My 1987 S4 seems to want to drift out a bit on the back end. I'll be picking up some almost new tires from Fred in another couple weeks and, maybe that will take care of it since the rear tires are in need of replacement - not bald but almost.

My question: At 77 years old, I don't drive very fast but here in Wyoming, with a lot of twisty mountain roads, should I expect this kind of behavior or should I look at the rear suspension? The weisach axel was supposed to be great for cornering.

 

If youre almost bald..youre no longer running on good rubber layer/type that the tread had..plus its harder more dried out now..etc..etc.

 

These cars are great and very predictable in the twisties. Get some decent tires on there and see if you still have any problems. There may be other issues, but you already know that the tires are bad, so start there and see if it doesn't take care of it for you.

 

the bushings that seem to have the greatest effect on rear handling at the ones that connect the lower control arm rear link to the rear cross member,
you will know these are bad when you can let off of a full throttle acceleration and you will feel the rear steering itself one way or the other, fitting new bushings is a job but it will transform the rear to a predictable state,

same goes for fitting new shocks , these have an immediate effect on ride quality and performance

 

Check the large bolt thru the bottom of the shock and upright on each side. If it is at all loose, or if the large spherical washers are not properly installed, the upright can move enough to steer the rear end.

 

My first thought as well.

Jack each rear wheel up and work the wheel side-to-side. It may be stiff when on the ground.

 

Definitely tires. Both of my 928's handle like there on rails. Takes a lot to get them to kick out. You must have a limited slip diff?

 

The ONLY time the rearend should step out on a 928 is power oversteer where YOU are hard on the gas and the rearend drifts out in a corner, otherwise something is wrong and probably more than just tires.

 

Check torque of FRONT lower A-Arm mounts.

Had a pair back-out. On a long right sweeper we thought the rear of the car was going to come around and pass us. Problem was the front left A-Arm was about to fall of.

Easy fix, but dangerous situation.

 

I agree.

But cap rubber where the tread is at..is useful.

UNDER that on many tires, the rubber left is useLESS and may as well be hard plastic on some surfaces.


On the low-noise and porous asphalt laid down on Hwy9, Santa Cruz County...I can tell the day Ive lost just enough "good cap" off my tread and Ive worn down to the cushion/gum layer subtread...which..again, is total **** for grip.

 

Check your tire pressures first. The rear end is very sensitive to side-to-side differences in pressure.

 

Under mild driving, which is what the OP describes as his method, tire condition should not leave you feeling like the rear end is steering away from the line.

I'd make damn sure the suspension, front and back, is solid before tackling any twisties.

 

MY mild driving...has passengers looking for handholds.

 

Having gone from bald rears to new Dunlops, there is a huge difference in grip levels.

The other thing you should do after new tires is drive it until the suspension has settled, then once its settled, get a proper 4-wheel alignment by a shop familiar with aligning 928's (so that they don't lift the car and unsettle the suspension again).

Unlike other cars, you can't just put new tires on and do an alignment immediately on a 928.

 

Thanks to all for the responses. Particularly to the lady whose mild driving has her passengers grabbing for handholds, my mild driving puts my wife to sleep. My heavy driving puts me to sleep. I did have my '87 S4 up to 135 mph when it was new and I was only 50 years old.