Is there a bowling ball in my engine?

Dear Car Talk

Dear Car Talk | Oct 01, 1989

Dear Tom and Ray:

I have a question about my 1981 Jeep CJ 8 Scrambler. When I have it in 2 wheel drive and hit a bump, it sounds as if a bowling ball is loose under my feet. When the wheels are locked into 4 wheel drive, the noise never occurs. Accelerating or shifting into neutral does nothing to change the vibration or noise. Is this vehicle safe and is it capable of pulling a two-horse, five thousand pound trailer?

TOM: This vehicle wasn't safe the day you bought it. But let's discuss your mechanical problem--there may be a solution to that. You probably have a bad U-joint on the front half of the drive train. This car has, in effect, two drivetrains. When you're in 2 wheel drive, you're using the half that powers the rear wheels. If a U-joint on the front drive shaft or front axle shafts was bad, it could bounce around in 2 wheel drive and cause the "bowling ball" effect you describe. Switching to 4 wheel drive tensions the front drivetrain and prevents the loose part from moving.

RAY: Take this car to your mechanic and ask him to check all of your U-joints. We actually recommend that you pull a two-horse trailer when you do this. That way if the driveshafts fall out along the way, you can unhook the trailer and have those two horses pull the Jeep. You'd only be losing a few horsepower.

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