Here's how to replace the tensioner:
Tools you will need:
Set of Torx sockets
Torque wrench (needs to be able to torque to 25ftlbs)
1. Remove the electric fan assembly.
A. disconnect electrical connector for fan located on one bottom corners, drivers side I believe(1 connector only)
B. On the top of your radiator support (cross section that has your headlights, fan and radiator mounted to it) you should see at each corner of the fan assembly mountings that hold the fan onto the support, they should be 10mm bolts. Remove them.
C. Your fan should be loose from the vehicle. Carefully pull it out paying attention to your coolant hoses and transmission cooler lines going into the radiator. This will be a tight fit (but is possible with the right force)to get out but if you are having trouble you will need to disconnect one of the transmission cooler lines to make it a little easier. (the transmission line is a steel line , like a brake line, that goes into the side of your radiator. They are usually mounted on the passanger side of the radiator. There will be one at the bottom of the radiator and one about mid way up the radiator. If you cannot get the fan assembly out remove the middle trans line off the radiator, there is a fitting at the radiator on the line that you will loosen. You will loose a little trans fluid but if you plug it it's not enough to cause any trans problems if your fluid is at th proper level.
2. Now with the fan out you will remove your belt.
3. Now get a look at the tensioner and note a hole a little smaller than a pencil on the bottom (item #6 on the diagram Drift Pin) You will need to put a a nail (2 inch nail for woodworking will work)in this hole while turning the tensioner like you are relieving pressure off the belt. This hole will line up with another hole when tension is take completely off the tensioner. Once these holes line up put your nail through them. This will hold the tenisioner in place so that you can access the tensioner mounting screws behind them. (Note your new tensioner will already have the pin installed)
4. To remove the 2 bolts holding the tensioner on you will need a set of Torx sockets. You can purchase these at most autoparts stores for a 5-10 bucks and they are extremely useful and necessary if you plan on working on your MB in the future.
5. Be easy!!! A very important note! This tensioner is mounted to an aluminum front timing cover and can strip very easy if you over tighten bolts! If this gets stripped you will be looking at a good $1000 to replace. Not to scare you but to emphasize the importance of proper torque on this repair. So when removing do not use air tools (no air ratchet) use a standard ratchet. Also make sure you have a torque wrench that can torque 25ft lbs (available at auto parts stores for around $50-100.)
6. Now remove the two mounting bolts with your torx socket and standard ratchet.
8. Once removed the tensioner will come right off.
9. When reinstallting it is a good idea to put a dab of anti sieze (available at auto parts stores) on your bolt threads. This prevents the steel bolt from pulling the aluminum threads.
10. When starting the bolts run them down as far as you can by hand making sure not to cross thread. Then torque them to 25 ft lbs (no more). Once torqued you can remove the drift pin installed on the new tensioner. Now reinstall the rest of your components in reverse order.
If you need anything further just let me know.
Saturday, January 31st, 2009 AT 1:48 PM