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Accessory Belt replacement

on the 1983 300D Turbo (OM617)

by BoostnBenz


The following VFAQ was created to help people replace their old, worn, or damaged belts. As always remember the lovely legal disclaimer that I do not accept any liability for yours or anyone’s actions who may follow any of my guides.

Maybe you don't know how old your belts are, or they are starting to show some cracking or abnormal wear, well it is a great idea to change them before it leaves you stranded. Mine didn't match and I didn't know how old they were so I went ahead and bought what I believe to be the best belt, Continental. While a person could live without a/c and power steering, there are two smaller belts which power the alternator and water pump which are critical!

Since the power steering belt is in front of all of the other belts let's start with that one first. I ended up loosening the tensioner and all three bolts. I had them nearly out to get it to cooperate, hopefully loosening all three (13mm) of them will be sufficient for you. It slides down and inward which allows that belt to come right off, this one was by far the easiest belt for me. No tricks required to put back together.

Next is the a/c compressor belt, this one was my most difficult belt to change. The problem I had was that it didn't seem to move enough to allow the other one to just slide off so I ended up undoing all three bolts which later became a problem with realigning them. This compressor also has a tensioner adjustable from the top, you just need a 10mm deep socket. It is a good idea to loosen all three bolts again, here they are out in the open so no big deal. It seems like they used 19mm sockets. In the end I ended up getting the belt on the pulley most of the way then turning the motor over, it seemed to work well.

Now that we have those two belts out of the way time for the alternator, only thing to be careful of here is to not break the tensioner bolt, as like all the other tensioners when you turn it clockwise it tightens the belt, counterclockwise loosens it. Mine was stuck and I ended up having to buy a new special bolt (~$15) for the tensioner. Remember to loosen all bolts(17mm) before changing tension. If you do not then you will either break the tensioner bolt or worse, the ears off of the alternator. Those belts came off very easily, the new ones were no sweat either. The only tip here for reassembley is that the tensioner should be turned a half turn after all the rest of the bolts are tightened. This small bind keeps everything in place. After these two rearmost belts are on you can go ahead and install the other two. I took the air cleaner out for more room, better pictures, but mainly because I was working on the front suspension at the same time. It is quite possible to do it without removing the cleaner but for the little effort required you may just as well remove it. If you're a real preventative maintenance nut perhaps now would be a good time to swap in a new voltage regulator pricing in at a whooping $13 for a generic one or mid $40s for the Bosch part. If the wear on your current brushes are uneven you may want to consider having the armature of the alternator turned.

After the alternator belts are on then put on the A/C belt and power steering belt. Tension to feel or use the Mercedes fancy gauge to determine the firmness. Remember to recheck them with your next oil change to make sure they haven't stretched too much.

2 Conti alternator belts
1 Conti A/C compressor belt
1 Conti Power Steering belt
1 Voltage Regulator (optional)

6" Extension
10mm socket with either long extension or screwdriver type handle
13mm, 17mm, 19mm sockets
13mm, 17mm, 19mm wrenchs
Flat head or phillips screwdriver for regulator (mine is flat, but I've seen phillips before)

Discuss this DIY here.


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