84 300 td wagon - PeachParts Mercedes-Benz Forum

mofarmer · #1 10-29-2006, 07:23 PM

This thing is an alternator killer. It just did in the 5th alternator in 5,000 miles. After the first one quit I went to Auto Zone and got a replacement, it soon died, so I ponied up more money and got the larger size one, it lasted only a few weeks. I took it back and got another, it died and I took it to a mechanic who put on a fourth one and checked things out and couldn't find anything wrong. That lasted for a couple months. I thought maybe it was the AZ alternators so I swallowed the expense, located an overpriced Bosch in KC drove over 400 miles round trip to get it, put it on....it lasted 150 miles. It was working fine when we came home last night, not working when I started it this morning. There's never a warning, they just quit, no electrical smell, no apparent malfunctions, nothing. I have talked to the mechanic at the local MB dealership he had no idea what could be causing this problem. I liked this car when I first bought it, but I am sick of having to constantly work on it, and spend money on it and being afraid to drive it anywhere. Before I dump this thing and loose my butt on it, does anybody have any suggestions or ideas?

84 300 TD WAGON
mofarmer

vstech · #2 10-29-2006, 07:52 PM

all theese on the same battery? starters can draw massive amounts of power, batteries can draw similar amounts. a battery can have a plate with a sometimes short... starters can have shorts on a portion of the winding. the alternators in theese cars don't have much to them. they have internal regulators, the output goes to the battery, the charge signal goes through the warning light, to the battery. a bad warning lignt can cause an alt to seem bad when it is not.
are the alternators actually bad when they change out?
ok, it is also possible that you have gotten what 4 bad alternators. the bosh being bad seems odd. keep us posted.

F18 · #3 10-29-2006, 09:48 PM

I had one remanufactured alternator fail in about 60 miles on a jeep once....but to have 4 prematurely fail seems impossible unless something is wired up in reverse polarity and or the system is not properly grounded.
Has anyone identified what exactly is failing on them? ie. voltage regulator
core windings.......

Start by checking for proper negative and positive connections with the battery and starter if you have not done so. Check all ground connection on the body. It would not hurt to add another heavy ground cable from an engine block stud to the front sub frame.

Refresh my memory......were the alternators on the 84 300 TDs one wire or two wire?

#4 10-29-2006, 10:00 PM

First of all, stop throwing parts at it (Even worse, the same part).

Test your battery, check for short circuits, make sure you ar installing the alternators correctly and make sure the belts are not too tight (1/2" defection).

Also, do you have a big subwoofer system and/or amp?

mofarmer · #5 10-30-2006, 08:27 PM

Thanks for the replies. The only thing that has kept this bearable is that the AZ alternators have a lifetime warranty so they are replacing them at no cost.

I have taken the dead alternators to a parts house with a test machine and both both the alternator and regulator were shot, I stopped by on the way home from KC and had them check the used Bosh, it was working as it should.

I installed a new, correct size, battery after the second alternator, it checks out okay. I have wire brush cleaned the connection points, checked for correct polarity, and shorts, and correct or loose connections, there is proper tension on the belts, everything seems to check out ok.

The only non factory electronics are the volt meter and a Sony radio/tape/CD player, the speakers are original equipment.

F18 there are 3 wires fastened into a push on clip. I will try this one more time, get the latest AZ unit replaced and try your suggestion of another ground strap.

Thanks to all,

mofarmer

#6 10-30-2006, 08:39 PM

I was also going to suggest checking the connections and grounds.

I have not had very good luck with McParts rebuilt alternators in my 300D either. A couple of years ago my original (I think) alternator failed on a weekend and I replaced it with a generic rebuilt. I took the car on a couple 1000 mile trip and the rebuilt failed completely. I limped home and returned it for a replacement, and went out of town again, this time I made it about 1000 miles (to Chicago) before it failed. I found a indy mercedes shop in Chicago and he put in a Bosch, that one has been doing fine for over 100K miles (with some new brushes). I'm done with cheap rebuilt alternators.

babyjames · #7 10-30-2006, 08:47 PM

Is anything coming into contact with the body (housing, call it what you will) of the alternator itself? I had a 242 turbo Volvo that went through a couple alts. before I realized the oil-pressure-gauge sending unit was touching the alternator just enough to fry the rectifier.

Also, maybe try re-wiring the alternator itself. You can ditch the black "plug" part, at least temprarily, and just use spade-style crimp-on connectors on the terminals of the alternator. Use some nice, heavy wire for the two big plugs. If the individual connectors in the plug are shot, they will not make proper contact, which could lead to premature alternator failure.

What is the output, at the bus bar, of the alternator after installation? Is it kicking out 14 volts? At the battery?

Jay.

mobetta · #8 10-30-2006, 11:36 PM

ahh- just sell me the car cheap. i need a parts car

good luck.

vstech · #9 10-30-2006, 11:44 PM

Yeah, let me know if you decide to dump this baby, I would love a turbo TD. I have enough parts cars to make yours run indestructibly.

John