We’ve checked air pressure, balance and tread on all tires. had a mechanic inspect drive shaft,cv joints, and manually turn front wheels when car was on a lift - can’t find problem. Seems worse going uphill (under engine load).
Skier Bob, How Carefully Were The Tires Checked?
Was the car checked for defective Tire(s)? The tires need to be checked for radial and lateral run-out in case a belt has shifted. Usually this can be noticed at low speed and one can feel the car moving ever so slightly from side to side.
The wheel rims need to be checked for being “true”. A slightly bent rim will cause shaking and shimmy.
Balancing won’t remedy a situation as described involving faulty tire or rims.
Worn out struts will magnify any imperfections in the suspension/steering system.
Has the harmonic balancer on the engine been checked? The “worse going uphill (under engine load)” makes this a possible candidate.
CSA
Maybe this is an engine performance problem and is not related to the wheels, suspension, or drive train at all.
Weak fuel pump, clogged fuel filter, partially clogged catalytic converter, weak cylinder due to low compression, etc, etc.
As to CV joints, checking them while they’re installed in the car is not always a reliable method. It’s entirely possible for joints to feel perfectly tight with no slop at all but they may have odd wear patterns in the bearing races that can cause binding. This binding can cause a shimmy.
The only reliable way of checking them is by removal and checking them on the workbench; providing one knows what to look for.
Of course if you’re going as far as removal then you might as well replace them.