PeachParts Mercedes-Benz Forum - Drive belt tensioner failure analysis

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Quote:

Originally Posted by nglitz

My 260E has an idler pulley above the alternator. As an alternative to removing the lower alternator bolt, I removed that idler pulley. It looks to be identical to the puller on the tensioner. There's a plastic cover over the front of the idler pulley and then an internal hex bolt to remove (Allen wrench). After a new belt, the idler pulley can be re-installed by catching the tip of its bolt in the hole and then using the Allen wrench to pull it into position before starting to turn the bolt. Obviously care needs to be taken to avoid stripping the idler's bolt in the process of re-inserting it.

When I first did this in the process of installing a new belt (that probably wasn't really needed) I could watch the tensioner needle swing right up the ramp. A week later, the tensioner died on me and needed replacement. I ran it for a week with a dead tensioner (maybe 200 miles total) and not a squeek. The new belt and the way it wraps around the significant power users (alternator, water pump, A/C compressor) probably help.

OTOH, my daughter's '94 Ford Taurus has the world's simplest serp. belt tensioner. One spring and the tensioner arm has a square hole for a wrench handle. Pull the arm back, swap belts and release the wrench handle. Hard to imagine anything simpler.

Yes, the simplest and best belt setup I ever saw was on an 85 Mustang GT 5.0 V8. It had a spring loaded tensioner and a serpentine belt. You could lever the tension with a tire iron, big screwdriver, crowbar or whatever you had lying around. I think that in a race I could change one of those belts in two minutes.

That was definitely a case where Ford "had a better idea."

I have an '88 Vette that is changed the same way except you use a 1/2" breakover bar and it is harder to snake the belt off and back on.

Have a great day,

Sorry Duke,

Tensioner thrown out week before last.

Drive belt tensioner failure analysis- DUKE2.6??

Duke,
your analysis on the belt tensioner from July 2005 is the best I've seen. One point that I need clarification on though is in your item #6 when you say:

"...then set the pointer at the bottom of the ramp.", and then when you turn CW that the "pointer begins moving up the ramp."

I am unclear what direction the ramp is. If you are saying that the needle moves "outboard" (to the right, vewing from the front), then is that not in conflict the service procedure (13-3420 in the M103 service manual) which shows the pointer "outboard" in the v-belt slackened position?

Can anybody shed light on this point?

My greasy hands and driveway full of parts await... :huh:

Thanks, Mark
1990 300te

Never had a problem untill the belt was replaced, it failed. At 25000 more it failed again (the replacement) no they have not improoved it.

Quote:

Originally Posted by Peter Guenther (Post 1493695)

Never had a problem untill the belt was replaced, it failed. At 25000 more it failed again (the replacement) no they have not improoved it.

Peter:

Was the second failure also occured when you replace the belt?

I am going to replace the belt on my 300E this summer and will use the alternator as the pivot. Will leave the tensioner alone.

My tensioner is making a squeeking and rattling noise sometimes on startup. Weird, however, the tension on my belt is very tight to the point I believe it is too tight.

Reading this post, I've attached 2 pictures of what I believe are tensioners that would work on my car based on model year part lookup. Correct me if I'm wrong about applicability. Right one is an SKF and the Left one is Dayco. The interesting thing about the Dayco is the decription:

DAYCO BELT TENSIONER -- Automatic Belt Tensioner, The Featured Patented Flat Spring Design Reduces The Risk Of Accessory Bearing Failure, Reduces The Risk Of Belt Squeal And Slippage, Or Poor Accessory Performance Caused By Low Tension, The Flat Spring Is Coated To Resist Rust, Heavy Duty Cast Aluminum Spring Case Resists Cracking, Heavy-Duty Cast Aluminum Arm Offers Additional Strength And Less Distortion

Is the "Flat Spring Design" what has been mentioned as what would be an improved design or is this the same design as the original?

Good post. The next question is whether anyone has any experience with this type on tensioner on a Mercedes in place of the original.

Quote:

Originally Posted by LarryBible (Post 944164)

As I recall, my 1984 190D 2.2 Diesel had a simple spring type tensioner. It was extremely easy to replace the belt and no rubber tensioner to break. All you had to do was insert the round end of the lug bolt wrench into a whole to release the spring tension. Great design!

When I purchased my 1993 190 2.3 new, the belt tensioner lasted less than the original serpentine belt. The rubber bushing was torn/broken. Since that time, it seems like most of my parts replacements are due to rubber/plastic failure. Linkage shifter bushings, drive shaft flex discs, sub-frame mount bushings, motor mounts, plastic radiator neck, etc.:furious2:

A friend of mine that owns an independent MB repair garage puts it this way..."The things that make a Mercedes a Mercedes are going to fail".

On another note, I feel that my '93 190E has been a great car and has been easy to maintain, parts are always available, and if they are not in stock I can get them the next day. As I wonder if MB quality has improved or gotten worse, when I compare age, mileage, parts replacement, paint quality, and interior quality, my 2001 SLK has been a big improvement over the 190E in that respect.

>>Is the "Flat Spring Design" what has been mentioned as what would be an improved design or is this the same design as the original?<<

Does anyone have any information on this?

Also, is it advisable to replace the pulley at the same time as the tensioner? It looks like they are sold as separate items. In my case, the car only has 30,700 miles. I am getting a short rattling sometimes at startup and then again for a short time the majority of the time the air-co compressor kicks in (2.3L w202).

Both of the tensioners I replaced on my W201 came with pulleys.

Unfortunately, it appears they are separate items to replace on the w202 according to the online part sellers I checked.