The small copper contacts in the front wheels - Page 2 - PeachParts Mercedes-Benz Forum

barry123400 · #16 11-16-2010, 11:57 PM

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.

Alastair · #17 11-17-2010, 06:03 AM

Yup, Static discharge 'brushes' Static can build up when using brakes, causing crackling on AM radios....

Also, they form the 'earth-return' for the low brake-pad wear indicators...

But, Here's an interesting question. The earth return from rotating hub is transmitted to the stub-axle by the brush, which transfers to both top and bottom suspension arms via the ball-joints...

But HOW does the earth return from bottom and top arms--Via RUBBER bushes.....???
--There's no extra path like an earth wire Ive ever seen on any M.B Ive owned, so How is there a connection across the rubber bushes...?

--Is it 'connected' via the steering components...?

layback40 · #18 11-17-2010, 06:10 AM

You are right Alastair. Its via the steering components. They are all slow moving metal to metal rubbing surfaces with a degree of interference in their fit so good electrical connection. in theory wheel bearings have clearance.

Stretch · #19 11-17-2010, 06:12 AM

Quote:

Originally Posted by Alastair

Yup, Static discharge 'brushes' Static can build up when using brakes, causing crackling on AM radios....

...
--There's no extra path like an earth wire Ive ever seen on any M.B Ive owned, so How is there a connection across the rubber bushes...?

--Is it 'connected' via the steering components...?

It probably goes through that bulkhead ball joint - what's it called again? It connects on the LCA just under the spring on a W123 and is the main for adjustment of castor - come on help me out here!

Anyway part number for the little springs is:- 201 547 00 85 just in case you want to know.

layback40 · #20 11-17-2010, 07:30 AM

Army,
isint that rod mounted to the LCA through a pair of rubber bushes with a bolt through the middle?

Stretch · #21 11-17-2010, 07:45 AM

Quote:

Originally Posted by layback40

Army,
isint that rod mounted to the LCA through a pair of rubber bushes with a bolt through the middle?

Doh - yes you're correct - I thought of that whilst I was on the bog...

There is a vague possibility that they add graphite to the bushings like they do for aircraft tyres but I think that is highly unlikely. If I ever get really bored I'll make a continuity check - but at the moment life is too short.

triacon · #22 11-17-2010, 08:08 AM

Lets try this again...

If I start the car and turn on the lights, open the hood and disconnect the battery and the lights stay on, the alternator is working.

If I was then able to sever the alternator belts while the car was running, would the lights stay on?

If the lights went out at this point and I reconnected a good battery, I think the lights would go back on and stay lit until the battery wore out...

I am asking questions, I am not about to try this. Just want to understand what the battery and alternator do, and if there is some other part in the system that would allow the lights to stay lit if the battery were dead/disconected and likewise with the alternator....

layback40 · #23 11-17-2010, 08:16 AM

I think you have the idea right, dont try the disconnect though with the motor running.
A simple sign of a alt working is to have the lights on with the car idling. When you rev it up the lights will go a little brighter. That is a sign of a alt working. If the lights just continue to get dimmer with the motor running above 1500rpm, you have a charging/alt problem. I once had a problem with the thick wires from the alt to the cars elec system.
If the idiot light isnt working when you turn the ignition on before starting, the alt normally wont start to charge. It needs the current through the light to start the alt working.

scottmcphee · #24 11-17-2010, 11:19 AM

Think of it this way:

Everything runs off the battery. The alternator charges the battery.

If you have a dead battery it doesn't hold charge, but allows charge being put into it by the alternator to go straight through to the devices using power. This is fine so long as the engine is running. However it's tough on the alternator to feed a draining battery plus all accessories all the time. This can lead to a dead alternator.

If you have just a dead alternator then everything runs off the battery until it is depleted. As in you're driving home at night and the headlights get dimmer and dimmer and dimmer... until dark. You will know a dead alternator soon because you will kill the battery in short journey using power accessories at night.

