Do I dare replace my alternator? - PeachParts Mercedes-Benz Forum

arnoneh · #1 02-03-2010, 10:49 PM

My alternator is not generating juice even after replacing the voltage regulator. I replaced alternators in old 70s US cars when I was a kid but I noticed some threads here about people having problems replacing their alternators.

My car is an '85 300D turbo wagon. Seems like it should be straightforward: remove wires , loosten bolts, remove belts, remove alternator. Reverse. The only thing that might cause me problems is getting the belt tension right.

What complication am I missing in my simpleminded approach?
How do I best get the belt tension right w/o the special measuring tool?

thanks -Harv

pawoSD · #2 02-03-2010, 10:55 PM

It can be a pain to work on the alternator on the 617 engines, especially if the bolts are real tight or if the tensioning bolt is bent or rusted etc...

clm · #3 02-03-2010, 11:39 PM

Take off the entire top bracket-Leave it on the alt and disconnect it from the engine- this way you will not mess up the tentioning bolt- like almost every one I have seen

. Look at it and you will see what I am talking about.
Rest is very strait forward...

hey_allen · #4 02-04-2010, 12:34 AM

I'll second what CLM just said, it's easier to get the tension bolt off once the bracket is off the car, as it ends up with more clearance to pass the end of the small threaded part.

If you figure out what was wrong with the starter, please let us all know.

I just got done replacing the one on my 300SD, after finding that one of the commutator rings was missing a third of it's surface, which had peeled off and wadded up into a ball that was trapped in the back of the alternator!

compress ignite · #5 02-04-2010, 02:59 AM

Simple Straightforward.
(Ignore the Alternator Removal Instructions,unless you're driving a V-12)

I like the Alternator Parts Replacement instructions from V-12 Uber alles:
http://www.v12uberalles.com/Alternator_Bearing.htm

(WAI Global is an Electrical parts supplier to the "Trade")
WAI is a seller to wholesale accounts ONLY,Your electrical reman shop can order the bearings for you.
OR you can order them from the Mercedes dealer (At a premium price)['Cause they have both the Bosch and Mercedes Imprimatur]

Ask Phil for them!

http://search.waiglobal.com/prodsubcat.aspx?prodcat=Alternator%20Parts

They're showing a "Standard" Alternator @ 55 Amps.
And an "Optional" @ 65:
http://search.waiglobal.com/vehiclelookup/vehichlelookup.aspx

These are all the parts available for the 55 Amp Alt:
http://search.waiglobal.com/vehiclelookup/bomsearch.aspx?search=bom&part=0-120-489-918
(Click on the BLUE part # and then click on the Individual part #)

layback40 · #6 02-04-2010, 04:07 AM

Its a simple process to remove the alt. The hardest bit is deciding what alt to replace it with! Direct replacement or do you upgrade.
Once you have completed the task, you will wonder what all the fuss was about.
Good Luck & Please let us know how you get on!!

tr1cky · #7 02-04-2010, 09:34 AM

Ditto. The alternator is not a bear. The tensioner is a bit tricky, but simple once you understand how it tightens.

My advice, if you're going to get in there and do that, replace all of your belts while you're at it.

Conti-tech belts.

John Schroader · #8 02-04-2010, 10:18 AM

I agree with these guys. It's pretty straighforward in both my '83s. Like most things on these cars, it makes sense once you look at it. What can't other cars be so straightforward?

Maki · #9 02-04-2010, 11:02 AM

I may be pointing out the obvious, but are you sure the "exciter" circuit is delivering current to the alternator? You might want to verify that before pulling the alt.

chasinthesun · #10 02-04-2010, 11:17 AM

Make sure its the alternator first and not a bad ground wire, just replaced one and the idiot light still would come on periodically .Looked over at the old neg cable and noticed snug bolts but the wire was loose in the eyelets ,Wiggled the wire then checked my dash light ,all good .A $125 expense I probably could of fixed with a $5 neg wire.The alternator still looked old ,so a future project got done a little early.

Nate Stanley · #11 02-04-2010, 11:22 AM

and your charge light indicator bulb is part the exciter circuit. If it's burned out, the alternator will not charge.

LUVMBDiesels · #12 02-04-2010, 11:58 AM

You can replace the alternator with a Bosch AL129x which is a 115 amp unit. It is a direct bolt in, but you need to modify the leads going from the alternator to the junction box on the fender.

Do a search for AL129x and you will see what I mean.
http://www.peachparts.com/shopforum/showthread.php?t=93569&highlight=upgrade+alternator

They are available on Saab 9000's in the bone yard (among other cars) or are usually on ebay.