'89 911 steering vibration problem

[crbox]

Have recently aquired a very good 89 Carrera 911 with a problem that's spoiling the ownership experience. Steering wheel vibrates between 80 & 95 mph. You can feel it through the foor also. Naturally you would think front wheel balance. I've had it done by two separate outfits and both showed negligible issues - just 5g out. I carefully checked the wheels the 2nd time for out of roundness and they are near perfect and there's no apparrent damage whatsoever. When the wheel was replaced I ensured that the locking nut was on the red painted stud and there was no apparent bearing play.
I've yet to examine the rack for mounting tightness, but as it's play free, runs straight and corners sublimely I can't imagine it's that. I havn't checked the rear wheel balancing or had a laser alignment done - but can't help but feel as it tracks true - they'll be okay.
Cars sits on 6 & 8" Fuchs and set at 29 & 36 psi. Compared to my prev 87 car, I would only say than the steering wheel doesn't writh about at slow speed quite as much as I remember.
Any ideas?

[c2look]

At those sort of speeds, a likely cause is out of balance rear wheels. Obviously, it could be something else but this is certainly the route I would choose to investigate first. Also, you can have the wheels balanced while they are still on the car, if the off the car method doesn't yield an improvment, though not every tyre depot may have this equipment. Certainly the cheepest option for starters