Mercedes Coupes/Sedans/Wagons 1974-1984 Repair Guide

Belts

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INSPECTION



See Figures 1 through 5

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Fig. Fig. 1: There are typically 3 types of accessory drive belts found on vehicles today



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Fig. Fig. 2: An example of a healthy drive belt



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Fig. Fig. 3: Deep cracks in this belt will cause flex, building up heat that will eventually lead to belt failure



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Fig. Fig. 4: The cover of this belt is worn, exposing the critical reinforcing cords to excessive wear



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Fig. Fig. 5: Installing too wide a belt can result in serious belt wear and/or breakage



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Fig. Fig. 6: Drive Belt Deflection (In)

Inspect the belts for signs of glazing or cracking. A glazed belt will be perfectly smooth from slippage, while a good belt will have a slight texture of fabric visible. Cracks will usually start at the inner edge of the belt and run outward. All worn or damaged drive belts should be replaced immediately. It is best to replace all drive belts at one time, as a preventive maintenance measure, during this service operation.

Under a pressure of approximately 15 lbs. (strong thumb pressure), the deflection at the middle of the longest span should be as listed in the accompanying chart.

ADJUSTMENT



Diesel Engines

See Figures 7, 8, 9 and 10

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Fig. Fig. 7: Serpentine belt routing190D models



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Fig. Fig. 8: Drive belt routingdiesel engines



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Fig. Fig. 9: To adjust the power steering pump drive belt tension, loosen the nut on the mounting stud ...



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Fig. Fig. 10: ... then tighten or loosen the adjusting screw until the proper belt tension is reached

Unlike other diesel engines, the 190D uses only one extra-wide V-belt which drives all necessary devices. An automatic tensioner eliminates the need for any routine adjustment.

ALTERNATOR/WATER PUMP
  1. Loosen the pivot bolt and adjusting bolt.
  2.  
  3. Adjust the belt by turning the adjusting bolt along the toothed rack.
  4.  
  5. Tighten the nut on the adjusting bolt and the nut on the pivot bolt. Check the belt tension.
  6.  

A/C COMPRESSOR

The air conditioning compressor belt is adjusted with a tensioning roller. Loosen the mounting nut and swivel the roller. Tighten the attaching bolt and check the belt tension.

POWER STEERING PUMP1974-76 MODELS
  1. Loosen the bolts at the front and rear of the pump.
  2.  
  3. Pry the pump outward to tighten the belt. Do not pry on the pump housing.
  4.  
  5. Tighten the screws and check the belt tension.
  6.  

POWER STEERING PUMP1977-84 MODELS
  1. Loosen the nut on the mounting stud and the nuts on the adjusting bolts.
  2.  
  3. Tighten the belt tension using the adjusting screw. Check the tension and tighten the pivot and mounting bolts.
  4.  

V8 Engines

WATER PUMP/POWER STEERING PUMP

See Figures 11 and 12

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Fig. Fig. 11: Drive belt routing1974 V8 engines



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Fig. Fig. 12: Drive belt routing1975-84 V8 engines

  1. Loosen the 3 attaching screws.
  2.  
  3. Loosen the pivot bolt slightly.
  4.  
  5. Adjust the belt tension by pushing the power steering pump outwards. Starting in 1975, adjust the belt by turning the hex headed toothed lockwasher.
  6.  
  7. Tighten the pivot and attaching bolts. Check the belt tension. If the belt is still in good shape but cannot be adjusted, the attaching bolt (2) can be removed and reinstalled in another hole. If you do this, be sure you replace the bolt in the original hole when you replace the belt.
  8.  

ALTERNATOR

There are 2 types of adjustments on the alternator. Early types use a threaded rod and later models use a hex-headed, toothed washer.

  1. On early models, loosen the 2 pivot bolts and the lockwasher. Turn the adjusting nut on the threaded rod to adjust the belt tension. Check the tension and tighten the locknut and pivot bolts.
  2.  
  3. On later models, loosen the pivot and attaching bolts. Adjust the tension by turning the hex-headed, toothed washer. Check the belt tension and tighten the mounting and adjusting bolts.
  4.  

A/C COMPRESSOR

The air conditioning compressor belt is adjusted by means of a tensioning roller (idler pulley). Loosen the idler pulley mounting bolt and swivel the roller to adjust the belt tension. Tighten the mounting nut and check the belt tension.

AIR PUMP
  1. Loosen the top mounting bolt at the front and rear of the air pump.
  2.  
  3. Slightly loosen the pivot bolt at the bottom of the air pump. Push the pump outwards by hand, until the belt tension is correct. Do not pry on the pump housing.
  4.  
  5. Tighten the mounting and pivot bolts.
  6.  

230 Models See Figure 13

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Fig. Fig. 13: Drive belt routing230 models

ALTERNATOR
  1. Loosen the attaching bolt at the bottom of the alternator. Loosen the adjusting bolt at the top.
  2.  
  3. Adjust the belt tension by turning the hex-headed, toothed washer.
  4.  
  5. Tighten the adjusting bolt and pivot bolt. Check the belt tension.
  6.  

