How to replace Mercedes-Benz Tensioner
Step-by-step directions on how to replace Mercedes-Benz serpentine belt tensioner. Replacing the belt tensioner on Mercedes-Benz engine is relatively easy. It requires a few basic tools and approximately 30 minutes. This guide applies to the majority of Mercedes-Benz cars. The procedure is the same for many engines including M112, M113, M273.
The average price to change the belt tensioner at the dealer ranges between $400-$650. Local repair shops will charge between $280-$450. The DIY cost to change Mercedes-Benz drive belt tensioner ranges between $50-$120, even if you have to buy the tools needed for this job and a new serpentine belt.
What you will need
While it is not required to replace the drive belt, it makes sense to replace it at the same time as the tensioner. It is ok to use the old belt if it does not show wear, cracking, degradation or drying out.
- Park your Mercedes-Benz, set the parking brakes and allow the engine to cool down.
- Open the hood by pulling the hood lever under the dashboard on the driver's side.
- Use a 17mm socket to move the tensioner up (service) position.
- Insert a metal pin in the tensioner hole to keep the tensioner up.A 5mm Allen wrench or bolt can be used as a pin. The pin needs to be strong enough to withhold shear force. Do not use any item made of plastic as a pin.
- Slide the drive v poly belt away from the tensioner.
- Remove the top torx bolt using an E12 Trox socket and a 2" extension.
- Remove the lower torx bolt.
- Some models also have a shock attached to the tensioner. Remove the upper bolt from the shock to disconnect it from the engine block.
- Install the new timing belt tensioner. Start threading the tensioner bolts by hand until a few threads have gone in.
- Torque the tensioner bolts to the recommended manufacturer specifications. Typical torque for the tensioner bolts ranges between 25Nm to 35 Nm. Check with your dealer.
- Install the drive belt. Make sure it is routed on all the pulleys properly. If the belt does not reach, make sure it is not sitting on top of one of the pulleys.
- Put pressure on the tensioner 17mm head to move the tensioner up and remove the locking pin.
- Start the engine and ensure the belt and tensioner are working properly.
Over time the tensioner pulley can start to crack. If not replaced on time, it can fail while the engine is running. Drive belt will come off the various pulleys possibly causing damage. The tensioner pulley bearing may also fail. When this happens you would normally hear noise coming from the front of the engine.
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