Mercedes R107 450SL Belt Check, Replace, Tension Adjust

It's often very easy to ignore regular service items when owning a classic Mercedes-Benz. No reminders from the dealership, no milage reminder on the dash, etc. So it is important to be your own service advisor and make a schedule of everything you do and when it needs to be done next.

With regard to to the R107, regular inspections such as checking the belts and replacing when needed is critical. 

CHECKING THE BELTS

The Mercedes R107 450SL has 6 pulleys, one tensioner wheel, and 5 belts. 

1. Alternator (1 - 4) 2. Smog Pump (2 - 4) 3. Water Pump (3-4-7) 4. Engine Crank Pulley 5. Belt Tensioner 6. AC Compressor  (6-5-4) 7. Power Steering (7-3-4).

ALTERNATOR BELT - REMOVAL OR ADJUSTMENT

Only loosen bolt enough to allow movement

SMOG PUMP BELT - REMOVAL OR ADJUSTMENT

Only loosen bolt enough to allow movement

WATER PUMP & POWER STEERING BELT - REMOVAL OR ADJUSTMENT

Only loosen bolt enough to allow movement. NOTE: The power steering unit also provides the tension adjustment for the water pump pulley.

AC COMPRESSOR BELT - REMOVAL OR ADJUSTMENT

Only loosen bolt on tensioner enough to allow movement.

BELT INSTALLATION ORDER

When installing the belts, the following order must be used: Power steering to water pump to crank (X2), AC Compressor to tensioner to crank, Alternator to crank, Smog to crank. When one belt is beginning to show signs of wear, all belts should be changed. 

BELT TENSIONING

Belt tensioning is critical for each of the components they are driving, so don't guess.Tension that is too loose will cause the belt to slide in the pulley grove causing damage to the belt and polishing of the pulley, in addition it will cause erratic operation of the component being driven, causing potential damage or safety issues. Subsequently belts that are too tight, will likely cause damage to the driven components by damaging the component's driveshaft and or damaging the components bearings. Every manufacturer provides specific belt tension for each model they produce. 

For the 1975 Mercedes-Benz 450SL the tension for each belt is 23kg or 50lbs.  I use the Gates 91107 Krikit V-Belt Tension Gauge which is an inexpensive and quick way to do the job right.