I have an issue with my '70 convertible. Around town, between about 20 and 40 mph there is a "shimmy" from the front end. I don't feel anything through the steering wheel. On exceptionally smooth roads or at higher speeds it goes away. I'm pretty sure the problem has not gotten any worse or better since I got new tires and wheels.

The only work that's been done on the front end since I've owned the car is new upper ball joints. I was reading on a Chevelle forum that this symptom is associated with worn LOWER ball joints.

I'm tempted to take it to a shop and have the control arm bushings and lower ball joints done and shocks too.

Anybody have a similar issue that they ended up solving?

 

Interesting that you replaced the upper ball joints. My experience is the lowers wear out 2-1 compared to uppers and last about 75K miles.

You can check the lower ball joints by putting a floor jack under the lower control arm and lifting the wheel a couple inches off the ground. Then use a long pry bar under the tire and try to pick up the wheel and look for slop in the joint. It should have no more that .035 in.

While you have the one wheel off the ground try to move it side to side to check for slop in the tie rods. The bushings are just a visual inspection to see if the rubber is still intact.

A couple of the guys have posted front end rebuild threads if you want to see how it's done.

 

You may want to swap the front and rear tires, just to eliminate tires and wheels from the equasion. I have had tires that cause a wobble at under 40.

 

You sure it isn't cowl shake?
My '68 GTO convertible twists and shimmies like crazy at those speeds on rough roads. I've gotten so used to it I hardly notice it anymore

"Cowl shake is the term used for the phenomenon experienced in many convertible or open top automobiles where, due to lower structural rigidity caused by the lack of a roof, the middle section of the chassis flexes, causing the bulkhead in front of the passenger compartment to move and vibrate when the vehicle is subject to uneven road surfaces. Passengers feel it as a noticeable vibration and shudder."

 

There is definitely an element of cowl shake but this is occuring on normal city streets, not ones that are particularly rough. My '68 Firebird convertible used to get a case of cowl shake going over railroad tracks and things like that.

I'm thinking it was upper ball joints because that's what the shop recommended while I had them working on another issue. But I'll have to check. I did not realize that the lower ball joints wore out faster. If the lowers haven't been done that could be the issue since I have 74,000 miles on the car. Thanks for the tips Highwayman and everybody.

 

It's quite east to diagnose front end troubles.
Grab an a helper and jack up the front end.
Have the helper mover the wheel back and forth,up and down,and watch the play.
You will easily see where the front end parts are flexing.
There should be zero play with new components..at least none that will be able to be seen with human strength.

 

I have a cowl shake all new front end including springs and tubular control arms,new front end alignment,new tires and cragars.New sway bar bushings,new fast ratio steering box.Had the wheels centered and balanced and still have a shake at 40mph dont know about the highway havnt tried that yet.New tubular rears as well.All my bushings were wore out on the ld ones so i figured this was going to be a big improvment.Almost plling my hair out after spending all that money and time to have the same shake.The only thing i havn't replaced is the tail lights lol.Anyone have any tips?

 

Do you feel it in the steering or the seat?

 

Little of both

 

I don't think anybody has mentioned an idler arm. Years ago I had a 74 chevy pickup do this and it was the idler arm. This is also the cheapest and easiest thing to change.

 

As stated above wear part problems can be eliminated with careful inspection of each individual piece. There is no guess work. Lower control arms, idler arms, tie rods etc are worn you can tell. Rotational out of balance problems are harder to identify. Typically front end components that are worn you feel more in the wheel than in the seat or floorboard. Rotational problems can be identified with a methodical approach as well. I would first have all 4 wheels and tires balanced. If the problem is still present I would jack up the car at each corner and rotate the wheel to check for wobble or a bent wheel. Then I would jack the rear of the car up and place on jack stands. Put the car in gear and see if you still feel the vibration. This would eliminate the front end all together and point to a driveline issue such as driveshaft or u joint problem.