How to replace/ adjust the serpentine belt (or fan belt)

Hi Max, just to clarify, the W123 chassis does not come equipped with a serpentine belt (a single long belt that winds between all the various pulleys on engine driven accessories). Instead is uses the older style "v-belts" where each pulley has its own belt (with the exception of the water pump and alternator which share a belt or two belts depending on the year). Anyway now that we have cleared up the terminology here is the info you need (copied from a previous answer to the same question):

Hello, in regards to changing belts on the W123 chassis, there are a few differences between model years. For example, the early model years (1977 and 1978) use a different A/C compressor and the method for replacing that belt is different than on the later models. So it would be helpful to know which year you have.

However, in the meantime here are some links that may be helpful. They are PDF files from the online factory service manual. The first is for the early style belt setup with the older compressor, the second is for the newer style. If you read the documents they help you identify which you have.

http://www.startekinfo.com/StarTek/outsi...

http://www.startekinfo.com/StarTek/outsi...

I will probably do a guide on this with full picture instructions next time I do something like replacing my water pump on one of my W123's. Look for that.