451 CDI AC Belt Change

Mod Description

Changing the air conditioning belt on the diesel isn't the same as the petrol model, they didn't put a pretensioner on that belt for you to loosen to enable the belt to just pull off. However, the alternative is actually easier and doesn't require you to retention the belt correctly afterwards.

Mod Details

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This is a photo of the belts taken from the underside of the car. The narrower belt runs between the air conditioning pump at the top of the engine and the smaller pulley attached to the crankshaft.There is nothing else in between such as a a pretensioning wheel. These usually sit mid way and take up the slack. The pretensioner is adjusted to bring the belt up to a selected tension. Normally, this pretensioner is loosened to make the belt loose, the belt can then be taken off easily by hand.

With the lack of pretensioner, you need another way to get the belt off.

The tool you require is smart part number 451 589 01 61. It costs about £10 and is made of aluminium. Alternatively you can buy a 3D printed copy that also comes with an alternator tensioning tool for the other belt. These are 3D printed by a fellow smart owner and currently for sale here. Easy Green tools.

Jack the car up, remove the rear right and wheel as you look at the back of the car. Remove the belt cover by removing the large plastic plugs before pulling the plastic shield from the car.

Place the tool over the pulley as shown below.

Using a Torx E18 spanner on the pulley bolt, start turning everything anti(counter)clockwise.

As you turn the pulley, the tool moves around and unseats the belt. Help it over with your hand.

Of course, there is a far quicker and easier way to remove the belt if you are replacing it. Get the equipment that your Mum uses to cut your hair. (You can leave the bowl though). Reach in and cut the belt, it can then just be pulled out from the car. 5 second job.

Here is the new belt. WOW huh! Exciting picture. The part numbers for this belt is 001 993 76 96.

Hook the belt over the air conditioning pulley, make sure it is running in the middle.

Pull it partially around the lower pulley and place the tool over the belt as shown.

Using the same Torx E18 spanner, rotate the pulley anticlockwise and it will bring the belt around and seat it in place. Remove the tool and double check that the belt is properly seated on both pulleys. Start the car and check the belt once more. The belt is now fitted and correctly tensioned.

When Should I Change This Belt?

The air conditioning belt isn’t at all important to the running of the car. If it snapped whilst you were driving, you wouldn’t notice until the air conditioning stopped working. There is no set time when you should change these, I believe smart just suggest changing them when they become worn or actually snap.

Personally, I think it makes sense to change it when you change the serpentine belt behind it as you have to remove the AC belt to get to it. The larger belt should be changed every 40,000 miles (60,000km).