Serpentine Belt and tensioner question - Mercedes-Benz Forum
 
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post #1 of 8 (permalink) Old 03-16-2019, 07:18 PM Thread Starter
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Serpentine Belt and tensioner question

Hello everyone early apologizes if this topic has been beaten to death already and I'm just poking it with a sick at this point.

Anyway, a friend of mine noticed my belt is starting to spider, so I took it to my mechanic and he said I need a new tensioner cause it's starting to go. Is there any special Mercedes tool needed to replace this unit? I'm just going to get a kit and learn how to service it my self. But my friend said it needs some kind of torture wrench If i remember correctly? And didn't know if it's a special item I have to order.

I have the 3.5L v6 Gas engine from the ML350 in my w251 4matic
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post #2 of 8 (permalink) Old 03-17-2019, 09:00 AM
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Changing belts and the idler pulleys is relatively easy. Just take plenty of photos BEFORE you remove the belt so you get the routing correct when you put the belt back on. I haven't done a tensioner but it should be a simple bolts out, remove, fit new, re-tighten old bolts job. Use an 18 or 24 inch breaker bar and a 17mm socket to pull the tensioner pulley back, slip off the belt.

You'll need a set of TORX sockets, metric, male and female. Using a TORQUE wrench to re-tighten the bolts might be advisable especially if you're not an experienced mechanic as it will (well, should) stop you over-tightening the bolts and snapping them off.

You can buy Torx sockets etc. at AutoZone etc. and you may be able to rent a torque wrench.

Regardless of whether you replace the tensioner or not, be sure to check the idler pulleys. "Notchy" turning or excessive "float" forwards or backwards on their shafts means they're on their way out. Replace them as a set of two not just the bad one..

When refitting the belt make sure to fit the grooved side of the belt on grooved pulleys, smooth side on smooth pulleys, and make sure all the groves in the belt are in grooves on the pulleys.

Finally, remember to put a few drops of BLUE (not red) thread locker on the bolts.

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post #3 of 8 (permalink) Old 03-17-2019, 09:21 AM
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PS a TORX bolt looks like this
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post #4 of 8 (permalink) Old 03-17-2019, 09:25 AM
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A female TORX bolt looks like this. It's a "security" type with the pin in the middle so-say to stop ne'er-do-wells stealing your stuff. When you buy male TORX bits (to fit Female Torx bolts) buy the "security" type which have holes in their ends to accept the pins. They cost a bit more up front but you won't end up having to buy two sets.
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post #5 of 8 (permalink) Old 03-17-2019, 08:18 PM
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Good idea to replace the tensioner when you do the serp belt, especially if over 60k-80k. I think there is a idler as well.

I had to do both of them on my SLK55 at 40k.
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post #6 of 8 (permalink) Old 03-19-2019, 06:28 PM
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My R350 has 190k miles on the clock and as far as I know neither belt nor tensioner no pulleys have ever been replaced. Certainly not by me and I've put 145k of those 190k on the clock.

The CLKs, 350 and 63, on the other hand, needed belts and pulleys at 70k miles. Pot luck I guess...

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post #7 of 8 (permalink) Old 03-26-2019, 06:42 PM
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Tensioner and Idler bearings wearing prematurely related to earlier motors as opposed to the later ones?
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post #8 of 8 (permalink) Old 03-26-2019, 07:17 PM
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Originally Posted by Lioninstreet View Post
Tensioner and Idler bearings wearing prematurely related to earlier motors as opposed to the later ones?
Probably el cheapo parts used during /as a result of / continued use of after the Chrysler era.

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