E300D ALTERNATOR ?? - PeachParts Mercedes-Benz Forum

rodm · #1 04-08-2015, 09:50 PM

My 1997 E300D while driving today had a battery charging light display on the instrument panel. My daughter was driving the car and kept driving for another 10 miles to the grocery store. After shopping the car would not start. I was able to jump start it easily. A voltmeter with the vehicle running shows 10.7 volts at the battery box in the in the engine compartment. The serpentine belt is tight and the pulleys are all snug. Can I assume the 90 amp Bosch alternator which is what is in the car.

Thanks Rodm

VW1300 · #2 04-08-2015, 10:32 PM

Could be the voltage regulator. This is an easy replacement, it unscrews off the back of the alternator. I did mine by laying under the car, 10 minute job and not expensive. Check to confirm what kind of alternator you have though, different kinds may use different regulators. I happened to have the Bosch.

What I don't know is how to diagnose a bad regulator - but it worked for me when my charging system was weak.

tjts1 · #3 04-08-2015, 10:42 PM

Yes something is probably wrong with your alternator. Could be bad ground, corroded terminals bad voltage regulator, failed diodes or something else internal.

The 90a alternator died on my 97 E300D last month. I didn't have time to take it apart and figure out what was wrong with it so I just replaced it with the 70a alternator that I pulled from my old 92 190e 2.6 before sending it to the junkyard 3 years ago. It bolted right in and I was back on the road in under an hour and the car seems perfectly happy with the 70a alternator. At some point I'll get around to diagnosing and maybe fixing.
http://i.imgur.com/zWLCXdu.jpg

Any MB alter alternator from mid 80s to mid 00s will bolt right in. 70a, 90a, 115a, 143a, and 150a are the most common ones. even some Bosch non MB alternator will bolt in from other Euro cars.

Zulfiqar · #4 04-09-2015, 11:04 AM

make sure your main battery wire is in good condition, There is a junction point where it splits from the starter to the alternator.

Once you are sure its good - then replace the alternator, most probably its a Bosch and the regulator is an easy swap, If its a valeo item its more pricey.

But you can use any older alternator like mentioned above.

Jeremy5848 · #5 04-09-2015, 11:40 AM

My 1996 and your 1997 E300Ds should be very similar ("identical?") in this area. If so, I can tell you that regulator replacement is easy with Bosch alternators, a little harder on Valeo. For Bosch:
1. Disconnect the battery, raise front of car, remove belly pans. (Theoretically possible to operate from topside but I've never tried.)
2. Remove the wires on the back of the alternator.
3. The Bosch alternator has a black plastic cover held on by 3 screws and may also have 3 plastic clips that are part of the cover. Remove the screws, lever the clips away from the alternator, pull the cover off.
4. The regulator (looks like a power transistor) has the brushes as part of it. (One of the most common failure modes is that the brushes have worn down.) Remove the 2 screws holding the regulator and carefully remove the regulator. The brushes may have worn "tracks" or grooves into the slip rings; if not too deep it's OK to just live with that.
5. Install a new regulator and put everything back together.

Although it's possible to install new brushes on the old regulator, it's probably not worth the bother—regulators aren't that expensive, only $34.50 from Pelican for gen-u-wine Bosch. I advise anyone with a regulator of unknown age to carry a spare. Even better, install the new one and carry the (if it's good) old one as a spare. That way you learn to do the job without being under pressure and lying in a snowbank; if the new regulator is DOA you can put the old one back; you have a known good regulator as your spare. Win-win-win.

Mind the other posters' comments about the problem possibly being elsewhere in the electrical system. It's not always the regulator!

Finally, as previously mentioned, any W124/210 alternator should fit. I replaced the stock 90A Bosch in my '96 with a 140A unit and the '95 E300D has a 150A. The greater charging ability really helps the battery quickly recover after cranking the engine and also helps in slow-speed driving if lots of accessories are running.

Jeremy

compu_85 · #6 04-09-2015, 11:58 AM

Does the 90A alternator get a clutched pulley?

-J

pimpernell · #7 04-09-2015, 01:04 PM

Quote:

Originally Posted by compu_85

Does the 90A alternator get a clutched pulley?

-J

Shop manual states that clutch pulleys were used. If that is not the original alternator, in may not have a clutch pulley. I know when I changed out my alternator, the new one came with a solid pulley, and when the engine was started it caused vibrations that were not there with the old alternator. Switched out the pulley, and all was back to normal.

Maxbumpo · #8 04-09-2015, 01:29 PM

Here's a great source for OE alternator and starter parts:

- Alternator & Starter Parts Wholesale

Jeremy5848 · #9 04-09-2015, 02:01 PM

I had to swap pulleys on both cars when I changed alternators. Don't remember either having a clutch.

TnBob · #10 04-09-2015, 02:29 PM

Both are good ebay items. Get them direct from Asia the way your parts store does.

Asia to my semi remote Tennessee door is usually 12 days.

Yes .. got mail all winter even during our nasty ice storm.

rodm · #11 04-09-2015, 02:40 PM

THANKS TO ALL. I will check the wires at the junction as someone mentioned. If that is good will try the REGULATOR if not new alternator. My alternator says on it BOSCH 90 AMP with a Mercedes logo.

Rodm

rodm · #12 04-10-2015, 01:22 PM

I charged the battery and the car started right up. Battery voltage was at 12.97 v. With engine running and everything OFF I tested voltage at the battery directly under the seat, it was 11.86 v. I turned the AC on high and immediately a squealing noise started from the front of the engine turning the AC on and off started and stopped the squealing. Would this mean not the VOLTAGE REGULATOR but, the ALTERNATOR. OR is there something else going on.???

Rodm

compu_85 · #13 04-10-2015, 01:26 PM

I'd say you need to look at your belt tensioner and belt to be sure they're working properly. A slipping belt will result in low voltage.

-J

rodm · #14 04-10-2015, 01:35 PM

With moderate force on the top belt between the pulleys I can get no more than a 1/2" of play. I have a new spring on the tensioner.

Rodm

Zulfiqar · #15 04-10-2015, 03:19 PM

Quote:

Originally Posted by rodm

I charged the battery and the car started right up. Battery voltage was at 12.97 v. With engine running and everything OFF I tested voltage at the battery directly under the seat, it was 11.86 v. I turned the AC on high and immediately a squealing noise started from the front of the engine turning the AC on and off started and stopped the squealing. Would this mean not the VOLTAGE REGULATOR but, the ALTERNATOR. OR is there something else going on.???

Rodm

If you are seeing anything less than 14V on a started engine, the alternator is not doing its job. If you got a heavy squealing sound on electric load then it also means the alternator is trying to charge but its failing to.

If your belt tension is OK and your alternator is not drenched in oil (too much oil in it can kill it) then best start checking the main wire to the starter/alternator and then also test the grounding wire under the car.