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  #1  
Old 03-15-2002, 07:41 PM
benzat
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altenator

how can you tell an altenator is going to *lock up*?

had mine replaced the mechanic told me it was locking up I do know wht belt is connected to the water pump.

what would the symptoms be for trying to lock up?

benzat

1982 380 SEC
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  #2  
Old 03-15-2002, 10:33 PM
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Location: Old Lyme, Connecticut
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benzat,

The symptoms should be belt squealing, and possibly a lower than usual engine idle speed. As the condition develops, it usually becomes fatal (for the alternator) very quickly, as the added load in the bearings quickly causes them to get hot, which adds load, making them hotter, and so on. If it gets hot enough, the bearing material melts, and that leads to a seized shaft pretty quickly. The old alternator should have been difficult to turn by hand after the belt was removed or after it came out. Hope this helps, Jim
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1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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  #3  
Old 03-15-2002, 10:44 PM
benzat
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yes that does help.

I got it replaced but Ive never heard of one locking up

thanks again

benzat
1982 380 SEC
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  #4  
Old 03-15-2002, 11:30 PM
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Join Date: Jul 2001
Location: Old Lyme, Connecticut
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benzat,

I can't say I have seen one seize either, as an alternator usually fails due to brush wear or some other electrical event. Tightening the belt too much can overload the bearings, and begin the process, but the brushes usually can't handle the extra movement of the shaft as the bearings wear.

If your mechanic said it was about to lock up, the problem was well along, and it is feasible you might have heard some extra noise from the alternator. Then it is also feasible that whatever caused the problem, if it was not the belt being overtight, just happened and you found it. Other causes might have been getting water in the bearing (flood, or going into a deep puddle, or worst of all, driving on the beach and getting saltwater in there), or developing an electrical problem on the rotor that passed current throught the bearings. You never said why you took the car in and had the alternator examined and ultimately replaced though, so this speculation is kind of ungrounded and likely not of value.

Jim
__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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  #5  
Old 03-16-2002, 09:56 AM
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I had one lock up on an 82 Chevy v6 diesel. That engine had a serpentine belt, which wrapped around the alternator pulley about 270 degrees, putting tremendous pressure on the alternator front bearing. (This POS would eat alternators about every 20k miles). Anyway, it locked up without breaking the belt, which stalled the engine, but I was able to coast into a friends body shop in neutral. When we popped the hood, the alternator was actually on FIRE! For a few minutes, there were 3 guys taking turns spitting on the alternator trying to put the fire out, until a fire extinguisher appeared from somewhere.
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  #6  
Old 03-16-2002, 11:24 AM
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The obvious reason that you have not seen a locked up alternator is that you are not in the trade.

Bearing failure is a common form of alternator failure and it is fixed simply by replacing the bearing, if a skilled technician listens to the motor in the last few thousand miles before it locks up. Picking up the noise in bearings of any of the accesories of a modern motor (including belt tentioners and belt idlers) is one of the reasons for paying an experienced tech to service your car.

Cars I service don't lock up alternators, cars I repair do.
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  #7  
Old 03-17-2002, 10:54 PM
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Location: LEMONT-CHICAGO
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I had an alternator lock up on my 85 Mustang GT. I had a close encounter of the third kind with the dash lights flashing on and off. I popped the hood and the serpentine belt snapped and there was smoke coming from the alternator.
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