Belt looks worn and starting to squall, I've changed belts in other brands of cars and trucks. Anything special about a 93 300D 2.5L that I have to watch out for? Special tools?

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1993 MB 300D 245K died.

It's easy as pie

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

You can change the serpentine belt with only the 13 mm wrench and the lug wrench from an original tool kit.

First order of business is make sure you understand the routing of the belt, it will go on the wrong way with almost enough slack or with a bit too much slack, find or create a diagram before you pull the old one off.

Loosen the 13 mm nut holding its bolt in place securing the tensioner spring cam block, use the handle of the lug wrench in the hole in the top side of the cam block, leverage the wrench enough to relieve the tension on the cam block and allowing the bolt to be slide backwards towards the rear of the engine, with that long bolt mover rearward enough so that its front end clears the black plastic cam block, that allows the cam block to pivot further along its range of motion relieving the tension on the serpentine belt, the serpentine belt can then be maneuvered of the pulleys.


At this point you're ready to dig in deeper, I uncouple the hose that goes from the head to the coolant reservoir so I can swing it out of the way, disconnect and swing out of the way any vacuum lines that might be in the way. I take off the under engine sound encapsulation panel.

It's easier to change a belt with the fan and clutch off the water pump but it can be done with them in place. Your car should have a two piece fan shroud, separate the inner extension ring from the shroud, then take the clips that hold the shroud to the radiator off, you can then slide the shroud itself upwards out of the space between the fan and the radiator. Then you can pull the inner extension ring forward off from around the fan and clutch.

If the fan is in place you get the belt off a couple pulleys and then you work it over and around the fan turning the fan so as to bring the belt in between the blades out and around them.

I get the new belt in and around the fan first then make a loop that I can pull in between the crank pulley and the tensioner, that loop wraps around the idler pulley on the tensioner , the back side (unribbed "outside") rides around that idler pulley. Then I get the pulley strung under the crank pulley up around the AC compressor, you can then kind of hold it there with one hand (holding slight tension so it stays lined up in the lower pulleys and then get the belt around the alternator pulley, and then the water pump pulley. Pull up on the belt pulls the slack out and positions the belt to get over its edge and onto the PS pump pulley. If the fan and clutch are off it is easier to get the belt onto the water pump pulley last (you can't get your fingers in close enough to get the belt on the water pump because the fan blades are too close to it.

Because I have the under engine panel off I can look and check that the belt is correctly positioned on the crank and AC compressor pulleys and the alternator as well, with the bely running correctly on all the pulleys, place the lug wrench handle back into the cam block hole and lever it to apply tension to the point where the long bolt can be slide forwards through the lined up hole in the cam block, that tensions the serpentine belt, reinstall the 13 mm nut securely, place the inner extension shroud down and around the fan, slid the shroud into place making sure it's lined up to avoid the fan hitting it , make sure the two plastic tabs of the shroud bottom edge are in the correct position in the slots they fit (this is another point at which having the under engine panel off makes it easier because you can look and even feel the tabs into place from below much easier than from above, also when you have to key the four tabs on the inner shroud all at the same time so you can rotate it securing it) , clip the shroud into place, place the inner shroud into position and rotate it to lock its tabs into the keyhole receptacles of the shroud, use the square peg that also serves as the hose mount to lock the inner ring to the shroud. Reconnect vac and coolant hose and throw the old belt in the truck as an emergency spare. Reinstall the under engine panel.

If you fool with the fan you need a serpentine pulley holder tool , tan 8$ version was once available through Harbor Freight (I've seen them displayed as discontinued when I bought the last one I got and you need some sort of very short stubby 8 mm Allen Head wrench tool for the fan clutch's center Allen Head Bolt. I have never regretted buying the MB specific 3/8" drive super short Allen Head socket made by Stahlwille Tools, less than $20 saves $100s in aggravation. To remove the fan after get the shroud loose/out you use the pulley holder tool from the back side of the water pump pulley to cam and therefore counter hold the pulley as you use the stubby 8 mm tool to break the fan clutch cent bolt free. That bolt is pretty good sized, torqued pretty good and coated with blue thread lock so it can be a bear sometimes especially if it hasn't been remover before.

make sure the tensioner pulley is not worn before replacing.

inspect it by noting that the belt is close to center on the flat running surface.

When you get the belt off, make sure the tensioner bearing is good. The tensioner should move freely up and down, but you shouldn't be able to move it front to back. If you can, replace it.

And replace it without cracking the front engine cover!

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1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42