85 300SD alternator 65A or 55A - PeachParts Mercedes-Benz Forum

rsmartin · #1 03-02-2008, 06:02 PM

according to my Mercedes CD an 85 300SD has 65A alternator, so that's what I got at Advance which coincided with what they showed

Got the old one off.... the new one has a single pulley, mine has double pulley.

Old one has spacers to bolt a rear cover on with... new does not have the studs to receive the spacers

Old one has a spring clip to hold the connector, new one does not have holes for the spring clip

New one is slightly deeper than the old one

is this just a bad match? online vendors show 65A with spring clip and studs

my pulley has a slight dent in it so i was hoping for a new pulley

#2 03-02-2008, 07:08 PM

This is the correct 65A alternator:

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1CQ0J3JZ42BA14WJV7&year=1985&make=MB&model=300-SD-002&category=All&part=Alternator

I have a Denso in mine. Personally, I would avoid the McParts store rebuilds.

rsmartin · #3 03-02-2008, 09:59 PM

i returned the one from the store

after talking to my brother-in-law who is physics teacher, he thinks more likely my voltage regulator is bad based on description of my problem

my battery periodically becomes too weak to start car.... i've checked amps being drawn by placing multitester between neg battery terminal and negative cable... only drawing 0.02 amps so i don't have a current leak.

i drove 10 hours on Friday from Maryland at night with no problems maintaining lights, BUT within the first ten minutes of driving at night, all of a sudden my lights will brighten up...

so i went out just now to the car.... started it and checked voltage at cig lighter. with lights on it started out at 12 v then dropped to 10.5 at which time everything brightened up and i had 12.8 volts.

so, does it sound like voltage regulator to everyone else??

hey_allen · #4 03-03-2008, 01:06 AM

The voltage regulator is a definite possibility, and also relatively cheap and easy to replace on these alternators. (and if it doesn't fix the problem, yank the new regulator and save it for when it does fail, on a future alternator!)

On my car, I was having a somewhat similar experience, which would brighten at 3 minutes from the point I started my car. Clockwork, 3 minutes from the key turning on, each and every time.
I finally tracked my problem down to a glow plug relay sticking, and only shutting off at the 3 minute point.
Once I had found that was the problem, I disassembled the relay and discovered that the points on it's power relay were badly pitted. A little quality time with a points file and I've had no problems since.

You may not be having the same problem, but it's just one more possibility.

Best of luck, and please let us know what turns up!

LUVMBDiesels · #5 03-03-2008, 08:19 AM

If you do have to replace the alternator, do a search here for AL129X. That is a 115amp alternator originally found in Saabs. it is a bolt in replacement for the stock 65amp alternator with these changes...

1) remove the pulley from your original alternator and swap it onto the AL129X

2) You will have to rewire the connections from the junction box on the right fender to the alternator. This is very easy to do. just run a heavy gauge wire (10ga) from the large bolt onthe back of the alternator to the terminal that the pair of original wires connect to. Then run a small gauge wire from the small bolt on the back of the alternator to the teminal where the small blue wire connects.

This takes about five minutes to do and is a great upgrade.