Since it didn't start right after the transmission replacement, start by looking for a broken belt in one of the front tires. Holler if you want to try to do this yourself, otherwise a tire and alignment shop can help. As an alternative, rotate them from front to back, then drive it. If you feel the shaking in the seat now, one or both tires on the rear have a broken belt. This is REAL common with General and Uniroyal tires, and is fairly common with Goodyear tires that are worn out.
Broken belts won't stop shaking when you let off the accelerator, but it's an easy place to start. The cv joints can cause this in a number of ways. The engine mounts should be checked to see if the rubber is cracked or deteriorated allowing the engine to hang low on one side. This will change the angles formed by the two half-shafts and could cause one of the spring-loaded inner joints to bottom out in the housing. That would cause that half-shaft to push on the spindle which would move the lower control arm which is mounted with flexible rubber bushings. Basically, the bottom of the tire is moving in and out a little, but the steering linkage is not moving with it, so it tends to tug back and forth on the steering wheel. This can happen at any speed and will often subside when you let off the gas.
Another possibility is an offset drivetrain. The passenger-side engine mount has two bolts on top that can be loosened to allow that mount to be pried left and right to center the engine. The front mount and the driver's-side mounts just slide along. Also, you can look at the front center mount to see if the rubber mount is centered in the bracket that's attached to the body under the radiator. If it's off to one side, the engine may have been shifted. I suspect this is not the problem because first of all, the center and right mounts don't have to be touched to remove the transmission, and second, if they were disturbed, the problem would have shown up right after the transmission work.
A much more common problem is worn inner cv joint housings. I'm sorry to say that your description doesn't exactly match the symptom they cause, but it's worth mentioning anyway. There are six rolling surfaces in each inner housing that rollers run on. They allow the shaft to change angles and length as the suspension goes up and down. These surfaces must be absolutely perfectly smooth or binding will occur under load. Grooves worn in these surfaces cause the rollers to bind, then the shaft pushes against the spindle and lower control arm, and you feel this as a wobble in the steering wheel. Everything seems to go in streaks. When I was at the dealership in the 1990s, I replaced about two dozen housings in a two-year period. All different years, big variety of mileage, but nine out of ten had a bad passenger-side housing. Don't know why, but the left side gave much less trouble. It was only the minivans that this happened to.
The symptom is a severe steering wheel wobble under light to moderate acceleration, up to around 35 mph. Once you let off the gas, the wobble was gone. The repair involves disassembling and inspecting the housing. If you can feel the slightest wave or bumps, you REALLY have junk! If all six surfaces feel ok, wash out the grease, then look at the reflections while shining a light on them, similar to looking at the ground reflecting in the car's body at a car show. Any slight wave in the reflection is cause to replace the housing. Complete rebuilt half-shafts now cost less than a new housing from the dealership, but you run the risk of getting one with a housing just as bad as yours.
One more thing to not overlook is a locking brake. This is usually accompanied by a hard pull to one side. Front brake calipers used to give a lot of problems years ago but it's less common now. What is becoming more common now is rust buildup inside the metal bracket holding the center of the front brake hose. The rust pinches off the hose trapping pressurized fluid and it keeps the brake partially applied. Simply opening up the bracket with a channel-lock pliers so it doesn't squeeze the hose so tightly solves the problem. However, by the time that much rust builds up, the outer casing of the hose is often cracked and frayed meaning it's past time to replace the whole hose.
It's also a good idea to have the steering and suspension components checked. Worn tie rod ends and ball joints are safety hazards waiting to happen and can cause some strange symptoms. Other possibilities include a bent wheel, snow and ice, or mud impacted behind a wheel or ice inside the tire, although the wobble wouldn't go away; and the front end severely out of alignment.
Sunday, March 22nd, 2009 AT 10:45 PM