A/C COMPRESSOR
  1. Loosen the attaching screw behind the idler pulley.
  2.  
  3. Swivel the idler pulley to adjust the belt and tighten the mounting bolt.
  4.  
  5. Recheck the belt tension.
  6.  

POWER STEERING PUMP1974 MODELS
  1. Loosen the 2 mounting bolts and lever the pump outwards to tighten the belt. Do not pry on the pump housing.
  2.  
  3. Tighten the attaching bolts and check the belt tension.
  4.  

POWER STEERING PUMP1975-76 MODELS

On 1975 models, you'll have to swing the evaporative canister aside and remove the battery and tray to allow access.

  1. Loosen the mounting bolts at the top and bottom.
  2.  
  3. Locate the adjusting nut at the rear of the power steering pump carrier. Loosen the locknut on the adjusting bolt.
  4.  
  5. Turn the adjusting bolt to adjust the belt tension and tighten the locknut and mounting nuts.
  6.  
  7. Check the belt tension and be sure there is sufficient clearance for the power steering pump supply line.
  8.  

POWER STEERING PUMP1977-78 MODELS
  1. Loosen the mounting nut and bolt on the face of the pump.
  2.  
  3. To adjust the belt, loosen the hex-headed, toothed adjusting nut and bolt and turn the bolt.
  4.  
  5. Tighten the adjusting bolt/nut and the mounting nut and bolt. Check the belt tension.
  6.  

VACUUM PUMP
  1. Loosen the attaching bolts at the top and bottom.
  2.  
  3. Adjust the belt by swivelling the vacuum pump outward.
  4.  
  5. Tighten the attaching screws and check the belt tension.
  6.  

AIR PUMP1975-76 MODELS
  1. To allow access to the air pump adjustment on 1975 models, pull the evaporative canister aside and remove the battery and tray.
  2.  
  3. Loosen the mounting nuts and adjust the belt tension with the threaded adjusting rod. Tighten the attaching screws and check the belt tension.
  4.  
  5. Replace the battery, battery tray and evaporative canister.
  6.  

AIR PUMP1977-78 MODELS
  1. Loosen the mounting bolts and the nut on the rear of the hex-headed adjusting bolt.
  2.  
  3. To adjust the belt tension, turn the hex-headed, toothed lockwasher.
  4.  
  5. Check the belt tension and tighten the mounting nuts and nut on the rear of the adjusting bolt.
  6.  

6-Cylinder Engine See Figure 14

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Fig. Fig. 14: Drive belt routing6-cyl. engines. On 1974-76 models, the air pump is below the power steering pump

ALTERNATOR
  1. Loosen the upper (adjusting) bolt and the lower (pivot) bolts.
  2.  
  3. Models through 1976, and 1977 and later air conditioned models can be adjusted at either end of the upper bolt. One end is a hex-headed, toothed washer and the other end is 6 mm square. All other models are adjusted with the hex-headed toothed washer.
  4.  
  5. Tighten the upper and lower nuts/bolts and check the belt tension.
  6.  

POWER STEERING PUMP1974-76 MODELS

Loosen the adjusting (lower) bolt and pry the power steering pump outward to tighten the belt. Tighten the adjusting bolt and check the belt tension.

POWER STEERING PUMP1977-81 MODELS
  1. Loosen the attaching (pivot) bolt on the face of the pump.
  2.  
  3. Loosen the nut behind the toothed adjusting bolt.
  4.  
  5. Turn the hex-headed toothed lockwasher to adjust the belt.
  6.  
  7. Tighten the nut and pivot bolt and check the belt tension.
  8.  

A/C COMPRESSOR

The air conditioning compressor is adjusted at the idler pulley. Loosen the center screw of the idler pulley and adjust the belt tension with the adjusting screw. Tighten the center screw to 12 ft. lbs.

AIR PUMP

Loosen the adjusting bolt and adjust the belt tension by prying the air pump outward. Do not pry on the air pump housing. Tighten the adjusting bolt and check the belt tension.

6.9 Models See Figure 15

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Fig. Fig. 15: Drive belt routing6.9 models

POWER STEERING PUMP
  1. Loosen the attaching bolts and nuts.
  2.  
  3. Loosen the nut behind the toothed adjuster.
  4.  
  5. Adjust the belt tension by turning the hex-headed, toothed washer. Tighten the adjusting nut and mounting bolts.
  6.  
  7. Check the belt tension.
  8.  

AIR PUMP

Loosen the attaching bolt and adjust the belt tension with the adjusting screw. Tighten the attaching bolt and check the belt tension.

A/C COMPRESSOR

Loosen the pivot bolt and the bolt in front of the toothed adjuster. Turn the hex-headed toothed adjuster to adjust belt tension. Tighten the adjusting bolt and attaching bolt. Check the belt tension.

ALTERNATOR

Loosen the upper and lower nuts on the adjusting and pivot bolts. Tighten the belt by turning the toothed washer and retighten the nuts. Check the belt tension.

 
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