Chrysler Repair: minivan front end shakes when accelerating/braking, cv joints, wheel bearing

Question
Hi, my Chrysler Caravan shakes when I accelerate over 45 mph and really shakes badly when braking at over 35 mph. I live in Costa Rica and nobody here knows these cars, the dealership included. I've tried alignment, replacing all tie rods, tires, balancing - it just gets worse. Also there's a strong humming sound when I turn the steering wheel - can't find a mechanic to fix that down here. Worried about this front end shaking - dangerous?

Answer
Hi Joe,
My first thought is that one or more of the 3 engine mounts is fatigued or broken because the torque that is demanded of the engine when either you accelerate or decelerate is expressed between the engine and the body through those rubber-based engine mounts. The rubber can crack or even break which then allows the engine to move back and forth or side to side so much as to vibrate or rub metal against metal. While a helper is in the driver seat and you at the hood opening to observe the engine, have the helper (with the parking brake 'on' and his foot on the brake pedal and with the engine idling) shift the trans into drive and then into reverse and watch to observe the motion of the engine when the shift is made. It should move only a little bit in its position. Otherwise if it shifts radically then the mounts (all three of them) should be inspected and any that are fatigued should be changed out. To exacerbate the motion the helper could rev the engine just a bit before doing the shifting.
The other possibility is that one of the cv joints (four in total, two on each half-axle) is dry and hanging-up which, however, makes a clicking sound (not a humming sound) when you accelerate/decelerate. If that were the case you would find by visual inspection that the rubber boot (ribbed rubber cylinder) is cracked and leaking grease.
So the sound is an important thing to consider. Because you say the humming occurs when turning, it might be a wheel bearing (but I would describe that as a "growl"). The "humming" makes me think it is the engine mount(s) due to the metal of one side of the mount coming in contact with that of the other side when you are turning/decelerating which due to the natural vibration of the engine running is now felt in the body and as a humming noise.
So I lean first toward the mounts as the problem.
Roland