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ML430 wanted to tell me something - belt tensioner

3K views 9 replies 7 participants last post by  PCar SBO 
#1 ·
So for the last 4 weeks the engine kept making this high-pitched note when reving up that sounded somewhat unusual and new. I once even looked under the hood trying to track it down. It sounded like a squealing bearing, but never did anything about it and eventually forgot about it.

Last night I got the dreaded call from my wife:" The car doesn't work. It can only go straight but the steering isn't working at all and I have a red light with a + and - sign on the dash"

I first thought maybe the hose from the power steering pump to the cooler jumped off. So I asked her if there was a puddle of fluid under the car. She said yes. I considered buying some power-steering fluid before heading out but then it hit me: Alternator light and no power steering can only mean one thing - the belt.

The serpentine belt jumped off because the pulley for the belt tensioner was wobbling on a disintegrated bearing. Even spewed out some metal filings. Now I know what the squealing sound was. :) The car has 140k miles and this seems to be the original belt. The tensioner still has the star nut in the center and the metal wheel.

The good news: For less than 140$ I have the fan clutch wrench set, new tensioner, new idler pulley, and new belt on its way. Looks like a doable DIY job.
 
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#9 ·
Mine was in for state inspection Thursday last. I'm talking with the shop owner up front when the inspection guy bursts in with "Your engine is smoking badly!"
The tensioner pulley had seized, burnt the belt [=smoke] and eventually thrown the belt, all while idling in the inspection bay.
Got the parts the next day and replaced the tensioner, idler pulley, and belt. All good now. I did it in the shop parking lot without a jack, so its not really a challenging job.
This will horrify some, but I didn't remove the fan or shroud. That was fine until removing the idler pulley and discovering that the bolt is waay too long to come out with the fan in place.

You may want to stop reading at this point. Faced with a trip home to get my thin 36mm wrench and clutch holder, I borrowed a die grinder and gently relieved the base of two blades [one leading edge and one trailing edge] which allowed the bolt to come out nicely. Should be a required mod!
 
#10 ·
Quick update: The parts arrived while I was away on a business trip. The wife had to put up with a rental car for the time being.

When I got back this weekend we went out to the parking lot with a bunch of tools and a flashlight to attack the issue. The fan and clutch came off easily with the special holder and 36mm wrench. This gave me enough access to get everything replaced. I did not remove the shroud since I couldn't figure whether there were screws or whether it was just held by the clips.

It took less than 30 minutes to get the old tensioner and idler pulley off and everything installed. The most difficult part was to install the lock pin blind while tensioning the mechanism so I could get access to the lower mounting bolt.

During the first go I miss-routed the new serpentine belt and started questioning whether it was the right size. I had to re-install the lock pin on the tensioner and re-route the belt correctly. Then everything fit just fine.

The car runs great and the funny noise is gone. The new tensioner wasn't made by URO, it was some other brand. Forgot the name, its short and starts with a C. We'll see how long it lasts. The total cost was 133$ for the parts plus the tab for the rental car while I was gone. All in all a very easy fix with the right tools.

Ingo
 
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