive shaft balanced. I drove the car for the first time yesterday and it was smooth as a baby's butt all the way up to 85 mph. I've been pulled over too recently to go any faster or for any longer. But what an improvement! Thanks Bjorn.

Thought it would be John! I had a van like that too...had the shaft balanced and gone....

Bet that feels better!

great , thanks for the update....looks like I get a few right, once in awhile!
if you throw spaghetti on the wall enough ,some will stick...lol


yeah , it sounded just like what I went thru 5 yrs ago.....

Thats great news, John. Glad you didn't dig into the rear end as advised. That would have been a mess!

And cubic dollars!

Had the SAME problem with the 67..Was a bad driveshaft.