Wheel bearings won't cause this problem. Shaking when moving has to be caused by a rotating part, and while a bent hub could do that, the shaking would still be there during coasting. Here it is not shaking during coasting. Also, it is nearly impossible to bend a hub unless it was in a really hard crash. The strut or the lower control arm will bend first to absorb the shock. To identify a bent hub, we would start by observing the left and right wobble of the wheel while we run the engine, in gear, on a hoist. If "lateral run out" is excessive or even noticeable, the next step would be to remove the wheel, then measure the run out on the brake rotor on the wheel's contact area, not the braking surface. If that is excessive, we would remove the rotor, then measure the run out on the hub. It is almost a certainty there would be no run out on the hub, and inspection would reveal debris stuck between two of those parts, especially if the problem first occurred right after some other service was performed that required removing the wheel. A wheel bearing will become noisy long before it becomes sloppy. If you can put up with the excessive noise for two to four years, eventually some play will develop in the bearing, but even that won't cause shaking. Unlike the bent hub or debris caught between two parts, which causes a wobble by forcing the wheel to push the tire's sidewall left and right, a sloppy wheel bearing gives the wheel the freedom to squirt out on the bottom. While rotating, none of the other rotating parts put any sideways stress on the wheel or tire.
When tires are replaced, rust and scale can break off the rotor and fall down behind it. Once the wheel is reinstalled, that scale gets caught between the hub and rotor, and that prevents the rotor from sitting squarely on the hub. The rotor will wobble, and since the wheel sits against the rotor, it will wobble too. You'll feel that when accelerating and when coasting. It is also common with cast wheels for a chunk to corrode off and stick to the rotor when that wheel is removed. If we forget to check for that and clean the rotor off, that debris will get clamped between the wheel and rotor and also cause wobble.
The most common but really elusive cause is the inner CV joint housing has worn spots. The original person said the half shafts were replaced multiple times, but this wear can easily be overlooked when core shafts are being inspected and rebuilt. This question is eleven years old. In the last three years, I bought a right half shaft for my '88 Grand Caravan, and paid less than 65 bucks for a brand new shaft, not a rebuilt one. Ten years ago a rebuilt shaft could cost over twice that much. It doesn't pay today to buy anything but a new shaft. That will guarantee you won't get one with a worn housing.
I ran into a half dozen of these worn housings in ten years working at the dealership, and figured out what to look for. There is no way to tell if the wobble is being caused by the left or the right shaft, but in my experience, only one left housing was bad. All the others were on the right side, so start with that one. You have to slide the boot back, then remove a wire ring, bend some of the tabs, or simply turn the housing at a high angle to the shaft to remove the tripod. There will be three large rollers sitting on needle bearings. Be prepared to put tape around them to hold them onto the shaft. Some can slide off from gravity. Some are held on with wire rings.
Wipe the grease out of the housing, then run your finger over the six highly-polished surfaces the rollers run back and forth on. If you can feel even the slightest hint of a depression, you have some serious junk, and it was causing a real miserable wobble during acceleration. If it feels okay, wash all six rolling surfaces, then shine a trouble light in there and look at the reflections. If you see the slightest wave or distortion, you found the cause of the wobble. This is similar to feeling the nice smooth bodywork under the doors of a show car, but you can see the waves in it when looking at the reflection of the ground in the paint. In both cases, the waviness is easier to see than it is to feel.
With each rotation of the shaft, the rollers allow the angle to change between the shaft and the inner housing. To do that, the rollers are running back and forth about a half inch. Those angles change due to the height difference between the transmission and the wheel bearing, turning the steering system, and the height changes the suspension system goes through. You can have a badly worn housing that doesn't cause any symptoms, as long as the rollers always stay within that area. The wobble will show up when something changes the area the rollers want to run in. The most common cause is replacing an engine mount. On a '90 model, the right mount positions the engine from left to right. Even if that mount is just loosened, then bolted back on in a different location, that can move the engine to one side up to about 1/4". That is way more than enough to shift the area where the rollers run in the housing, and that will cause the wobble that wasn't there before.
Changes in ride height can affect this too. Springs sag with age, but this happens so slowly, and since the suspension system is constantly bouncing up and down, the area of wear increases gradually without our noticing it. As an alignment specialist, I am very critical of correct suspension system ride height, and I want it to be right before I'll take your money for an alignment. That means replacing the coil springs. That raises ride height and changes the geometry of the suspension system parts. That moves the rollers to a new location in the housing. Now they'll roll into and out of the worn area. During cruising and coasting it is easy for the rollers to move back and forth. With the torque of acceleration, however, the rollers bind when trying to run out of the worn area. Instead of rolling smoothly, they push on the shaft. That pushes on the outer CV joint, which pushes on the wheel bearing, which is bolted to the spindle, which tugs on the lower control arm, which is mounted on rubber bushings. The spindle is being pushed left and right, and the steering linkage is attached to that and is also being pulled back an forth. The important observation hat was never made clear here is it is the steering wheel that oscillates back and forth, and this usually occurs when turning and up to about 35 mph, as in when accelerating from a parking lot onto a street. Since the binding rollers won't let the shaft change length freely, it also pushes back and forth on the transmission / engine. That is what is felt as the whole van is shaking.
When the customer says other repairs were done recently, I look at the right engine mount to see if was moved. The two mounting bolt heads are on top, with built-in washers. Those washers leave little silver dots in the black paint to show where they were. If you see those, trying repositioning that mount to where it was previously. Regardless if the shaking is gone or not, moving the mount almost always causes the symptoms to change, which is proof you're looking in the right area. You may be able to eliminate the shaking to the point it is not noticeable, but that is not the total fix. No other rotating parts will be affected by moving the engine, so you have proof the cause is an inner CV joint housing. The shaking could get worse too, but again, the inner joint is the only thing that changed.
The control arm design you don't like applies to the miserable '96 and newer models. This question refers to a '90 model which was the last year for the best design version they ever had.
Monday, October 16th, 2017 AT 6:48 PM