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  #1  
Old 04-27-2007, 11:34 PM
BodhiBenz1987's Avatar
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603 Belt tensioner ... reason for chronic problem?

Well, I was all ready (and excited) to revitalize the sunroof on my 87 300D, and yesterday I go to start 'im up at my parents house and ... nothing. Dad jumped me and I drove it to my mechanic (this was after-hours so I left it there) ... on the way over, radio died, antilock brakes died, lights died, etc. So, yeah, the alternator is dead, confirmed today by the mechanic. What can you do ... it was a crappy aftermarket one as far as I know. I had it replaced within a month of when I first got the car, at a friendly but generic shop near my college ... didn't know any better at that point. So I'll get that replaced, doesn't really worry me. Here's the part that has me thinking ... my mechanic also said the belt is bad and the belt tensioner are tensioner shock are bad and need to be replaced (this guy is trustworthy as they come). According to my records the belt tensioner has a history ... replaced tensioner, pulley, and shock and belt on 9/23/99 at a Goodyear ... replaced tensioner bolt on 8/20/01 at MB dealership ... replaced belt tensioner and belt on 5/27/03 by my current mechanic. The car was given to me in July of '03, so all of these things were done when my dad had the car. He thought it was curious that the tensioner needs to be replaced again. So, what I'm wondering is, is this indicative of another problem? Is there a reason for chronic belt tensioner issues? Unfortunately I do not know the details of the former part failures, just what work was done. I suppose the latter need for replacement could have been a result of former shoddy work (the Goodyear is a hit-or-miss deal as far as my experience has been). Just wondering if anyone has any thoughts.

On a side note ... a whiney side note ... I'm feeling very inadequite for not being able (or willing, or a combination of the two) to do this myself. I'm reaching that point where there's no reason I should be paying labor for things I can do myself. My mechanic really does his best in terms of giving me a break on labor, but his time and his assistants' time isn't free. And more importantly than the money, I love the sense of pride that comes with doing my own stuff. For this one, there's not much I can do. I have no garage and no time in the near future, and I'd rather swallow my pride and a big bill and have the car in working order than leave it sitting for a month until I figure out how to do it. But I think in the future I am going to be a little more daring. No point to this rant ... I just wanted to put my self-butt-kicking in words.

Any theories on the tensioner debacle?

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)
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  #2  
Old 04-28-2007, 12:43 AM
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No, but I just put in a new upsized alternator. The job wasn't bad at all. Potomac German has used 140A alternators for about $100. The one I got was in very good shape. Also, if your mechanic is doing the alternator you may want to think about putting in a new thermostat as it is right there and a bit easier with the alternator out of the way.

This is the kind of thing that would be good to tackle yourself as it is pretty straightforward. You could do the alternator from the top although it is probably easier from the bottom. It is right in front though so you could probably do it without even jacking the car. The only downside to putting in a 140A altenator is that you would want to replace the wiring as well. This isn't a big deal but adds some fussiness to the procedure. Doing the tensioner is also pretty easy. Make sure that you put in a mercedes tensioner rather than aftermarket. It could be that you just have been getting mediocre parts. Not likely Goodyear put in a mercedes part. Maybe not even your indy. Good luck.
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Old 04-28-2007, 04:46 AM
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Location: Walnut Creek, CA & 1,150 miles S of Key West
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My 606 shares the same tensioner and motor mount design as your 603.

A partially collapsed left motor mount on mine manifested as vibration at the tensioner which caused a couple damper shocks to overheat, a spring to break, a pivot arm to fail and a couple of belts to stretch.

Look at the tops of the mounts with a bright light for any separation or cracks. You should have a minimum height of 13mm measuring from the top rubber rim down to the next lower rim. Use a bolt head to measure with.
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09' Hyundai Santa Fe Diesel 48k (S.A.)
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  #4  
Old 04-28-2007, 06:00 AM
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Before you buy a new alternator you may want to take a look at the voltage regualtor. The brushes may be worn out. It is much cheaper and easier to replace. $25 part and two phillips screws. I'm sure you could do it in 10 min. I beleive Diesel Giant has a "how to" on his website.

Regarding the tensioner, one of my 124's (Fritz) is on his second known tensioner (my records only go back to 150K) and it needs another one now. I am not sure if it just needs the shock or the whole setup. I wish I could find a "how to" for that also.
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  #5  
Old 04-28-2007, 06:43 AM
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That poor tensioner seems to get quite a workout from the belt and other things the belt pulls. For some reason, the tensioner on these engines just doesn't last the way it does on my GM engines. I think there may be two factors at work, 1) the diesel MB engine seems to put a lot more vibration and shock into the belt, and 2) the tensioner design seems mechanically weaker than other designs.

I broke a timing cover shortly after a tensioner and shock change on my 87 300D. The new shock was a LOT stiffer than the old one, and I feel it stressed the aluminum cover a lot more, resulting in it cracking and breaking open. The new timing chain cover has a stronger design, possibly due to this issue. I have yet to take the challenge to fix the car, but it needs to be done this year.

Since the design is weak, there is nothing you can do but watch it closely and when it goes out, replace the parts with quality parts.

Ken300D

Carfax is $25 for 30 days. Autocheck is $25 for 60 days.
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  #6  
Old 04-28-2007, 09:52 PM
BodhiBenz1987's Avatar
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Quote:
Originally Posted by TMAllison View Post
A partially collapsed left motor mount on mine manifested as vibration at the tensioner which caused a couple damper shocks to overheat, a spring to break, a pivot arm to fail and a couple of belts to stretch.

Look at the tops of the mounts with a bright light for any separation or cracks. You should have a minimum height of 13mm measuring from the top rubber rim down to the next lower rim. Use a bolt head to measure with.
This could be a factor, as I had the motor mounts replaced in 2005 ... one was really bad and the vibration was pretty fierce. Current tensioner has been in there since '02, so it could have been affected during its time with the old motor mounts. Guess I'll have to wait and see how long the new one lasts.
__________________
1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)
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  #7  
Old 04-28-2007, 10:39 PM
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Quote:
Originally Posted by BodhiBenz1987 View Post
This could be a factor, as I had the motor mounts replaced in 2005 ... one was really bad and the vibration was pretty fierce. Current tensioner has been in there since '02, so it could have been affected during its time with the old motor mounts. Guess I'll have to wait and see how long the new one lasts.
Measure it, see where it's at....if you dont have a 13mm bolt, find a socket that fits snuggly inside of your 13mm socket. Will probably be your 9 or 10mm. Use it to measure with.

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09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)
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