Due to wear of the internal drive gear, the speedometer can stop working.
Car problem reports
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Most reported 1991 Mercedes-Benz 300E problems
Due to wear, high usage vehicles can experience ignition lock and tumbler failures. The ignition lock cylinder will generally require replacement to correct this concern.
Due to age and sun exposure, the interior wood trim cracks and the finish gets a cloudy haze. Replacement if the trim would be the most common solution to the problem.
A rough running motor or lack of power can be caused by a failed distributor cap or rotor, ignition wires (or their resistors), or valve cover gasket leaks. If the valve cover gasket leaks, oil can pool where the ignition wire resistor connects to the spark plug. The resistor can fail and the spark plug may not fire because of a short circuit through the oil.
One or more blend door vacuum actuators may fail resulting in the incorrect output temperature from the HVAC system. Failed actuators will require replacement to restore proper HVAC operation.
A coolant leak may develop from the water pump. When replacing the water pump, the drive belt tensioner should be inspected and most likely replaced as well.
The sunroof may not work correctly due to failed components as a result of age and wear. Repairing a sunroof can be labor intensive and very costly.
The bushings for the shifter lever wear out to the point where they break and fall out. This causes excessive movement (loose feel) in the shifter lever and a clanging-type noise when changing gears.
The electronic throttle assembly may suffer an electrical failure. It is often cheaper to send the valve to a service center for repair that to purchase a new part.
The engine wiring can degrade because the insulating material falls off leaving the bare wire exposed. This can cause many problems depending on which wires are exposed and what they touch.
Motor mounts commonly fail, causing engine vibrations to be transferred to the body. Failed motor mounts should be replaced in order to prevent damage to the transmission mount.
High mileage vehicles may develop a transmission fluid leak from one or more of the oil seals.