I repaired my front end. 1985 300SD, needed brakes, saw other problems that led to replacing upper control arms, lower ball joints, calipers, bearings...

Had the car all back together and now noticed when I start it, the red light that usually pops on (to the left of the glow plug indicator) is not lit.

Last time this happened, I brought it into the shop that replaced my alternator and they said the replacement showed a bad diode...

So, I am wondering if those little copper contacts in the front axle stubs need to "contact" the hub cup. Or perhaps the wire used to plug the vehicle in for preheating the engine in really cold weather, perhaps its wire is exposed and touching metal....

I plan to start my car and take the negative cable off the battery to see if the vehicle keeps running or not. If it keeps running, I guess the indicator light is burnt out! If the engine stalls, then my alternator is bad again...

But the contacts in the front wheels, I would like to know if I needed to prep them by over bending the pre bend in the contact, forcing it to rub the inside of the cap....

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1985 300SD

If its not contacting the cap its not doing anything. Btw, these are anti static contacts for the radio. Grounds the car or something

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1981 300SD 512k OM603

so, is the angle preset and a good contact, or are you supposed to open them up more prior to putting the caps on?

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1985 300SD

They're springy, just bend the copper out so that you know placing the hub cover on it will make contact. You can also tell by looking at the inside of the hub and see near the center a cleaned / swept area where the contact is supposed to hit. If you have undisturbed grease it's not touching like it should.

If you're not a big AM radio listener then you'll probably not miss these little dealies if they're off the car completely.

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Cheers!
Scott McPhee

1987 300D

Not a good ideal to lift a battery cable off with car engine runing. Not many electronics to get damaged on your model but I would not do it. You will get away with it many times but the time will come when you do not.

These cars are pretty simple compared to more modern vehicles. Boosting vehicles also has a risk component as well if not careful and even then. A good samaritan act can backfire.

Just reading the battery voltage with the engine on and off will tell you if the alternator is charging. At no risk at all.

No voltmeter? Headlights slighty brighter with the engine running than not indicate in a crude fashion that the alternator has output.

well,I did take the cable off while running. The car kept running so I figure that the altenator is still functioning properly.

I did read the post reply before this one AFTER doing it and must say, I think I got lucky with the cable removal...

I will pull the front wheels and look at the grease etc... I will pull the copper contacts out a bit if the grease is loaded into the center of the cap.

At this point, I suppose that the indicator bulb is burned out for the battery...

Is it hard to get at? I would like to change some other bulbs in the dash. Can't see how much fuel I have when it's dark out...

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1985 300SD

Your car will stay running with no battery or alt. Not like the gas cars of the 70's.

To pull your instrument cluster, just get two coat hangers and bend a short hook on the end of each and push them in between the cluster and dash about an inch or so. rotate them until you feel the back of the cluster and pull forward. real easy You can replace all the bulbs and put it all back together in about 15-20 min or less. Your engine does not requier power to run just fuel and air.

Really not good with electrical trouble so, how do I check my altenator if I can't do it by pulling the negative cable off the engine? Should I use a volt meter as someone mentioned earlier? AND if those copper contacts were not touching, could that damage the altenator?

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1985 300SD

Check your alternator using a multimeter across the battery terminals.

With the engine running, meter DC volts, should be ~13+ VDC.

Switch the meter to AC volts and it should be <100mVAC

(A possible problem area is corrosion between the regulator and alternator housing.)

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Sam

84 300SD 350K+ miles ( Blue Belle )

There are many threads on here about testing your alt. Best you do a search.
The little copper things are there to provide a good earth for the brake ware indicator tabs.
I am surprised that some one was able to show you a bad diode from the alt. They are mounted on a plate & require replacing as a pack. how did they show that one was faulty?
Dont ever disconnect the battery with the motor running.

Good luck with your car.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Back in March 2010 I got tired of hearing a chirping and or squealing belt on my car. When the engine was cool, I inspected things and found that the alternator was loose at the bottom bolt.

There is a repair shop near my workplace. When I have problems that I can not fix myself, I bring my vehicles there. I asked them to check out the alternator because of what was mentioned above. I also kept hearing a rattle.

When they looked further into the situation, they found that the bottom bolt worn, as well as the bosses on the alternator and (I think) the engine were out of round. Things were loose for a while and rattling around. Some threaded rod and nuts, washers, lock washers and a rebuilt alternator were installed. The car ran fine with the rebuilt until late September or early October. That's when I noticed the battery indicator light not lighting when initially turning the ignition key...

I drove the car like that for a few days until one morning, everything was dim in the car on my way to work, the CD player was acting up, blower , finally the blinkers were inactive, wipers too, I pulled into the lot at the repair shop near work. They tested things out and told me the rebuilt alternator was bad. The diode was bad. Not sure how they knew it, but they got another rebuilt and put it in, the light that was not coming on (little red battery light) was now working, so were all the electrical items in the car...... Whatever machine they used to test the alternator in the first place was used to test it after the second rebuilt was put in and I was out of there, on my way home at the end of the day... Results from the test said all was well...

I guess they used a diode testing machine. What do I know. I am not fond of electrical problems and I guess it shows. Will bring it to the same shop tomorrow. I will ask them how they diagnosed the bad diode in early October and will let you know the answer...

What I don't understand is this... If a diesel engine is not affected by removing the negative cable on a good battery while the engine is running, BUT has a bad alternator, where would you get power to run the lights and wiper blades. In an earlier post here, I think someone is suggesting such a belief. Is there another power source? Did I misread or misunderstand the advice? Please explain further.

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1985 300SD

here's the quote I am having trouble understanding...

"Your car will stay running with no battery or alt. Not like the gas cars of the 70's."

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1985 300SD

You don't need a battery at all after the engine is running. On the way home from purchasing my car, the battery totally died. Raining; no wipers, no lights, no turn signals, etc. But engine ran fine. Got home, turned off engine, tested battery. Zero volts.

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Mike Frederick
1986 300SDL, 240K+ miles
1985 300D KaliKar, 270K+ miles

The high voltage static charges that can accumulate discharge through the bearings pitting them. So the brass wiper performing it's radio interference supression is required for this as well. Less noticeable now that fm radio is the primary use band perhaps.