alternator brush wear
 

Does anyone know the typical life of alternator brushs in the 2005 CDI? I have 121k on mine and I've read that the life of the brushes is about 125K and should be replace at about that time- steve

It will vary, but today's MB alternators are made of kryptonite. I replaced the regulator/brush holder on my 300E at something over 250,000 miles. They are amazing. If it ain't broke don't fix it. When it stops charging, pull the regulator and check the brushes. It's a quick and inexpensive fix. The only other reason to pay any attention to the alternator is if it makes noise.

Hope this helps.

X2 with Larry,
Dont fix it if it isnt broke!!!

If it stops charging because of brush ware, normally the idiot light will not come on when you turn the ignition on.
As an emergency fix (works for a few k miles max.), if you are very careful, you can leaver the brush out a tiny bit with a couple of small screw drivers.They are formed around the wire & if you are ever so careful the brush will move out at tiny bit sliding on the wire. Twice I have done this (on different alts), its possible to gain 1/16" max. Just enough to get home or until the next day when the indi parts guy is open.
It would not hurt to have a spare pair of brushes ready, they are cheap. You need to be good at soldering to install them.

My 82 300CD had less than 162k on it when one of the brushes broke and the alternator stopped working.

Parents' 94 toyota previa with 230k still charges perfect... As did my 83 300D at 228k. And the parents' 96 E300D which has 210k.

These things seem to be all over the map...

What I recommend is to get a good baseline of alternator voltage, and then keep track (you can get a voltmeter that sticks into the cigarette lighter, for example), so you can see if there is degradation in time.

I like the dont fix if it ain't broke, except that Ive also had a diode go bad on me and discharge my battery as a result...

The way things are built these days (bottom cost, minimal quality even when you pay for quality) you could very easily swap out a 200K mile alternator that worked perfectly to "prevent" brush failure and install a brand new one that failed in 30K. Best to just let stuff last as long as it will, because Murphy's Law says that only those parts which were not preventatively replaced, should have been.

Consider buying a spare regulator to keep in the car. It's not expensive ($40-50) and small enough to hide in the spare tire well or glove box. If you are adventurous, go ahead and install the new regulator and keep the old one as a spare. That has the additional advantage of allowing you to learn how to R&R the regulator without being under pressure, doing the job on your schedule and in good weather and not while lying in the mud in the middle of nowhere with your family wondering where you are.