Mercedes-Benz Forum banner

Alternator or voltage regulator

1056 Views 32 Replies 7 Participants Last post by  vwnate1
Hi all

Hope you’re all well, w123 200 m115 engine (petrol) manual.

Went for a drive and indicators stoped working lights dim. When I parked up battery light came on and it was dead. Battery was old so put in brand new one (voltage was over 12.6) started up straight away but then the battery light was on constantly.

I checked the voltage and when engine running was giving me over 13.7v, I changed the voltage regulator (from original Bosch 0192052008) to a hella replacement one. Once fitted started all ok but battery readout varies at 12.15v when the car is running even with heater on full and lights on. Battery light is still on in dash though.

So is it a case of dodgy voltage regulator or alternator? Should I check the earth? Also a little bit of oil leak from before and it’s been pretty cold wet in the uk.

Any ideas or steps to check?

Thanks
Land vehicle Vehicle Speedometer Motor vehicle Odometer
  • Helpful
Reactions: vwnate1
21 - 33 of 33 Posts

· Registered
European 1974 350SLC ,'78 300CD& '80 300CD sold , '81 240D SWMBO's Car '84 300CD & Euro
Joined
·
969 Posts
I see you didn't bother to clean the copper slip rings in the alternator and this can prevent charging .

To clean slack or remove the drive belt and use metal polish and a clean rag, turn the armature as you get golden color on the slip rings ..Another thing is : it's very easy to install the voltage regulator so the brushes are not sitting squarely on the slip rings .

HELLA is just as good as BOSCH , beware of any other brands, many are made in Germany but never quite reach 14 VDC .

If the bent is slipping it's east to tell by trying ti turn the alternator by the fan blades behind the pulley ~ if it turns with no sound it's slipping .

It you can force it to turn with a squeaking sound the belt isn't tight enough .

If you decide to replace it, ONLY a BOSCH branded & labeled rebuild will do ~ other companies fail to properly varnish the armature windings to they often fail .

The 65 ampere W123 alternator is only on the 1985 year models in the U.S.A. , again, BE WARY of whom you buy from .

Most breakers will have at least one 65 ampere W123 alternator, the BOSCH part number is : AL117X and it will ave that number on a sticker on the side of the alternator if it's a proper BOSCH rebuild .

Most places will sell you a generic one that look the same but at most is 55 amperes .
 

· Registered
1979 w123 200 m115 petrol manual
Joined
·
14 Posts
Discussion Starter · #23 ·
Thanks for the apologies for not being able to update weather here has prevented any. Will get on cleaning it, hopefully weather will be better tomorrow for it.

yep Bosch is the way to go, will do all of the above and update.

thanks everyone for the help and input
 

· Registered
European 1974 350SLC ,'78 300CD& '80 300CD sold , '81 240D SWMBO's Car '84 300CD & Euro
Joined
·
969 Posts
No worries, no hurries .

When you're trying to remove the alternator be aware some of the 17MM ATF nuts on the face of the alternator are in fact WELDED IN PLACE and you'll need to undo the 1's from behind ~ seems really tough until you've done it a few times .

I highly recommend cleaning this area before you begin as these cars leak oil and have myriad nooks and crannie where dirt, oil and grease pack in .

There are cylindrical spacers between the sheet metal adjuster and alternator too, don't let them fall and roll away .
 

· Registered
1979 w123 200 m115 petrol manual
Joined
·
14 Posts
Discussion Starter · #25 ·
Cool mate, I checked the tension on the belt spot on 30 freezing here so only managed to do that will do the cleaning and diode/amp etc checks in next few days
Thanks everyone for the help
 

· Registered
1979 w123 200 m115 petrol manual
Joined
·
14 Posts
Discussion Starter · #26 ·
Hope everyone is well ok sun out in London still freezing but did something

cleaned the slip rings, re tightened double checked the voltage regulator, cleaned all the contacts.

voltage on battery was around 12.4 starting load it stayed around 12.2

(Voltage ripple test) was 0.01/0.02


with fan on full, hazards, lights full and beam voltage was around 11.4
(Voltage ripple test) 0.02/0.04

when engine turned off after battery voltage was back on 12.4

I can’t find the refurb Bosch alternator here in the Uk anywhere.
 

· Registered
European 1974 350SLC ,'78 300CD& '80 300CD sold , '81 240D SWMBO's Car '84 300CD & Euro
Joined
·
969 Posts
Okay ;

Here's where it gets interesting -

Now I feel badly for tossing out all those good used 55 and 80 ampere alternators...

You don't have any parthaus' there ? seems kind of odd to me .

I buy parts in the U.K. and have them shipped to the U.S.A. on a regular basis.......
 

· Super Moderator
1986/1990 W126
Joined
·
21,634 Posts
No, we don't have the same type of sellers. We have motor factors which are our equivalent, but so much stuff is not available through them because of the low numbers they'd be selling I guess.
 

· Registered
European 1974 350SLC ,'78 300CD& '80 300CD sold , '81 240D SWMBO's Car '84 300CD & Euro
Joined
·
969 Posts

· Registered
European 1974 350SLC ,'78 300CD& '80 300CD sold , '81 240D SWMBO's Car '84 300CD & Euro
Joined
·
969 Posts
First thing is to check the valve gaps, they're almost certainly too close or zero lash .

After that we'll cover diagnosing a miss .
 
21 - 33 of 33 Posts
Top