Last night past midnight the big coil spring on the serpentine belt's tensioner broke the bottom off allowing the belt to rapidly get chewed up and melted to the idler .

Sigh .

So, I got the call this morning to make his dormant '81 300SD run and now I could use some advice and images as I've never worked on one of these serpentine belt deals ~ how do i re install the spring and belt ? .

TIA ,

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Is this an 87w124 or 81 w123 ? I have 89 w124 and i know its got no spring.

87 603 does have a spring. Now my 87's spring hasn't broken but my 99 606 did. It, pulley tensioner assembly, makes a helluva racket when broken

OM606 Belt Spring

Get one from here, a dealer or if a JY has a 603 or 606 use that to get you by. I'd imagine some other members have ideas about using a shoe string....The spring counter balance's the shock and is under tension when fully engaged, so you are really in a no go sitch till you get a new one.

Be sure to check for damage on the rest of the pulleys in the belt path. A couple, 4-6, months after the spring the broke on my 606 the alternator pulley seized.

Its an easy fix, but check everything else too.

The spring broke on my car last year. Good news is, at the time anyway, a replacement at the dealer isn't expensive.

Note: 606 cars have a clutched alternator pulley. If the clutch fails the tensioner will get damaged in short order. I personally recommend putting the clutched pulley on the 603 cars. If you put on an upgraded alternator it is practically required.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

i've had that spring break on me too. did make a helluva noise. drove it the last mile to the garage with it broken. no other damage. took a spring off a 84 190d 0m601. seemed to be the same part. been working fine for a while now.

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

Instructions on how to change the spring and belt just refer to the manual in the glove box if you have one. Oherwise do a search here it's pretty simple and the spring comes lose when you loosen the assembly to remove the belt

I see i was much too tired to be posting last night, sorry .

The car is a 1987 300SDL , OM603 InLine 6 cylinder Diesel engine .

The belt is melted onto the idler opulley with bits jammed here and there ~ a real mess to clean up .

My primary question is how to install the new spring ? .

New spring from Mercedes is only $46 so I'll likely source it from there .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Get the idler pulley also, fairly cheap and the bearing is a failure item, ... and check the damper/shock for proper operation, check for the dust cap on the tensioner pivot point/bearing, if the bearing is not smooth and tight it needs replacement.

__________________

Gone to the dark side

- Jeff

Thanx Jeff ;

Is there anything else I should know ? .

How do I slack the tensioner to get the serpentine belt on ? .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

DIY - 1987 300D serpentine belt tensioner replacement

Your done with your job by photo 5. Hopefully this will get you going. It is really that simple.

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Treetops
06 E320 CDI 127K Miles
87 300TD 231K Miles

99 E300 269K Miles-Sold

I felt like such a moron not knowing how the tensioner worked. I was cursing (and I mean making sailors blush cursing) the engineer who invented that thing until I figured out how it worked. Seriously a "DERP" moment if there ever was one.

The hole in the spring perch is designed to accept the end of the tire iron out of the tool kit. Makes it really easy.

To make it even easier, print out a copy of the belt routing (google it or search this forum) and take it with you, because the belt routing is NOT obvious, and if you get it wrong, you'll be swearing......A LOT.....

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

THANK YOU ALL so very much ! .

I now know to go get a new damper and idler pulley too along with a new serp. belt and spring .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better