Mechanics

VIBRATION DURING ACCELERATION

2001 Cadillac DTS

Suspension problem
2001 Cadillac DTS V8 Front Wheel Drive Automatic 125000 miles

My 2001 DTS has a rough steering wheel shake while accelerating rapidly. But vibration seems to subside or disappear altogether when backing off on the accelerator. Still get some small vibration while driving at normal speeds at times. I have had the hubs and inside of the rims cleaned and new tires put on it recently. Some vibration is gone but the shaking of the wheel during hard acceleration is annoying. Sometimes the " Service Suspension System" message comes on but resets easy with dashboard reset button. I just had a " new" engine installed at 124000 miles with 36000miles on it. Also, there is a noise that sounds like its coming from the right front wheel that gets louder when accelerating and goes away when stopped. Sounds like a pulsating hum - almost like 4x4 tires on the freeway.
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Ccaruana
April 20, 2010.



Hi ccaruana. Welcome to the forum. Sounds like two different problems. Did these start right after the engine was replaced? The shaking is typical of worn spots on the roller surfaces inside the inner cv joint housing, usually the right one. The slightest amount of wear will cause the rollers to bind when the shaft changes length and angle. The extra torque of accelerating increases their resistance to moving freely. When the shaft can't change length as it rotates, it pushes on the that spindle which tugs on the steering linkage. As you reduce torque on the drivetrain, the rollers can move freely and the binding stops. This problem can show up after doing engine or transmission work because it is likely they won't be in exactly the same position as before so the rollers travel in and out of the worn spots that developed earlier.

If the hum you're hearing sounds like an airplane engine, suspect a front wheel bearing. They can start this anytime from normal wear, but it is real common for damage to be caused that makes them noisy. When the engine was replaced, it was necessary to remove the two half shafts. Part of that assembly are the outer cv joints that hold the wheel bearings together. Once the half shafts' axle nuts are loosened, it is critical that the vehicle's weight is not placed on the wheels. Some people loosen the axle nuts while the tires are still on the ground. That keeps the axle from spinning so the nut can be turned, but as soon as that nut is loosened, the wheel bearing has been damaged. This happened to a car in the body shop at the dealership where I worked. The engine and transmission were removed to repair the damage. When they found out it would be a week for the parts to arrive, they put the tires and wheels on and pushed it outside. There was no drivetrain weight on those bearings, but they were both noisy during the test drive after completing the alignment.

The torque value is very important for those nuts too and is very high, typically 180 to 240 foot pounds. Again, to hold the axle from turning, some people will torque the nuts after the tires are on the ground. It's too late. Once the weight of the car has been on the bearings while the nuts were loose, the damage has been done. The only fix is to replace the wheel bearing assembly.

Caradiodoc

Caradiodoc
Apr 21, 2010.