In August I acquired a beautiful 77 240D after much research and looking. Mechanically, the car is in great shape, the engine has 189k miles on it, and for the most part, everything is original.

A month after driving the car, the battery quit on me one Sunday afternoon while out running errands. This is my first diesel, and my first car in over 10 years, so I was interested to learn about the strong amperage a diesel starter pulls each time you start it, and how you need to drive around at least 15-20min or so to regain that lost charge. News to me, but ok. Jonathan at Midwest Performance Cars here in Chicago gave my car a once over head to toe, and reported no issues with the electrical system or alternator. We swapped in a new, larger, battery and I was on my way. He also recommended that if I plan to continue short tripping the car, I should look into investing into a battery maintainer, which I did.

Given that I live in the city, and I don't use the car for work, the majority of my trips are indeed short. So I got a Schumacher maintainer that uses a low 3V trickle charge to keep the battery at 100%. After using that and monitoring my charge for a month or so, I began to feel as though this were merely a stopgap fix and not really solving the problem, which was my that my battery never seemed to regain it's full charge (even after semi-long and longer trips). In fact it was always slowly losing its charge, which caused me a lot of anxiety.

After a little research I came across an electrical repair tech page. I landed on the infamous alternator regulator page, and decided before I invest in a new alternator, I may as well swap this part out and see if that doesn't fix it. This page from Diesel Giant also boosted my confidence in thinking this may be problem. So after reading through those, I bought the new regulator from Mercedes Source and followed their instructions on replacing the part.

Last Saturday I crawled underneath my 240D and used a right-angle screwdriver to remove the old regulator. My hunch was that this part was the original from 1977, and once I removed it and saw how worn down the contacts were, I felt like I was right. I installed the new regulator, with long shiny contacts and took the car out for a few errands, stopping and restarting the engine at least three times while I was out. When I got back home, I checked my battery level using my maintainer, and noticed it had actually gained a charge for once. I plan to buy a multimeter to keep a close eye on the battery levels in the future, but for now, it seems like this quick fix did the trick.

Anyhow, just thought I would share my experience, as I read this site alot now. I'll post photos later tonight of the old voltage regulator, to show how worn the contacts were.

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Eric, nice looking 240D and one of my favorite colors. Welcome to the Forum.

That was an easy fix once you figured out what it was. The ground strap from the engine to body can be a source of problems sometimes. Gave me fits for a while till I removed it and cleaned the contact areas where it bolts down.

That is low mileage for year, it may not be correct if the spedo gear has slipped in the past which is common to these 123`s.
We are up to 372K on our 240D and runs like a top, so you have some catching up to do.

The M source link will be blocked by this site.

Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

I,also, had to replace the regulator brushes in the 180,000 plus range The dash light started to come on slightly at times.

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Paul 1987 300 SDL; 2000 ML; '69 MGB; '68 VW Fastback

you don't need a multimeter if this is your one question - consider hardwiring a small voltmeter directly from the battery harness to the chassis so that you can always see the present voltage (when the car is off).

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'77 240D, 504H, OM617.952, etc.

I considered this or an ammeter but figured that once the system is working, it doesn't give much trouble and I have more important projects for the car. Also, gauge space is tight and boost and egt will be more important when gauges rise to the top of the list.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

I forgot to mention, I also replaced all my fuses with a new set from M. Source as well. Wasn't sure this was needed, but I thought for the $7 cost of the new set, it was well worth a short. And now I have many extra fuses on hand as well, should I ever need them.

Drove the car around last night again for the second time since installing new Voltage Regulator, checked the battery level before I left, it was at 12.9, and once again when I got home, it was at 14.1, so I think it's safe to assume the battery is now charging as it should.

Also noticed for the first time since owning the car, the interior instrument panel lights are all bright and functional, and the headlights are now MUCH brighter than before. Have yet to test the radio, or power sunroof, but looking forward to that.