Help with shaking?
 

I haev a 1980 911SC w/ 117k miles. I get a vibration in the steering wheel at highway speed and it is most noticeable at 70MPH. If I go fatser it begins to subside but does nto go away completely. Periodically it will smooth out completely but only for a few seconds and then starts up again. If I grip the wheel real tight I can almost stop t from shaking.

I just replaced my ball joints because I thought that might be the problem but it seems like it only made it shake faster. I assume becasue the ball joints were worn or bad so I was not getting as much feedback from them as the new ones.

On my BMW it was the Idler arm which was a $20 fix but this car does not seem to have an idler arm.

Any suggestions?

Wheels need balanced? Did you shake off a wheel weight?

How old are your tires?

Tires and wheels are new. I was thinking maybe it was jsut the tires that need balancing.

It's possible. You had the wheels/tires balanced together when installed, right? There could be a defect in the tire, or a bad balancing job, or a wheel weight has come off, or maybe something else, like an out of balance brake rotor, a bad shock, or worn stering or suspension components. Alignment is also a possibility, but usually the symptoms don't change as the speed increases. Check your air pressures while you're at it.

The tires were mounted and balanced by the PO.

Has it been sitting for a lengthy time? with todays softer high performance tires, they are easier to flat spot.

Wheels shake
 

My 2 cents, I'm not a mechanic and don't know much about these cars but I had the same issue when I bought my 76-930 but thru a PPI inspection the mechanic told me about the violant shake and the need to change the front shocks. I did experience the same when I received the car driving at higher speeds. the car would shake pretty bad.

You have a 1980 with 117000 miles, my car has only 12,000 miles but the years of sitting erroted the shocks. have them checked, might be the problem for you I ended up upgrading mine to balestin sport shocks and changed all 4 now drives awsome.

Good Luck

Re-check the tires (balance and roundness) and check the wheels for trueness. Vibration over 65 is generally generated at the rear of the car.

a beer usually helps my shaking.

Alignment cured my steering wheel shakes when I first bough the car 1 1/2 years ago.

A vibration that you can drive thru usually indicates a balance problem. A flat spotted tire you can feel the vibration or thumping get progessively faster as you accelerate. Check wheel bearing adjustment, especially if vibration goes away if you slightly turn wheel. Checking for tire balance and roundness would be the simplest place to start. Rebalance should only set you back $10 per tire.