Alternator 4850

J. Schwiebert · Aug 28, 2016

My boy said I should check out the alternator on his 4850. The tractor is not here and if I remember right it is a different brand than what is on the 40 series tractors that are in there "fleet" So what brand alternator is it and are there disassembly and trouble shooting instructions as well as a parts break-down on the next? Thanks in advance. J.

Ragnarok · Aug 28, 2016

Most likely a JD 4850 will have a 'John Deere'(Nippon Denso) alternator....wires-up the same as a standard Delco with a two field wire plug-in connector and a single heavy wire.

The ND/JD alternators used on the 50 series are pretty decent. If the wiring is ok usually the brushes are worn-out(have to solder in the new ones)

Some of the JD tractors have a small diode harness in the wire harness(right side in front of cab purple wires)...if the diode harness goes bad there won't be power to one of the alt. field wires. Can't remember if a 4850 has the diode harness though??

Bob · Aug 28, 2016

The wire from the firewall over the engine to the #1 terminal of the alternator is a solid single-strand nichrome resistance wire and occasionally they break.

Deere offers a kit to bypass it with a new wire and diode inside a convoluted "loom".

Bottom line is that #2 should have battery voltage to it at all times and #1 gets fed from the key switch through the "idiot light", and resistance wire or diode, and "excites" the alternator at startup.

Key "ON", engine NOT running, ground #1 terminal, and the indicator light in the instrument panel should come on. If bulb is bad or there's an open circuit, likely alternator will not "excite" at startup.

matthies · Aug 28, 2016

If it is a Nipp. like stated, there is a hole on the back like a delco to full field the alt to bypass the regulator, it could also be the purple wire also. When we had problems with them at the dealership we would ask how many hours the tractor had, 2500 meant brushes and 5000 brushes again and bearings. You drill a hole in the end of the rear bearing housing then thread a small grease zerk in there and pump grease in there to push the end housing off of the bearings. The regulator is under the cover that is held on by two screws.

Alternator 4850

J. Schwiebert

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Ragnarok

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Bob

Well-known Member

matthies

Well-known Member

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