Alternator rebuild? - PeachParts Mercedes-Benz Forum

cirrusman · #1 09-02-2010, 03:35 PM

So I've got no charge from the alternator. However, the alt light is not coming off (might be the light bulb, I don't know, I'll have to check). I installed a new regulator 2 months ago, so I know that's not the issue, and I checked that just now anyways. I'm thinking about putting on a rebuilt alternator, but before doing that, I'd like to try and rebuild the one I've got. Anyone knows how to, or knows where to find a website on how to? I checked some websites, but they're doing GM, Fords and the like, and I've not found DIY threads here...
Many thanks in advance

Diesel911 · #2 09-02-2010, 04:50 PM

I have taken my Mercedes one apart and replaced both of the Bearings and done to same on American Alternators. However, I have never trouble shot any Diodes in them.

Ounce the Alternator is out of the Car take it to have it tested to see if it is bad. At Auto Z or someplace similar they will only be able to tell if it will not charge.

(Also there are things that could kill a good Voltage Regulator. May be there is a local member who would loan you one to see for sure if it is the Voltage Regulator or not.)

What I can recall is that I used an Impact Wrench to remove the Alternator Shaft Nut.

Remove the Voltage Regulator.

I had trouble getting the long skinny screws/bolts that held the Alternator togetner out. As 2 were siezed in.
I did not have any trouble doing what was needed to remove the Front Casing of the Alternator.
However the Front Bearing was reluctant to come off and I used a Bearing (separator) Plate in conjunction with a 2 jaw Gear Puller to remove it. Of course you can leave the Baring on and just pull the Rotor Out.
Ounce the Rotor is out you can do the same continueity test that is done on other types of Alternators with your Ohm meter on the Slip rings. If I remember correct you should not get any conduction from a slip ring to the actual shaft; only from Slip Ring to Slip Ring.
Since I went no further that to remove the other Bearing In cannot comment on how to get the Statator out or how to test it. I would imagine it tests the same as other Alternators do.
from my notes
BOSCH ALTERNATOR STUFF
http://www.humanspeakers.com/audi/alternator.htm
http://www.rangerovers.net/repairdetails/altrebuild.htm
Illustrated proceedure
http://www.rangerovers.net/repairdetails/electrical/boschaltrepair.htm
http://www.ratwell.com/technical/Alternator.html
BOSCH ALTERNATOR PDF
http://www.passat32b.hu/olvasnivalo/kezikonyvek/szervizhez/FeszultsegszabalyozoAlternator_Regulator.pdf

cirrusman · #3 09-02-2010, 05:20 PM

Wow, that's pretty awesome stuff, thanks for your reply!

tangofox007 · #4 09-02-2010, 06:17 PM

Unless you know that your problem is the regulator and/or bearings, you are probably better off buying a Bosch-rebuilt alternator. (Not to be confused with a rebuilt Bosch alternator.)

cirrusman · #5 09-02-2010, 08:53 PM

I actually don't know what the problem is... it could be the wire from the alt to the battery... I'll check that too. I do know for sure that it's not the regulator though.

Diesel911 · #6 09-02-2010, 10:48 PM

Quote:

Originally Posted by cirrusman

I actually don't know what the problem is... it could be the wire from the alt to the battery... I'll check that too. I do know for sure that it's not the regulator though.

If you look at the Alternator Connector there are 2 large slots the go to 2 fat red wires. Both of those have Battery Voltage all of the time.

The smaller slot has a Skinny Blue Wire; that is the Wire that goes to the No Charging Light. That wire only has voltage when the Key is on.

After that there could be a issue with the ground. If you pull your Voltage Regulator off you will see that where one of the screws goes through there is an area that grounds on the Alternator Casing. You might scrap any oxidation off of the Alternator Casing around the screw hole to make a better ground.
After that some have recommended using 1 Jumper Cable from the Negative Battery Terminal and touching the Alternator Casing/Housing so you know for sure it is well grounded to see if it charges.

funola · #7 09-03-2010, 07:27 AM

Quote:

Originally Posted by cirrusman

So I've got no charge from the alternator. However, the alt light is not coming off (might be the light bulb, I don't know, ...
Many thanks in advance

If the light is not coming off, that means it was on, that means the bulb is good.

Diesel911 · #8 09-03-2010, 01:25 PM

Quote:

Originally Posted by tangofox007

Unless you know that your problem is the regulator and/or bearings, you are probably better off buying a Bosch-rebuilt alternator. (Not to be confused with a rebuilt Bosch alternator.)

