73 w115 w/ 300TD 617 Alternator problems - Mercedes-Benz Forum

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post #1 of 2 (permalink) Old 03-18-2013, 04:44 PM Thread Starter
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Post 73 w115 w/ 300TD 617 Alternator problems

Good Day everyone. I am sharing my experiences with everyone in hopes to help someone else that is in need of fixing and doesn't know were to start.

I have a 1973 w115 Euro model. a few years back I took my 617 TD from my 1984 benz that wrecked and rolled , and Installed in the w115 with factory manual tranny from the 220D, the Flywheel clutch from the 220D, and the rear diff and radiator from the w123.

Despite the car being a rocket ship to mars. It has ran great for years, 1 clutch change, and rear FLex Disc Change.

Lately I have had problems with my charging system. I was getting the indicator lamp on the dash at idle. Goes away at higher RPM, output 14-14.5V

Battery always 12.86 disconnected. Thinking it was the battery, or the Voltage Regulator. (Diode pack ordered just in case) I went for the regulator, $60 in my country. Seems the part number matched up with millions of other BOsch Alternators from VW's to some weird car I never heard of.

After replacement the light is brighter at idle but goes out at low engine revs. I can see the lights get a little brighter at night when revving around above 1200rpm. Same Voltage and reading across the board. And no GOOD charge of the battery.

After no luck with Volt Reg, I proceeded to remove the Alternator. Its the double pulley type. SO I assume its 65Amps being my old 1984 benz was powered everything.

Took apart the alternator and De-soldered the diode pack from the Stator coil (3x 14 gauge wires), and checked for ground shorts from each phase to the body of the stator coil . 2x of the phase windings were shorted dead. The rotor and slip rings and bearings were all still in good shape I cleaned and re-greased bearings anyway.

P.S. after checking old Voltage Reg and Old Diode pack, everything actually is/was working fine.

To further diagnose were is the short I grabbed AC line voltage and shorted one of the grounded windings to the body of the stator. It sparks at the point of grounding, proceeded to the next wire, same thing almost same location. Third wire, Nothing happened as expected.

After removing the windings in that area ( you can do this by cleaning out the paint in the middle of the cracks and pull each wire out towards the center of stator, and then out.) Basically you can remove windings in one area. So the issue it appears the lower end of the stator was rusty and the paint washed/vibrated away, and eventually caused the resin coating on the copper 14 ga wire to ground to the body.

Today I worked extensively with a fellow mate that rebuilds alternators and we are re-winding the entire stator coil. We have cleaned and sanded the body of the stator and dipped in paint and placed speacial paper spacers to prevent shorting again. Once we have done we will take pics and upload progress.

I am sure it will work fine and much better than ever. Fingers Crossed.

( I could not locate the Stator coil at Bosch or anyplace, even used . I think nobody knows that they are doing anymore. It seems like most parts places give up after the first 10 min of searching and move on to the next customer or try to sell the entire replacement part)

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post #2 of 2 (permalink) Old 03-27-2013, 07:10 AM
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Date registered: Sep 2012
Vehicle: 300sel W109, 280S 70 , 220s 62. 230 66. Lancia Flavia 63.Pininfarina
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Very informative .
Seems one bad diode or a phase winding can still extinguish the warning light yet not provide the required ampreage under load, best checked with amp meter .
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