serpintine belt
 

where is the tensioner for the belt on a 90 300SEL? I can't seem to find it anywhere. I want to remove the alternator.

If you just want to remove the alternator it is possible to take the lower bold of the alternator out and flip it up.
That releases all tension from the belt.

Rob

Great thanks! Is there a tensioner on there though?

The tensioner is on the other side of the engine.
There is a small shock absorber attached to the top of the engine, that shock absorber goes to the tensioner.

To adjust the tensioner you have to release the big bold that goes trough the tensioner first, then adjust with the long nut next to the steering fluid reservoir . Best to soak it first with penetrating oil.

There is a indicator on the front of the tensioner.
Set the indicator to the first mark when the tension is released, with full tension it should be at the 7th mark (if you tensioner is still OK, the rubber tensioning parts do wear out).

Rob

Great tip on loosening the alternator bolt to get belt loose! I have to do my daughter's water pump tomorrow and I didn't want to remove fan clutch and all...thanks!!!

Best of luck changing your water pump without removing the fan and fan clutch on a M103 engine.

I know how to get fan clutch off and have done it but why does it need to be done if you can get the belt off another way? Is it in the way somehow? Just curious. The manual doesn't show to remove the fan or clutch:

http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/103/20-2100.pdf

WOW!!! 5.5 Hours to replace my daughter's waterpump and YES, you have to remove the fan clutch and everything!!! The forum is always right!That was the hardest repair I've ever done myself. I needed to use every tool and angle thingy available. Removed pulleys, tensioner bracket, tensioner, etc. No wonder they want so much money to do that job at the repair shop. I think I can do it in under 3 hours next time though. All of that because of a .20 cent rubber band gasket on the bottom of the pump. I put a new pump in anyway. Total price for parts...$234.00...labor...just my aching back but a great sense of accomplishment.

5.5. hours for your first M103 water pump replacement is not too bad - others have taken 8 hours plus.

That small O ring on the waterpump is a pain:mad::mad:

i've done it twice....5.5 hours is about right....took me that long the second time too, I think

water pump replacement
 

You guys must be thoroughly versed in the european mechanics of maintenance. I have a 1992 300 ce that needs a new water pump and after a thorough search of threads and websites, I thought it would be difficult, but not as hard as I am encounerting now. Is there a simple trick to getting the clutch fan off besides trying to locate the small hole behind the pulley. I cannot for the life of me locate it. I was able to squeeze a 10 open end wrench onto one of the pulley bolts, but that did not work. I'm pretty mechanically inclined when it comes to hot rods, but this is extremely frustrating. Any help would be greatly appreciated.
Mike

My daughter's car didn't need the tool to hold the Fan Clutch pulley from behind. I could hold the belt tight and it loosened up fine. However, on my '91 300E, I had to use a metal rod with a bend in the end (I used a pegboard hanging rod and stuck it in there) and got it nice and jammed in the hole behind the pulley before I could looosen the 8mm Hex Bolt (I think) on the clutch. I also had to buy a flatter wratchet tool that would fit between the the radiator and the clutch for the hex socket. MB makes the tool for this but you can't get it locally at any auto parts store (maybe at MB dealer). Some guys use a long screwdriver and bend the end to make the tool. That hole is there on '91's and later. It was NOT on my daughter's '87! Weird! Those pulley bolts that hold the fan on are almost impossible to get off! i had to get a new fan and clutch because my fan blade was chipped. Let me know if you need anymore help. sptt144@aol.com

Steve

Do you have a 24v or M103?

M103

What you are aiming for.
http://farm4.static.flickr.com/3381/...d8d_z.jpg?zz=1
Location of pulley on engine
http://farm4.static.flickr.com/3015/...451_z.jpg?zz=1
Where to put your holding tool
http://farm4.static.flickr.com/3644/...a3f_z.jpg?zz=1
Use a 7mm allan key and use an extension such as shown
http://farm4.static.flickr.com/3642/...1430570a35.jpg