Mechanics

81 THUMPING NOISE

1981 Mercedes Benz 240d • 4 cylinder 2WD Automatic • 145 miles

1981 Mercedes Benz 240d 145k miles, runs well except for thumping noise coming from back end. Noise sounds like a flat tire but isn't. Thumps at lower speeds then dissapates, then reappears at higher speeds then also when decelerating. So not sure if this is common prob with wheel alignment, or something worse with transmission. Ive been told these cars dont have CV joints, but it sounds similar to that prob with other car I owned. Obviously my mechanical knowledge if very limited. Will have it diagnosed soon by mechanic, but any advice or info would be greatly appreciated. Thanks.
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MrJasonVoorhees
December 17, 2010.




You want to get under the car and grab onto parts like the shocks and your rear sway bar links, as well as the two axles to see if anything is loose. These are common places for noise. You don't have to pull the sway bar links very hard, as they are pretty small. They are just inside of your wheels and attach to the sway bar, a picture attached. They are also cheap ($20 for two), and if you have a wrench, Alfred E. Neuman could make the repair.

A 240 or 300 has 2 CV joints, covered by rubber boots, on each axle. If you look at the bottom of the car, you will see the two axles coming out of each side of the differential. There is an inner and outer joint, as this is an independent suspension. If a CV joint can cause this kind of noise, maybe that is your problem, especially if the rubber boots are worn, and there is no lubrication. Look to see if the boots are split open anywhere. The differential, for the most part is fixed. You should check to see if your differential mount is shot.

There isn't a lot to go bad on the rear suspension, although it can be about as expensive to totally redo as the front. Rear body mounts can cause alignment problems, the bearings in the side of the differential can be noisy, the shocks can be loose, and clunk and cause other parts to clunk, the sway bar links tend to clunk when you stop and start in either direction, and the rear trailing arm bushings can go bad, also. I don't think they make noise unless they are really shot. To replace the whole front end, the parts are about $7-900+, including springs, plus a $1000 for labor or more. Other than the differential and its bearings, the cost is about the same. The parts are very large, so you normally are replacing shocks, springs, bushings, sway bar links, and the axles. The axles cost about $130 each.


Tiny
Rbmay
May 20, 2011.
TIRES SHOT?
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Tiny
Rbmay
May 20, 2011.
REAR AXLE AND DIFFERENTIAL MOUNT and PHOTO OF TIRE THAT MAY CAUSE SOME THUMPING


Tiny
Rbmay
May 20, 2011.

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