Alternator Upgrade - PeachParts Mercedes-Benz Forum

JohnM. · #1 06-11-2010, 12:59 PM

Found a clean 120amp alternator from a 1994 S320. It had the M104 24V engine so I think this should drop right in to my 300E?

MTI · #2 06-11-2010, 01:07 PM

Yes, it should fit. M102/M103 owners have also been able to retrofit the 140A Bosch alternators from the V-8 S Class as well.

JohnM. · #3 06-21-2010, 12:03 AM

About 3 miles from home today all of my electrical stuff started failing. ABS light first, SRS light, then stereo, turn signals. Thankfully I was able to make it home, but the Optima battery was dead once I parked the car.

First checked the voltage regulator and it was toasted. One carbon pad had completely fallen out and one was really worn. I replaced this Bosch unit only 2 years ago (50,000mi)! But I guess they are a wear item. I have one on overnight order from Fastlane for $40.

Hopefully that's the problem.

I was looking at the alternator I pulled from the S-class. It has 3 plugs on the back and no visible regulator to remove? My stock alternator has 2 plugs, which look like the exact same as the 2 on the S-class (one small ring terminal, one large power). The S-class seems to have a 3rd spade connection on it? How would this wire in to my 300E?

compress ignite · #4 06-21-2010, 02:09 AM

JM,

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

Excellent tutorial(With High Quality Pictures) on Bosch 120 Amp Alternator
Self Reman.
(Yes it's from a VW...But Bosch is Bosch...)
The Rectifier is different,which makes the Output Terminals different.
your Voltage Regulator is in-cased in the Rear Black Plastic Cover.

This is BA's reman of a 143/150 amp V12 Type alternator:

http://v12uberalles.com/Alternator_Bearing.htm

[In Diesel Land ,We usually ignore that third spade type connector,It's for
the Tachometer and Mercedes Diesels use another source.]

samiam44 · #5 06-21-2010, 12:50 PM

I've rebuilt my 143A. Let see I think the 110A-143A are the same frame size. The 150A is a little bigger- but all will fit. Big advantage is these put out a higher voltage- around 14 volts instead of 13.5 or so of the older ones. Headlights will be noticeably brighter.

You may need to clock the alternator rear body to match the orginal configuration. I had to do this- not hard. The regulator/brush pac is about $25-35 depending on where you buy a bosch one. Reliability is iffy on non-bosch ones. IF you spin it and it feels rough- brgs. The front brg may or may not be easy. Rear is really easy and cheap (6303 brg). You can get the higher grade synthetic grease, electric motor grade for $5-10 unless you want american and then figure $20.
The wires- you'll need to upgrade and make a new harness. The original 10 gauge wire just won't carry the current. The activation lead is needed- which is a switched source. It should be a round termial which goes on the stud- ? 4 or 5mm nut holds it to the alternator.
DaveM has some pics on his website. He made a harness for his 1987 300D. So you'll need something similar, but lengths may need to be different.

Michael

JohnM. · #6 06-21-2010, 06:11 PM

compress, yes, that is the same exact alternator I pulled from the s320. Thanks for the link. I will look for a picture of the harness mentioned as well. I am wanting to do this upgrade soon, but not now.

Hopefully the regulator coming tomorrow will get me back on the road. I went out this afternoon and it seems my Optima has recovered a little bit. Looks like I will have enough juice to crank it up after replacing the regulator! Nice. I was going to have to call MBZ roadside assistance for a jump otherwise.

Kudos again to FastLane. $40 including overnight shipping for a replacement regulator. Can't beat that!

JohnM. · #7 06-21-2010, 08:52 PM

2 year old regulator:

babymog · #8 06-21-2010, 10:36 PM

It's not the most robust design John. The alternator is IMO undersized, and has to work much harder than it should, doesn't put out enough at idle to keep the systems running.

My '91 died Christmas Eve, in a blizzard, on a freeway between small towns in Michigan. It had about 60,000miles on it, was over $75,000 with the luxury tax, and the $39 brush failure gave no dash light nor warning before systems started to fail and lights dim, ... and of course you can't turn off many of them. So my expensive car spent its evening being pushed off of the road by a $15,000 POS State Police car, ... that could charge its own battery.

Fortunately, an upgrade to the later-style Bosch with 120amp or more charging, gives the low-RPM output to not short-cycle batteries, and is well worth the swap. I wish I had known this when my '91 was new.

JohnM. · #9 06-22-2010, 11:01 PM

New regulator got here this morning. My Optima had recovered enough to start the car. Back on the road.

compress ignite · #10 06-26-2010, 12:43 AM

The Brushes "Push" against them to maintain electrical contact.
(Oichan' s Picture Below, "After" ["Shaving" he called it].)
('Second picture is the "Before".)

In your picture of your "Bad" Brushes,notice how one is Much More Worn than the other?
'Did you have a chance to inspect the Slip Rings on your Alternator for wear,
when you replaced the Regulator?

JohnM. · #11 06-26-2010, 01:56 PM

Quote:

Originally Posted by compress ignite

The Brushes "Push" against them to maintain electrical contact.
(Oichan' s Picture Below, "After" ["Shaving" he called it].)
('Second picture is the "Before".)

In your picture of your "Bad" Brushes,notice how one is Much More Worn than the other?
'Did you have a chance to inspect the Slip Rings on your Alternator for wear,
when you replaced the Regulator?

I was wondering about the seemingly uneven wear. The repair wasn't done at home, so I didn't have a chance to inspect the alternator much. I was thinking when that brush popped loose the tip of it got chipped/broken off. But it totally makes sense that this alternator might be on its last leg. I'm pretty sure it has a bad diode(?) as well, the lights dim a lot at redline.

I want to put this 120amp S-class alternator in ASAP. I just need to build the beefier harness and get a new belt on the way.