Sever driveline "Shakes".

[66dave284]

68' GT 350 Conv. (03372) - experiencing bad "swing-away" steering wheel/column shaking between 50/60 mph.  Old problem but getting progressively worse.  New Cooper tires on 10 spoke wheels.  Tires/wheels recently balanced and checked for out-of-round- twice!  Almost complete new front-end (brakes, calipers, rotors, bushings, tie rods, etc.  The front end rebuild has alignment has helped, but still cannot eliminate vibration/shaking.  Any help would be valuable.  Dave W

[davez]

Steering box could be worn out. In the 80s my 66 would hit bumps in the road causing the front wheels to chatter until I steered in to them causing them to settle down. You also have a rag joint at the base of the column. Check that.
dz

[CharlesTurner]

Shaking at specific speeds is usually wheel/tire related.  Steering box wear would normally cause sloppy/loose steering.

[jk66gt350]

Is it an automatic ?  About 10 years ago, my 70 Cougar vert automatic started doing the same thing starting at about 45 -55 miles an hour.  If I remember correctly, it wasn't constant, but came and went in fairly quick cycles.  Anyway after checking everything you have checked and more, it turned out to be a bad torque converter.  Something I had never before heard could cause that type of vibration.

[gt350shelb]

u joint or drive shaft

[mikeh]

Could be problem with the balance job/tire/wheel assy. Happens a lot! Not all balancers & mounting adapters are created equal! I would find a shop that has the proper adapters to center wheel on  balancer via lug nut holes(same as on the vehicle) vs center hole. Lug-centric balancing.

I would suggest that you go to www.hunter.com and click on the red "contact hunter" option in upper RH corner. This will give you the sales & service reps in your area. They should know what shops in your area have the proper equipment/technicians to diagnose your situation if it is indeed a tire/wheel problem.

Hope this helps, Mike

[Coralsnake]

Since its speed related I would guess its something that rotates in the driveline.

Personally attacking the smaller items like u joints would be the best strategy. Although uncommon you may have a driveshaft out of balance or even a bent axle.

[Bill]

Agree with Phil & Pete, I'd be looking at the U-joints.

Other areas to review:
Transmission & engine mounts
Front accessories bolted to the engine, crank pulley would be a good place to start.
Harmonics can travel throughout the chassis, which may have a similar "feel" for what you describe.
Then again, if you insist on it being rim/tire related, I'd be looking at the way the wheels are mounted to the car in relation to the lug nuts. A few times, I've seen where the holes in the rims where slightly hogged out (worn), enough to not allow for a firm fit to the lugs, no matter how tight you made the lug nuts.


Bill

[Coralsnake]

Oh wheel lugs...i once used 10 spoke wheel lugs on a steel rim. The car was on-a dolly.

Everytime I slowed down, the trailer and car pulled. When I did the safety check on day two each of the lugs was worn half way through. I was literally a few miles from having the wheels fall off

[pbf777]

Shaking at specific speeds is usually wheel/tire related. 

     +1 

Could be problem with the balance job/tire/wheel assy. Happens a lot! I would find a shop that has the proper adapters to center wheel on  balancer via lug nut holes(same as on the vehicle) vs center hole. Lug-centric balancing.

     Agreed, as I have had mostly negative experiences with the inability of the tire & wheel balancing efforts by the so-called experts over the years!   

     But do note that most O.E.M. wheel applications are "hub-centric";  though yes, most after-market wheels will be found to be of the so-called "lug-centric" system; though this is truly only accurate, or more importantly, only provides for proper fitment (registering) is if you are speaking of "10-hole (bolt/lug) Budd rims, generally as witnessed on older semi-trucks!   

     So what do you have?   

     Remember, that generally the rule-of-thumb is that if you feel the vibration in the seat, then it's emanating from behind you; if you feel the vibration more in the steering wheel, then it's coming from ahead of you.  Assuming that your drawing a appropriate conclusion in this initial observation?    

     Scott.

     

[Coralsnake]

I guess you could try some steel wheels and see what happens

[Royce Peterson]

Many of these cars got a vibration damper attached to the tailshaft of the C4 if they vibrated. Maybe this is one of them?

[gt350shelb]

also not uncommon if using stick on wheel weights for them to come off

[66dave284]

Some great comments .... Several ideas we have not addressed - but will shortly.  Steering box was replaced 5 or 6 yrs ago, but it sure demands checking out !!  Discount Tire is ordering 235/60 Goodrich T/A radials to replace the Cooper's (at no charge - how's that for good service).  Again, thanks for comments, very useful!!!  D 

[Side-Oilers]

Many of these cars got a vibration damper attached to the tailshaft of the C4 if they vibrated. Maybe this is one of them?

Yesteryear's engineering solution to a body vibration at speed: Hang a bunch of iron underneath (a la '61 Lincolns.)

Problem solved!