Belt tensioner shock: Do I have one or not?
 

Hello all,

I know this sounds like a dumb question but I have seen conflicting info on this so I want to check for sure.

I have a '97 S320 (M104) that has developed a rattle that I have traced to the front part of the engine bay. It only rattles in gear when the car is at operating temp. Everything I have read says that this is most likely the belt tensioner/shock.

I have looked around a good bit to try and find it but I can't seem to locate the shock because there's not a whole lot of room up front to get a real good look. So...

1. Should this car have the old-style (with shock) or new-style (no shock) tensioner.

2. If it has the new-style tensioner, is the above diagnosis still valid for do I need to start looking at other things?


Thanks!

this site http://www.detali.ru/cat/oem_mb.asp has diagrams of all the MB models.

Could the tensioner be all that buried? I can't imagine changing an accessory belt requiring lots of labor time.

I checked under cooling system in the `Buy Parts` tab at the top of this Mercedesshop ) page and under cooling system it shows the tensioner shock $45.

I'll lead you wrong a second time - when my tensioner went bad it sounded more like a squeak then a rattle

To be led down the merry path a 3rd time, try this: Drop the belt and run the engine for 30 seconds. If sound is gone, its possibly the tensioner or accessory (alt, ac, etc.) related. Second test is reconnect the belt and using a rubber bushing on your floor jack, raise the engine 1/4" at teh oil pan (no more or YOU will cause damage). If sound is gone its likely a motor mount casuing excessive engine vibration showing up at the belt.

I have found the electronic parts catalog to be very helpful in determining what parts are on my car. The Mercedes on line EPC subscribtion is free but you have to give them your credit card info anyway. You put in your vin and if you click on a part that is not on your model it will tell you that that part is not used.
https://epc.startekinfo.com/epc/subscribe.jsp

I'm pretty sure that the 97s do not have the shock but have the automatic tensioner instead of the manual adjuster with the shock. Quick check is to look between the water pump and power steering pump for the adjuster. There will be a hollow 1/2" round protrusion sticking straight up (~2") with a 13mm hex on the top portion of it, in a goldish anodized color. If you see the adjuster you should have a shock too. No adjuster = automatic tensioner and no shock.