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  #1  
Old 05-03-2007, 04:10 PM
chetwesley's Avatar
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300SD, 300TD, Why does the alternator have two belts?

I am replacing my alternator in my 300SD. I went to a local rebuild shop, and they had one that was identical, but the pulley is only for 1 belt, not two.

When I look at the car, it appears that the two belts connect from one double pulley to another double pulley. It was the same in my 300TD when I had it. What's the purpose of that? Could I get bye with just one belt?

thanks
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  #2  
Old 05-03-2007, 04:15 PM
winmutt's Avatar
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In case one fails. It also turns the fan. Its one of the few weakpoints of the NA 617...
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  #3  
Old 05-03-2007, 05:01 PM
vstech's Avatar
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The NA 617 has only one belt, the turbo has two. at least on my cars.
two belts give you more surface area to handle the load of the massive 65A alternator...riiiight. OM vehicles tend to get oil on everything. maybe MB decided that slippage might be reduced with the extra belt... cooling is important.
John
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #4  
Old 05-03-2007, 05:42 PM
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Quote:
Originally Posted by chetwesley View Post
I am replacing my alternator in my 300SD. I went to a local rebuild shop, and they had one that was identical, but the pulley is only for 1 belt, not two.

When I look at the car, it appears that the two belts connect from one double pulley to another double pulley. It was the same in my 300TD when I had it. What's the purpose of that? Could I get bye with just one belt?

thanks
Why not just swap the double sheave for the single on the "new" alternator? Very easy for a rebuild shop... RT
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  #5  
Old 05-03-2007, 05:52 PM
chetwesley's Avatar
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Quote:
Why not just swap the double sheave for the single on the "new" alternator? Very easy for a rebuild shop... RT
I would if I could... the nut fell off the shaft and the shaft and pulley were damaged in the process... the alternator is probably fine electrically.
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  #6  
Old 05-03-2007, 06:59 PM
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My daughters 240D has one belt. It broke and so the water pump does not turn. My daughter was stranded on the side of the road comming home from college.

300TD has 2 belts. I had one break and the other one is fine. So the car can be driven and no overheating. I have a new set, I just haven't installed them.

I would install both belts just for peace of mind.

Dave
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1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
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1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
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  #7  
Old 05-03-2007, 08:51 PM
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Two belts is a great idea. The only thing better is a serp.

I had 'matched set' belts on my Merkur. They lasted forever.

If one breaks, you'll make it home. Two belts seem to grip better than one.

You can run a lower belt tension, which is good for the bearings.

Serpentine belts, which are fairly new to me, are fab. It sort of scares me that I might eventually throw one, but so far I haven't.
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  #8  
Old 05-03-2007, 08:57 PM
chetwesley's Avatar
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ok ok two belts it is...

So, anyone have a spare double pulley laying around???
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Sold but fondly remembered: 1981 300TD Turbo Tan 235K miles, 1983 300SD Astral Silver 224K miles


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  #9  
Old 05-03-2007, 10:12 PM
vstech's Avatar
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not exactly a spare, but I have 4 parts cars... pm me.
John
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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #10  
Old 05-03-2007, 10:49 PM
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Its typical Mercedes overkill. Things like that are why they cost more.

Sure you can get by with one V belt, most cars do. But Mercedes takes it a step further, having a second is better. Most cars lack them because such a set up costs more, but the engineers spec'd two because cost wasn't an issue.
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  #11  
Old 05-03-2007, 11:36 PM
Craig
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That double belt has saved me a couple of times, it will run with one, but it will slip unless it's pretty tight. Last time I broke one I was in VT, and I drove around for a week before I had a chance to replace it. Sure beats having to do it on the side of a highway someplace.
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  #12  
Old 05-04-2007, 12:54 AM
JimmyL's Avatar
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Quote:
Originally Posted by jnc19610 View Post

I had 'matched set' belts on my Merkur. They lasted forever.

On a Merkur, the belts surely last longer than the motor.......
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Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John
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  #13  
Old 05-04-2007, 01:00 AM
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Quote:
Originally Posted by Hatterasguy View Post
Its typical Mercedes overkill. Things like that are why they cost more.

Sure you can get by with one V belt, most cars do. But Mercedes takes it a step further, having a second is better. Most cars lack them because such a set up costs more, but the engineers spec'd two because cost wasn't an issue.

Well put!!
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  #14  
Old 05-04-2007, 05:33 AM
Shorebilly's Avatar
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Arrow 2 Belts....

Liebchin....because ve zaid zo........

SB
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Diesels:
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'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
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'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG
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  #15  
Old 05-04-2007, 02:23 PM
Hatterasguy's Avatar
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Also kudo's to Mercedes for making the belts cheap. Last I checked I think replacements were like $10 each!
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-Thomas Jefferson
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Old 05-04-2007, 02:23 PM
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