when hitting 70mph my car starts to shake violently and dosent stop till im doing about 85mph (on my private airfield of course)

ive had the geomotry checked and all the wheels balanced twice.

any other ideas of what it could be and how to check??

Cheers
Dan

 

That does sound like the balancing is off, even though you have had them balanced. Do you have one of these puncture repair fluids in the tyres? I had to have all my wheels stripped and cleaned prior to re-balancing as this stuff does not allow the wheels to be balanced acuratlly.

spelling off because p!55£d.

 

If the unbalance is not felt through the steering, but throughout the car, I would check the parts that rotate with vehicle speed at the back of the car. Starting of with tyres, wheels, brakes, driveshafts and propshaft.

 

i have a similair issue but mine is intermittant,upto 60 mph its fine then wow,extreme steering wheel wobble and cabin vibration,sun visor hits roof etc 70 still the same down to 30 mph still doing it (on a bypass) then back to 60 still doing it 5 - 10 miles later puff,stops and car is fine for a day or so

wheels are balanced too

have just rotated the wheels so fronts are now on the rears and vice versa and it didnt do it last night,but im not holding my breathe,will give it a week before i say its cured.

maybe rotate the rears to fronts, shouldnt be the wheels as they are balanced but hey,weird stuff happens

 

Check your shock absorbers.

I had this problem, changed tyres, still shook, chenged brake discs and pads - still shook
changed shockers and had geometry reset and it had cured the problem.

Where in the country are you based?

C