Bad vibration at 70-mph

[64studeavanti]

I hope you all can help. I have a 64 avanti R1 4sp 3.37 TT. It has rebuilt kingpins, all new bushings (installed correctly), new shocks, new 205R75 15 tires on new 15x6 Ford Magnum rims (vintique repros), new U joints and rebuilt transmission. I also had the wheels aligned when the front end was rebuilt (I had them set the toe to 0 to account for the radials) and of course the tires were balanced. I have a severe vibration at 70mph. It seems to be present a little at all speeds, but I dare not go on the freeway. I don't believe that it is engine related as I can put it in neutral with the same results. Neither the rear drums or the front rotors seem abnormally hot. The car tracks true without any pulling. When replacing the U joints, I noticed some slop in the rear end. Any Ideas?

[Milaca]

Did you have this vibration before performing these repairs? Perhaps a balance weight fell off the driveshaft? Just a wild guess. You could jack up the rear of the car and place jack stands under the rearend, then start the car and put it in gear and rev up the engine. If it vibrates, then it is something back there causing the problem.


Brent's rootbeer racer.
MN iron ore...it does your body good.

[Chucks Stude]

Be more inclined to think that one of the needle bearings in the u-joints fell into the cup. Had that happen once, and drove me nuts trying to find it. The next thing to look at, is the play in the rear bearing of the transmission. They keep telling me that if it is really bad at 70, only, that it is the tires, maybe a bad belt? Just some thoughts. Others will chime in.

[jclary]

Another thing to check is for a warped rim. Radially and laterally. You can do this with a magnetic base dial indicator. I once had a warped brake drum drive me nuts until I found that it was warped. With your Avanti it could be a wheel, hub, or disc. A bearing race not completely seated could cause it as well. Hope you find it soon. I know how frustrating that can be especially after all the work you have already done.

[64studeavanti]

Thanks for the quick replies. I just put new joints on today - taking special care to ensure that all the bearings are in place. When the transmission was rebuilt, all the bearings and bushings were replaced. The tires are new as are the rims. I will still check them though. The drive shaft is original and could be the problem. The weights appear to be in place. I'll keep plugging away. Something will make sense soon.

[dpson]

From my days of selling tires at Sears; vibration starting around 65 mpg is most often due to tire balancing issues. If it is felt in the hands its front tires; in the seat its the rear tires. Hope that helps.

Dan Peterson
Montpelier, VT
1960 Lark V-8 Convertible
1960 Lark V-8 Convertible (parts car)
1961 Lark Crusier
1962 Lark V-8 Regal Convertible

[HookedonStudies]

I agree - check the tires. You may have just lost a wheel weight.

Pat Casey
55 Commander
58 Transtar
62 GT Hawk
66 Cruiser
SDC Member since 1983

[DEEPNHOCK]

Spin balance the tires again....

Does the shake change if a gentle arc turn is held?

I still like a lil' bit of toe in....

[Gunslinger]

As already mentioned, do you feel the vibration through the steering wheel or through the floor? If through the steering it's from the front...if through the floor it's the rear.

Even if you have the tire/wheel combinations balanced, you could have an out of round tire or rim. There's no such thing as a perfectly round tire or a perfectly round rim...they all have a high spot, but as long as the dimensions are kept with specs, they present no issues. Sometimes the high spot on a tire gets mounted directly over the high spot on the rim and it magnifies the out of round condition. Determine which tire and rim and have the tire broken down and rotated on the rim and the problem will usually go away. Otherwise the tire or rim has to be replaced.




Poet...Mystic...Soldier of Fortune. As always...self-absorbed, adversarial, cocky and in general a malcontent.

[63t-cab]

Very unlikely,but I had a bad vibration some time ago and it was a bent rear axle shaft.

Joseph R. Zeiger

[Milaca]

I had a bent rear axle on my Hawk, but didnt notice any vibration. I wouldnt have known it was bent had it not been for the wheel wobble.


Brent's rootbeer racer.
MN iron ore...it does your body good.

[bige]

Don't assume the wheels were balanced properly I've had the occasion twice where the balancing was just done wrong. That being said you will feel a badly balanced wheel through the steering wheel or in a wiggle from the rear as others have pointed out.

If the vibration resonates through the entire car it's likely in the driveline. The U joints come to mind first, if the yoke wasn't marked and assembled in a different spot than when the shaft was originally balanced it could throw things off. The play in the rear is normal however you may want to make sure the yoke on the differential is not loose. Push up and down on the driveshaft at the very rear to check the rear yoke and as far forward as you can to check the tailshaft bushing in the trans. If you detect up and down movement chances are that's your vibration.

ErnieR






Best so far 15.065 @ 91.84 MPH Island Dragway Great Meadows NJ Summer 2009.

[64studeavanti]

I'll try several of these this weekend and let you know what I find. It's hard to tell where the vibration is coming from. the steering wheel doesn't seem to vibrate much so I'm leaning toward the driveline. I did mark the yoke and shaft when I put the new joints in - but who knows what the PO did. Again thanks for all the suggestions.

[sweetolbob]

Just for the record.

If you exhaust all the possibilities of tires, etc. and want the drive shaft balanced, locally (Michigan)it's $50. I just found that price today when I dropped of my Avanti shaft for upgrading.

Bob

,

[Clem64]

Only being able to diagnose your vib problem just by a verbal description is tough. Vibration somewhat similar to what you describe that I have experienced, was ultimately caused by worn transmission and engine mounts. If yours are tired, I would suggest installing new mounts as part of your search for the causes of the problem.

Dean




CLEM DESEE MISTY