Best guess..

Is it possible one of the alternator bolts worked loose, or the bracket lower front ear fractured?


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If it were that wouldn't the belt be slipping?

Not always, if the ear fractured, it can cock at an angle pounding against the bracket.


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Well I'll have to check it out, I just hope the sound is related to something external and not something internal

84 Mercedes 300d Turbo Rattling Sound - YouTube

I looked close and I could see the cooling fan for the alternator moving out of place when the rattle would happen.

I'm relieved because I thought I messed the engine up running it low on oil, but I need to figure out why the alternator isn't charging.

I couldn't get an alternator reading from the Bennet Auto Supply near myself, but when I shut the car off the battery was at 12.39V and had 760cca, it read that the battery was @ 80% so it's good, just not getting charged.

The weather, though sunny in the video, has taken a dramatic change and is thunderstormin right now, gotta love the sunshine state with it's summer "monsoon season".

Hopefully tomorrow or Monday I'll be able to check it out, I'll have to just put the battery on the charger in the meantime.

I may take the cluster out tonight and take a look at it to see if it's preventing the battery from charging.

Hmm, maybe I didn't tighten the pulley bolt down when I switched them over. Try that first.

This noise wasnt their before the alternator change? The replacement alternator is a good used unit right. Im going to guess the noise is something in the alternator making the noise ,A washer or screw has found its way into the unit,If it sat around on a bench or a parts ben this could be a very possible scenerio .It also could be its bearing going out.You could take it up to a parts store to have it bench tested while also hearing for this noise to make itself known.If good but only noisey take it apart to see if something is in its cage. If not its likely a bearing issue

I can see the alternator fan moving out of place when I hear the noise, I'm going to check it out when I put the little one down for a nap. I also spun the fan while the engine was off and it would get stuck and have a lot of resistance about halfway through the turn.

Also, my gp light has been coming on at random, as well as when I get on the throttle, it's possible that I have a bad gp relay and that the alternator does in fact work, but the battery is being drained by the gp's coming on. However since my gauges are on the fritz that could also be preventing the battery from charging.

A bench test is in order, and there's a car quest about a block away from my apartment, I could take the alternator out and walk over there and have them test it. If it's good, and the voltage regulators good then that leaves my gp relay and the gauges. It's a pain in the ass but it is all pretty simple stuff.

Well I pulled out the alternator and there was no nut for the pulley, so that thing managed to unscrew itself and come off, although the pulley is still in tact, which explains the rattling. It tested fine, and I figured out the source of all my trouble (I hope), a loose ground strap, the chassis to bellhousing ground. I tightened that up, put the alternator back in and I'm in business, the car started right up with the starter, I just gotta get that nut but I'll do that in the morning, Lowes is w/in walking distance.

So I'll see if my gauges are good, the fuel gauge was close to E which may or may not be true, but my gp light came on as it was supposed to and turned off as it was supposed to; and my tach read what it was supposed to read.

Thanks Colin, and everyone else in the forum! You guys rock! And Colin, there is a good possibility that my old alternator and regulator still work so you may wanna check that out.

Yeah I think I put that pulley on and didn't tighten the nut down very hard because I wasn't planning on using that pulley, but didn't want to lose it. If you can't find it at Lowes feel free to swing by and I can give you the one off of your old one.

I'll test the alternator, but still at least we ruled that out completely.

Did this fix the starter issue too?

The starter is working now, so I guess it was just a bad ground that was causing the starter to work intermittently, and the alternator to not charge the car. I drove this evening and at startup everything worked as it was supposed to. Gp light turns on and stays lit for 10-15 secs, then the car started right up, but while driving I noticed the gp light came on why revved around 3k rpm and at the same time the tach started acting finicky. My fuel gauge may or may not be reading accurately but I have to wait til Tues before I can do a fill up. The needle is right above 1/4 tank, judging by what I've put it in that sounds about right. But while driving I had the fan going, the wipers, and the lights. 2 nights ago that was enough of a load to drain my battery completely, but I was able to make 4 short trips within a 2 hr time frame and when I got home there were no signs of a low battery,

I'm going to pull the cluster out tomorrow and clean all of the contacts and check the grounds, and add the extra ground like in the write up, hopefully this will solve the gauge issue, and maybe I can get my clock to work too. If that doesn't fix the gp issue then I'll switch the relay, and after that, I'm startin a new thread lol.

I think I'll swing by tomorrow to get that nut so that way I don't have to try to guess which size nut to buy. I'll shoot you a text and let you know what time.

I had a loose ground strap when I first got my first W123 Mercedes and it caused a lot of weird problems in the cluster lights in addition to not starting. As I recall, it damaged some traces in the cluster. Do a search with my screen name and stranded, there may be info in my thread that may help you.

ps, get the pulley too in case the pulley got damaged with no nut on it.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

http://www.peachparts.com/shopforum/diesel-discussion/277167-w123-300d-fuel-tank-sender-question.html

http://www.peachparts.com/shopforum/tech-help/190632-fuel-gauge-sending-unit-threads.html

http://www.peachparts.com/shopforum/diesel-discussion/71819-fuel-tank-light.html

http://www.peachparts.com/shopforum/diesel-discussion/189366-fuel-sender-85-300d-cleaned-pics.html


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