# Finding bad bad vibrations



## [email protected] (Nov 24, 2008)

Car vibrates above 55 mph. Front wheels and steering are steady. Vibration is coming through the body. I have balanced all wheels, replaced u-joints, balanced the drive shaft. 67 GTO, 400 auto with 3:23 posi, all original running gear. Torque conv was replaced years ago. The rest is original stock. Any suggestions?


----------



## Rukee (Feb 8, 2007)

Welcome to the forums.
Do you have uni-lug wheels or whatever they are called?


----------



## Too Many Projects (Nov 15, 2008)

Basic questions......does it follow vehicle speed or engine rpm i.e. if you go into a lower gear when it starts vibrating, does it change. Does it change when applying power or letting up and coasting. Is there any noise that accompanies it ? 
My first idea is that the harmonic balancer may have slipped due to the rubber isolator being old. It may be hard to see a change, but a timing light will show the mark to be way off. After that a balance weight may have come off the flex plate. Any change in the way the transmission acts/shifts that could indicate a problem in it or the torque converter ?


----------



## 68_Goat (Nov 7, 2008)

Might take a look at the rear tires..do they run true? An out of round tire can be balanced, but is still out of round and will hop. Flat spots, twisted belts, bent rim(s), etc.


----------



## Eric Animal (Oct 28, 2007)

Broken belt in a rear tire??


----------



## VettenGoat (Jun 19, 2007)

Try isolating the vibration first. With the car in neutral, run it up to highway RPM. (Since its an auto matic, try it in park also and see if there is a difference) If it is still vibrating without moving, then the harmonic balancer is a good place to start as TMP suggested. It sounds like you've replaced a lot of the usual suspects, but what condition are the mounts and in particular the transmission mount in? For the cost, its worth replacing them. You can try the tranny mount first (its easiest and most questionable), but do them all if possible. Check the obvious crossmember bolts too. Also, though less likely, I've also had exhaust flanges loosen up on me and vibrate a bit, but they'll usually tell you if they're loose. Good luck and happy hunting//Mike


----------



## Rukee (Feb 8, 2007)

Too Many Projects said:


> Basic questions......does it follow vehicle speed or engine rpm i.e. if you go into a lower gear when it starts vibrating, does it change. Does it change when applying power or letting up and coasting. Is there any noise that accompanies it ?
> My first idea is that the harmonic balancer may have slipped due to the rubber isolator being old. It may be hard to see a change, but a timing light will show the mark to be way off. After that a balance weight may have come off the flex plate. Any change in the way the transmission acts/shifts that could indicate a problem in it or the torque converter ?



Those are good ideas and both would be engine RPM related. Popping the tranny into neutral and the vibration should go away if it's either of those two things.
I'm kinda leaning towards a bent rear axle maybe? Or an out of center rear wheel. That would be speed related, but not engine RPM related.


----------



## Too Many Projects (Nov 15, 2008)

I like to start simple. He stated the wheels had been recently balanced. That SHOULD temporarily rule out a bent wheel or broken belts or out of round condition of the tires. I'll assume the person doing the work would've noticed this and are good, for now. New u-joints and balanced driveshaft means someone had this out but as VettenGoat points out may not have noticed a collapsed trans mount. Good call on his part. That is why I asked if he noticed any new/odd/loud noise associated with this vibration. A collapsed trans mount will transfer a lot of "mechanical" noise to the car along with the vibration. 
After 25 years in the repair field, I have heard a lot of stories about noises and vibrations. My favorite is still the guy back in the early 80's that drove his Chev into our facility and said "I was driving along and it starting making a TICKING noise and when that went away I noticed a vibration It's been a way since I had a tune-up". I went out to the lot and started it.........yes it vibrated badly, in fact it felt like a dead cylinder. I pulled it in the bay and opened the hood and checked for the obvious plug wire off, vacuum hoses...etc. That's when I noticed oil on the left frame rail and got curious. I set the pads, raised the car and almost fell on the floor in hysterical laughter. #5 rod was sticking out of the block at the pan flange after nearly sawing the block in half almost to the head. It held enough oil to keep pressure and run. I walked into the customer area and tried to tell him (with a straight face) that I had found the source of his TICKING and would he like a quote on a replacement engine.........:rofl:


----------



## 68_Goat (Nov 7, 2008)

The reason I'd mentioned an out of round condition, even though he'd said he had them balanced, is that I recently bought new tires. I agree with you that they should have caught it. The "tech" doing my tires didn't catch the tire running out > 1/4" on the od, and slammed it on my truck! Needless to say, I brought it back promptly, and found the problem.


----------



## Too Many Projects (Nov 15, 2008)

68_Goat said:


> The reason I'd mentioned an out of round condition, even though he'd said he had them balanced, is that I recently bought new tires. I agree with you that they should have caught it. The "tech" doing my tires didn't catch the tire running out > 1/4" on the od, and slammed it on my truck! Needless to say, I brought it back promptly, and found the problem.


Exactly why I don't rule anything out completely either.

Amazing how a kid working for minimum wage throwing tires on wheels becomes a "Technician" and doesn't know enough or pay attention to obvious defects...........

It would be nice to hear back from the originator of this thread whether he has had a chance to check into this further. All this speculation and no answers...........:willy:


----------



## J.E.T. (Sep 30, 2005)

Tires first...........mounts (motor and tranny) second. That should cover it.

JET


----------



## Tri-Power (Jan 10, 2008)

I bet i know. When I first got done with my frame off I left the rear differential alone. I didn't even check for proper backlash. Anyways, I had an extremely similar vibration. Anything above 60mph was a pretty serious vibration. After driving it a while, I noticed that the vibration was significantly decreased under moderate to heavy acceleration (you should check that). And the vibration was severely amplified when i was "rev-matching" at that speed (in gear, but holding the engine RPM to a coast speed. (neither engine braking or accelerating)). Anyways, it ended up being play (backlash) between the ring gear and carrier. If i had to guess I'd say that is your problem. Properly rebuilding my diff fixed my vibration.


----------

