E39 528i alternator problem?

[kavery3]

Hey everybody,
I was driving my car around (528i/m52 engine) and several times the lights will dim and the radio will shut off. At idle when I rev it the cabin lights will get bright, then dim to almost nothing and the radio will shut off and sometimes the dashboard will light up for a sec. I figure the most likely suspect is the alternator. For reference when the car is running the multimeter shows the normal around 14 volts but when I rev it, it will drop down to 12 ish then back up again. Also, should be known that I'm running a 400w rms sound system. Is this my alternator going bad? Thank you so much.

[StRaNgEdAyS]

It sounds like your brushes are just about worn out.
If you have a Valeo it's pretty easy to replace just the brushes for $20. If you have a Bosch it's easier, but significantly more expensive, to replace the brush pack.

Sent from my G8141 using Tapatalk

[fullthrottle540]

Alternators generally operate in three phases of RPM. It could idle fine but lose power at mid or high rpm - signs of a bad alt.

[cnn]

Google Bosch AL0703N (not AL0703X), about $200.
Stay away from the junk at local auto parts stores.

[StephenVA]

+1 on reading your alternator brand first and the replacing it. As mentioned by other responders, your alternator is going dead at higher than idle. If you buy a $20 multi meter and set the unit to D.C. Voltage and place it on the jump points under the hood (best spot is the battery itself in the trunk) and read the voltage at three levels:
Engine off key in you pocket (this tells you a little about battery health)
Engine at idle
engine at 1500 and again at 2500
these last three quickie tests will tell you a little about the alternator output. As these things croak the voltage output will wonder all over as the brushes make and loose contact with the spinning shaft due to carbon build up. Yes, alternators can still put out the right voltage or even super high readings as they short out internally. That is why shops buy a large VAT tester as they will display voltage and Amp out put under a load test. If you turn on all your electrical items (high beams, radio, defrosters, etc) you can do a DIY load test in the driveway.

Battery health reading have been posted so many times I get tired of doing it. Bottom line over 12.5 volts? (50% charged)
Alternator health 14.1V min at all rpms

there are a few who choose to open the alternator and clean the shaft and replace the brushes then go on driving for many more miles with no issues. DIY skills good?
Only replace the alternator with the same brand and make sure it is new not a remain unit that has a 50% chance of working. That failed part will have you chasing your tail for a while.
search on this forum as this process is so overly documented it is ridiculous.
and please do not buy into a local parts guy telling you the brand does matter as the pulleys may not line up with your belts.

[kavery3]

Thank you for the replies everyone! This confirms my alternator is bad and will replace it with a new one before I drive back down to school.

[StephenVA]

Read your alternator back for details on brand and amp output

Your install is simple and easy. The fan/clutch needs to come out but you can do that with a simple 36mm open end long handle tool and a little WD-40 on the nut to break the seal of rust. Change out your two drive belts at the same time (Use Continental belts)

[adm750]

kavery3 and StephenVA -
I noted in a thread one time, that I have pulled the alternator out of the '97 528i twice now, cleaned the commutator and the brush pack, cleaned the trash out of the back of it and the cooling duct (I suspect a lot of these overheat and want to operate poorly due to blocked airflow to the windings from the buildup of road-shite inside that cooling duct...!!), re-assembled it, and it still keeps churning away.
I have almost 230K on that car and it is the original alternator.
Take a small pick and clean those groves where the brushes ride (to give it good gap) and put a nice sheen on the contact areas with a very fine crocus cloth. Hell - ya gotta take it out of the car anyways to swap the pulley, and trade the core, that's why I took a chance and tried to clean up the brushes and the contact areas first...

this is just me overspending my $.02 here...

[StephenVA]

Repost a few pic on this process for the all the newbies who are search challenged. (Why search when you can just ask and everyone does the work for you?)

[adm750]

Repost a few pic on this process for the all the newbies who are search challenged. (Why search when you can just ask and everyone does the work for you?)

if that was for me...I'll see if I took any.

I also took voltage drop readings across all cables to ensure I didn't have a resistance issue somewhere along the way too with these old cables.
That is something else that should always be done when working on issues such as these....the standard voltage drop test....which seems a lot of people forget the importance of

[StephenVA]

There you go again with the "testing first" not guessing approach.... That would only reduce this forum postings approx 80%. As everyone wants a solution to an unseen unknown/issue or symptom from someone far far away. Have to build a solution spinning wheel active image. Type in XXX get a solution. No guess work. Worth every penny paid.

Regarding the alternator lasting forever with a little rebuilding, you are spot on. My record is 250K with just new brushes, cleaning, and front & rear bushings.

Keep posting!