But as you've discovered in this thread, the diesel engine will not stop for lack of battery, or alternator, once it is spinning. You can (and must) stop the engine by starving fuel. Vacuum is used to starve fuel when you turn the key off. There is a vacuum circuit through the key cylinder, running in parallel with an electrical circuit going through the key cylinder. This remote stop feature does exactly the same thing as you would do by pressing the STOP level on the IP under the hood.

Once stopped, you will not start with dead battery. Getting a boost can get your car running. Or, you can also push start the car, even though it is an automatic (sometimes a little known fact about MB's). Now it's running again in the dead battery condition (above) and no power accessories will work.

It's not fair to say "your car works fine without a battery", but it is fair to say "your engine will run without a battery". You'll agree driving at night in a rainstorm is impossible without good voltage in the car.

triacon · #25 11-17-2010, 11:52 AM

That's exactly what I thought Scott,

Thanks for the details.

Just to change things a little...

So, if you can get your car started (but it has a dead battery) you should disconect the dead battery in order for the alternator not to be working too hard, running electrical items AND trying to charge a dead battery...

This will keep your alternator from being stressed, but you should really be driving in daylight, with no rain and the radio off. Climate control off as well........ So as to not harm your alternator......

barry123400 · #26 11-17-2010, 12:34 PM

Temporarily back to the grounding issue. Normal brake fluid may or may not be conductive. I suspect not but do not know. Once becoming contaminated with moisture and residual junk it may be at least somewhat conductive. That might be an additional ground path for the semi isolated front.

Also to take into consideration is that with the brushes at the hub active both the hub and spindal are held at the same potential so there would be no arcing between them.

triacon · #27 11-17-2010, 06:19 PM

Spoke to a mechanic about the dash light for battery that is not lighting. He suggested to do the following. Take a test light and connect it to the blue wire off the alternator. I did this and turned the key. The test light glowed, so did the glow plug light. Started the car and the test light stayed on. Tried to call the mechanic with the results, but he had already left the shop...

So, what does that tell anyone with experience? Is my bulb out in the dash (that dipicts the battery), that activates charging of the battery...

scottmcphee · #28 11-17-2010, 07:02 PM

Quote:

Originally Posted by triacon

So, if you can get your car started (but it has a dead battery) you should disconect the dead battery in order for the alternator not to be working too hard, running electrical items AND trying to charge a dead battery...

Not quite, if you have a dead battery, you should drive to the store and buy a new battery. Stop the car and disconnect both (+) and (-) wires, remove the old battery and put in the new one and reconnect wires.

Tip: Disconnect (-) first for removal, but connect (+) first for installation. This way, if your wrench touches surrounding body metal while tightening the (+) terminal you get no sparks.

I know this has nothing to do with copper tabs in the wheel. Yell OT or go with the organic flow, your choice.

triacon · #29 11-17-2010, 09:51 PM

Quote:

Originally Posted by triacon

Spoke to a mechanic about the dash light for battery that is not lighting. He suggested to do the following. Take a test light and connect it to the blue wire off the alternator. I did this and turned the key. The test light glowed, so did the glow plug light. Started the car and the test light stayed on. Tried to call the mechanic with the results, but he had already left the shop...

So, what does that tell anyone with experience? Is my bulb out in the dash (that dipicts the battery), that activates charging of the battery...

After dinner...
Checked battery in the car with the car not running. Meter read 12.02 v. Started the car and still got 12.01 v. turned car off, hooked up test light, started car, still got 12.01 v. I was expecting the volts to go up thinking that the test light took over where the dash light (battery, or charge) failed to light... revved the engine, a little, but no change in volt reading...

babymog · #30 11-17-2010, 10:12 PM

First, 12v with the engine idling is not good, indicates that the alternator is not working.

The lack of battery light in the dash tells me that either the light is burned out, which will cause the alternator to not charge, or the alternator is bad (or brushes or volt regulator). Have the alternator tested or check/replace the bulb, the instrument cluster simply pulls out.

DO NOT DISCONNECT THE BATTERY CABLES ON A RUNNING ENGINE! The alternator's voltage regulator relies on a load to buffer the alternator output, and you can damage/destroy the voltage regulator by running an alternator charging system with the battery disconnected. The alternator is fine charging a dead battery, but not without a battery.