The problem is finally found it's a bent hub. Vibration is not really a simple problem to solve because it can come from many sources. I let you know what my experience and readings had listen to me, this is a check list by priority.
- A common cause is a wheel imbalance, it can be a good start to get it check in a shop. It doesn't cost a lot.
- Do a road test, drive until the vibration occur, then get the transmission in neutral, if the vibration continue it eliminates the possibility that it comes from the motor or transmission mount.
- Check for a worn steering tie rod ends inner and outer.
- Check the control arm ball joint and the bushings.
- Other sources of vibration may come from tires, wheels, hubs. A good way to pinpoint those problems is with a dial indicator. There is a good article on this subject in the Popular Mechanics web site, the name of the article is "Diagnosing And Repairing Wheel Vibration". To summarise the goal is to measure the deviation on some points, radial and lateral, first on the tire, if the deviation exceed the limit the check is done on the wheel if the deviation is out of spec the measure is done on the hub. With this procedure it's possible to determine the origin of the offset, tire or wheel or hub, in my case it was the hub. I haven't found a dial indicator in my sector so I used the poor man dial indicator made from a hanger, and I used my calliper to measure the deflexion. The precision was sufficient on tires and rims but not an off for the hub.
- Lift the two front wheels and start the motor, then look the rotation of the wheels if the offset is important you will see it right away, it was my case, the offset was two times the maximum permitted.
- Verify the sway bar bushings and links
- Verify the shock absorbers, bad shocks may amplify the vibrations
- An alignment is not the good choice since it's normally not a cause of vibration.
Good Lock