Severe vibration at speed

[Tailsme]

Hi All, I have a very strange situation, I have noticed a vibration through the steering wheel and seat while driving, it starts around 65MPH and I cannot drive through it, it gets worse and is pretty severe as though the car is bouncing along the road. I have checked all wheels and have no bent rims, all tires appear in good condition and have been balanced, no bulging or uneven wear on the tires. I have checked all suspension joints, ball joints and all look to be in good condition. The car has had new shocks and springs with less than 1,000 since replacement. I checked engine mounts and again all look good. I am at a loss at what to try next.
There are no noises, no clunks, rattles or any vibration when braking.
Any help on what to try next would be appreciated.
Thank you
Darren

[3.8etypephil]

Check the condition of the catalytic converters; when they become blocked the engine starts to choke on its own exhaust as the revs rise. I was utterly convinced that I had a failing propshaft on my XJR, until I fell upon the solution quite by chance. New £70 aftermarket cats welded in, all vibrations gone, and the original performance which had fallen off so gradually that I hadn't noticed (until the day when it wouldn't exceed 110 mph in any gear), fully restored.

This is what I found when I took mine apart:

[mike020150]

Moving the gear lever briefly into neutral and letting the engine revs drop whilst travelling at 70 mph would eliminate engine/exhaust issues if the vibration were to continue. You don't specifically mention the prop shaft or drive shaft joints. The smallest amount of free play in any of them can cause major vibrations, similarly for excessive free play in the diff nose and output shaft bearings. All should be checked carefully in the search for the guilty culprit. Since the vibration is very noticeable through the steering and we have some pretty horrible roads, internal damage to a tyre can't be ruled out. Have you tried replacing each one in turn with the spare to see if the vibration disappears? Mike.

[Tailsme]

Thanks for everyone's comments, I did check the prop shaft and all joints and could not find anything wrong. I was convinced it was the tires but did not want to just put new tires when I still had plenty of tread and could not find any tire issues.
I ended up taking to the dealer for them to take a look, they had the car 2 days and could also not find anything wrong on suspension, drive shaft or any other mechanical problem.
They determined the tires were old and although the tread was good they had dry rot from the inside, and recommended replacing them. I am having all 4 tires replaced and will be picking the car up tomorrow, hopefully this will resolve the problem.
Thanks again everyone

[B87UL]

I am not familiar with your car model, but I have known similar events on up market cars, at very high speeds.

On the cars I have known, the problem has been caused by the rotation sensors / magnets/ slotted discs that govern the anti-lock brake system. These system sensors are often used for other systems such as traction control. The trouble arises when the system “thinks” there are wheel speed differences and although minor it attempts to correct the speed of a wheel.

Usually all that is required is to remove corrosion from the sensor faces, ensure the sensing components are positioned correctly and checking sensor connections for water / corrosion.

Probably worth a try to check these out.