Off subject but when I removed my Alternator to change the Bearings it had a Rebuilt by Bosch North America sticker on it.
I was surprised to find that the Bad Bearings I removed from it were Made in China.
Since I got the new Bearings really cheap on Ebay I just replaced them with another set of Made in China Bearings.

compress ignite · #9 09-03-2010, 01:52 PM

Or Wagner.
http://www.wagneralt.com/

Most Fav-O-Rite ALT repair Post:

http://www.oichan.org/mods/alter/alter2.htm

2nd Fav-O-Rite ALT repair post (Thanks to BA @ V-12 Uber Alles):

http://v12uberalles.com/Alternator_Bearing.htm

cirrusman · #10 09-04-2010, 11:21 AM

Quote:

Originally Posted by funola

If the light is not coming off, that means it was on, that means the bulb is good.

Sorry, I meant to say it doesn't come on...

And @ diesel911, thanks for the info about the alt cables! I'll test those as soon as I get off all my weekend activities such as baby showers and the like

...

tangofox007 · #11 09-04-2010, 02:31 PM

Quote:

Originally Posted by Diesel911

Off subject but when I removed my Alternator to change the Bearings it had a Rebuilt by Bosch North America sticker on it.

As best that I can tell, Bosch offers (or did offer) two grades of rebuilt alternators. The "premium" version (aka "Professional Preferred") is alleged to have better bearings, etc. A number of the no-name overhauls just regrease the original bearings. (Sometimes I think they just repaint the case and call it "overhauled.")

Quote:

Originally Posted by Diesel911

I was surprised to find that the Bad Bearings I removed from it were Made in China.

I was equally surprised to find factory-installed Chinese wheel bearings on my '82 300D. My alternator, though, had FAG bearings, made in Germany. I replaced them recently with the same.

Quote:

Originally Posted by Diesel911

Since I got the new Bearings really cheap on Ebay I just replaced them with another set of Made in China Bearings.

Last time I checked, there were plenty of SKF and FAG bearings on Ebay, also. Sounds like you missed a great opportunity for an upgrade.

There is absolutely no reason to go to the dealer for alternator bearings. Or any other bearing that I can think of.

cirrusman · #12 09-06-2010, 03:06 PM

So I finally got to test the alternator; it's still not charging after I cleaned all the connectors coming from the alternator and the connections in the little black box showing in the following picture:

Cleaned them all with a wire brush. I tested the connectors by bridging each screw from the box to the negative battery post, and the tester light went on with all screws except for the one marked with a red arrow. The one marked with a blue arrow is the one going to the alt light I think, and it made the light go gon in the tester too. What is the red one for? How can I further test what's going on with my alternator?

JamesDean · #13 09-06-2010, 03:48 PM

If I'm not mistaken the red is either the wire to the starter or the wire from the alternator.
Its either the green or the red marked wires that go to the starter or alternator I can't remember which.

When you say its not charging, do you mean its not outputting any voltage to the battery?

TESTING ALTERNATOR DIODES:
Put a DMM across the battery, in AC mode, you should see less than maybe .5volts (i forget the number, but it should be very small) If you see more than this than one of your diodes is bad in the alternator and its not rectifying the ac wave fully. Solution: replace alternator. If you're going to replace the alternator I'd recommend the AL129X upgrade as seen here ("Alternator" 115 Amp Bosch AL129X works in 123s!)

You might also want to check ground connections from the battery and engine...

cirrusman · #14 09-06-2010, 04:05 PM

Quote:

Originally Posted by JamesDean

When you say its not charging, do you mean its not outputting any voltage to the battery?

I don't know if it's not outputting any voltage to the battery at all, I'd have to go to checkers to have them check it I guess, but with the engine in idle I can tell that the electrical stuff like windows, wipers and such are drawing power from the already discharged battery and not from the alternator as they work very slowly. I followed the 2 green bolts and they go to the battery, so I guess the red would go to the starter... With the battery plugged, the 2 green screws light up the tester light, the blue and the red don't; with the battery disconnected all of them light the tester light; can't really make anything of this except maybe a bad ground somewhere? I'm not all that good with electrical stuff. The alternator light in the dashboard works fine (the bulb that is) but still does not comes on when I turn the key...

JamesDean · #15 09-06-2010, 04:11 PM

You should pick yourself up a cheap multimeter...it'll help loads in accurately diagnosing your problem. You need to assess:

1) battery voltage -engine off
2) battery voltage -engine on @ idle, after a quick rev)
3) battery voltage -under load (headlamps,blower)
4) battery voltage -at 2000rpm or so under no load
5) battery voltage -at 2000rpm or so under load (headlamps,blower)

A cheap meter like this one will help
http://www.oreillyauto.com/site/c/detail/WMR0/W2974.oap?keyword=multimeters+%26+analyzers

It very well might be your regulator, I just replaced mine in my SD 1/2010..and its not output much voltage. The alternator itself i believe is OK. I'm going to order a replacement and we'll see.