My dear 65 Amp bosch ALternator locked up, and I couldn't find a rebuild kit, so I put on a "worldwide" brand 55Amp alternator from Advance Auto.

Then my battery went bad so I put in a new battery.

All fine and dandy. Drove away from the store monitoring the new battery voltage - 13.5v. So the alternator was working great.

But ever since I switched the car off after that first drive, the voltage has been dropping steadily. Hasn't gone above 12.4. It's at about 12.05 now after a few hundred miles of driving.

So I figured the alternator is screwed. I started the car and pulled the negative battery cable off the battery - voltage in the car jumps to 13.4 v at idle. To me that means the alt. is working. Right?

When I connect the battery up, the voltage drops to the running voltage of under 12.4v.

What's the deal? Crappy alternator that can't handle any current draw?

The other posibility is that the funky ground fault (I think) I have is causing the alternator to not be able to charge the battery. Basically, when I engage the left indicator and press the brakes, the indicator does a short blip, long pause, short blip, instead of blip, pause, blip, pause.

Also, If I have the lights on and press the brakes, the left indicator console light comes very faintly. And when I engage left indicator with the headlights on, the indicator doesn't work at all.

It might not be related, but when I press the brakes if driving with cruise control, the cruise control disengages and will not rengage until I restart the car.

I know that's a lot of information - maybe some is irrelevant. But it's funky situation and I don't want to replace an alternator if I should rather be fixing a ground fault (which I don't really know how to hunt down).

Any advice for a lazy b%tard?

I'm not an expert but if the stock alternator is a 65A why would you replace it with a 55A. Most people go north of that number not south whenever possible. Also, did you try replacing the voltage regulator on the stock alt? Cheap and easy and works most of the time.
With MB for best results you simply must use original parts. A lot of people like to fight that notion but it's true.

__________________
'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)

Its probaly a faulty ground. Try this. Unplug the instrument panel and see if the voltage issue persists. Sounds like a bad ground in the instrument to me.

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

After going through two crappy rebuilt alternators in a month, I learned my lesson a few years ago and put in the correct Bosch unit.

Dito on that one, I always take the correct Bosch unit, Its worth the extra $ too me. Starter motors as well.

__________________


1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Thanks for the replies.

I would have got a bosch, if I had the time - but the one I had went out almost without warning

The stock on these cars (240D) is 55Amp, and they didn't have a 65 in stock.

Good call on the instrument panel. I'll pull it out and see,.

Then try changing the voltage reg, although the tester said it was OK.

Just for the sake of it. When I needed a new starter I shopped around online, but the best price I found for a Bosch rebuild was at. . .cringe. . .Pep Boys : ~ $86.00 Beat the others by about $70. Could be they've got your alternator too.

__________________
'82 240D, 215,000 +
Classic White, Regenbogen

I'll suggest that you should not pull the battery cable off to test the alternator. This can have bad consequences for the voltage regulator, as in "burn it out".

Ken300D

__________________
--------------------------
1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

Ken - how can I test the regulator? So I know if I've blown it or not?

After a lot of messing around with finding ground faults (which mysteriously resolved themselves), I found what the problem was

The problem was a loose belt on the alternator!

I didn't think that was the problem becuase the alternator was spinning fine, at least I thought it was. THe symptoms are that the voltage is about 12.8 at idle, then drops steadily when revs increase.

I put off adjusting the belt tension becuase I didn't think it was the problem and I thought it would be difficult. BUt it turns out all you need is a 17mm rachet, 15 box wrench and the tire iron. Use the tire iron to lever the alternator out (through the hole in the top mounting bracket).

Hopefully this post helps other people with the same problem.

Actually, there is an adjuster on the front end of the top bolt (at least there should be), so you don't have to pry the alternator with a tire iron to tighten the belt.