The car wouldn't start this morning. I just got finished jumping it to get it started and checked out the charging system with a meter. The meter says that its 12.4v...too low. With the lights and heater blower on, lowers it ever further to 11.6v. The belts are tight and both the battery and alternator were replaced in January. I really don't feel like just throwing parts at it, (another alternator) what other choices do I have?
84 mb 300sd.


Thanks Dan

Did the new alternator come with a new regulator or did you slide the old regulator into the new alternator?

Sixto
87 300D

Dan,

Was the alternator actually "new" or a rebuilt unit?

In any case have the charging system checked - most service places can do this for you (Pep Boys, Sears, etc.) and tell you what the issue is. If it is the alternator, you may have a warranty claim. If not, don't buy from the same place again.

Rebuilding alternators is a cut throat, somewhat sleazy business. For the most part a good rebuilt job is limited to the mechanical stuff, like bearings and the surface the brushes ride on being trued, and maybe a cleaning of the windings, respray painting the exterior, new voltage regulator and maybe a test.

Nothing is typically done to the windings themselves other than cleaning them with a solution, and nothing is done to the rectifiers unless the testing shows one or more failed components (diodes). This leaves you with a "rebuilt" alternator with some sketchy essential parts. I have used a local rebuilder a number of times who runs a before and after test, and routinely changes the diodes. If the machine fails the hot megger check, that means the at temperature performance of the winding insulation is gone, and he doesn't give you the unit back until he builds you a "Frankenstein" alternator with windings from another one that are good. None of the smaller rebuilding places actually rewinds the machines and I don't believe any commercial rebuilding shops check insulation resistance at operating temperature.

So, if you buy a new alternator, that is actually new, it has new windings, and new everything. A rebuilt unit is mostly an unknown assembly of new stuff that is likely good and old stuff that is in unknown condition. So don't be alarmed if the machine has another failure shortly after being installed.

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)

The only thing about those rebuilds though is that sometimes, for example at our local small parts counter where we get a lot of stuff... it's pretty much free lifetime replacement. So you can go through four or five of them and only pay for the first one.

You just have to decide what "inconvenience cost" adds up to.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

I think that I may have reused the old regutlator, but I'm not positive. I will replace it in the morning though. Thank you all for your help.
Dan

I believe the rebuilt alternator would come with a regulator as it is an intergral part of the alternator assembley from a rebuilder. It is also quite common to get a bad rebuilt unit as most the so called rebuilding is done where labour and quality control efforts are pretty low.
For example a large chain store operation closed down all it's canadian rebuilding and went to mexican rebuilt replacements. I never buy them anymore since trying them a few years ago. They were terrible.
We have a couple of rebuilders from california regularily on ebay. They have perfect feedback and very reasonable prices and shipping from california. .Also you do not have to send a dud in. I think they charge about 50.00 for a rebuilt alternator plus about 20.00 shipping.
Seem to sell quite a lot of older mercedes rebuilt starters and alternators. I think they intend to stay in business.
I always try to support the firms trying hard to satisfy people. The good prices do not hurt either. As long as they survive it tends to keep the competitions prices down as well.

If your tests are all at idle, it is normal. The M-B manual tells you that you should not idle with lots of electrical accessories such as rear-window-heat + lights + blowers et al or it will discharge the battery.

__________________

Gone to the dark side

- Jeff