Hi, looking for some help with what I think is a belt tensioner problem on an '87 300d. I bought the car out of Charleston SC with 170,000 miles - a really clean car. After about 400 miles on the trip home (to nw pa) I noticed a chirping sound under the hood. I thought it was the alternator, but when I sprayed penetrating oil on the tensioner it went away. I replaced the tensioner and idler wheel, and the bearings on the tensioner were rough. After a day or two, the chirping sound is back - intermittently at this point. When the belt was slack I spun all the pulleys and nothing feels bad, maybe the alternator bearings are a little rough, but not bad enough to chirp. What else is left to change? I'm no certified Mercedes mechanic but can usually resolve my own problems like this. Is there something I'm missing? Thanks.

That sounds like an old belt and as long as they are, you will notice a LOT of stretch if you hold it up to a new one. It might also be the time to replace the tension spring and shock/damper (that work along side each other) at the black tensioner lever. When those are bad you hear a louder chirp like sound.

With the engine running, push down on one side (then the other) of the lever. If it gets quiet - problem defined.

BTW you CAN get a new belt in without removing the fan or a single pulley but you will need time and the patience of a Zen master.

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1987 300D (230,000 mi on a #14 head-watching the temp gauge and keeping the ghost in the machine)
Raleigh NC - Home of deep fried sushi!

I had the same problem and it was the shock/damper

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Pete.

I'll replace the belt and the spring and damper - all with far less than zen patience. Thanks for the advice - am new to these mercedes and love them to death - but can honestly say whoever came up with this tensioner design was definately having a bad day. If that's the worst thing you can find to say about a car that's still not too bad. Someday perhaps, I'll have an answer to one of these questions instead of just asking for help. Taking me a while to get my mind wrapped around these german diesels. I'm still a work in progress. Thanks again.

No kidding on the tensioner.

Is there an easier way to manipulate the tensioner? It looks like one would pry against the water pump housing, ... that can't be right.

(upgrading the alternator tomorrow morning)

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Gone to the dark side

- Jeff

Definitely the wrong way. It wasn't too hard to manipulate the one I had but I no longer remember how it was done. I also had the chirp. I used belt dressing on mine and that cured it.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

by manipulate are you talking about relieving pressure to remove the belt?

If so, get a 6"(or longer) 3/8 extension and a 13 mm socket and wrench, put the extension in the hole in the plastic spring holder (top center of front the head) loosten the 13mm nut, apply downward pressure to the plastic piece to remove the long bolt and release the spring tension. Remove the spring. At this time you should be able to manipulate the tensioner by hand without the need for "prying".

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Dean

Thanks Dean & DJ.

I did find the method, as Dean described, in a parallel thread. Haven't done the alternator upgrade yet though, staring at me from the shelf until I get do West Marine for some cables and terminals.

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Gone to the dark side

- Jeff