Starter Solenoid - 400D

I have been having a problem with my solenoid chattering, or close to it. It is a fairly new solenoid and has never work right. I think both large posts should be isolated from the case, but the one I have is not.

I wired it with the battery negative on the top large post, and the starter to the bottom large post. The key switch goes to the small right post.

On the bench, with 12 volts between the bottom large post and small right post, it pulls in a bolt, which seems right. However, when checking with an ohmmeter, the bottom post shows about 1 ohm to ground. So, on the tractor, when the solenoid operates, doesn't the battery basically get shorted to ground? Shouldn't both large posts of the solenoid be isolated from ground?

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Ohmmeter readings for good solenoid should be as below -

At rest:
Heavy post to heavy post: (infinity)
Both heavy posts to ground: (infinity)
Small right post to ground: several ohms
Small left post to ground: (infinity)

Soleniod energized (12 volts applied to the small right post):
Heavy post to heavy post: 0
Both heavy posts to ground: (infinity)
...and 12 volts to ground should appear at the small left post.

I have found your diagrams EXTREMELY useful, and consider you the "master", but I gotta "call you out" on this one!

There is a "pull-in", and a "hold" winding in that solenoid, and the share a common connection point, the "S" terminal. The "hold" winding is internally connected to the solenoid's metal case, and the "pull-in" winding is connected to the "output to the starter" terminal.

He can leave one terminal of his ohmmeter on the "S" terminal, and then check the resistance to the case, and the large output stud. Each coil's resistance will be low, but if his meter is accurate enough, the coil between the "S" terminal and the solenoid's output stud will have the lower resistance of the two.

Here's a "quick and crude" diagram of the solenoid's internals:

Your diagram and description is right on - thanks for the correction!

Also, the newer one was noticeably smaller in size than the original one. Maybe it just doesn't have the fortitude to keep the plunger in. The newer one's plunger tube was shorter and the barrel was much smaller than the original.

I will see what the other one I ordered does for me when it gets here and let you all know.

Did the plunger come with the new one, or how are you matching the different sizes up?

Is the original Delco plate on the starter, with the Delco starter number?

What is the make and part # of the solenoid you have?

The solenoid is an Accurate 7951, made in Canada.

I don't know the starter number, but will look at it tomorrow. I am also going to recheck the wiring and connectors. Could be a problem there, but don't think so. Won't be back until tomorrow evening.

Thanks.

The reason for the two windings... one is terminated at case ground. This winding, alone doesn't produce enough magnetism to pull the plunger in by itself, but will hold the plunger in, once it's there. It's the "hold" winding.

The other winding draws more current, for more magnetic pull, but wastes power, and would heat up the solenoid in short order. So, for it's ground, they use the starter windings, which are so heavy, they "look" like a ground to the "pull in" coil. When the solenoid pulls in, and switches power to the starter, both ends of the "pull-in" coil are at battery potential, so it no longer is drawing current.

At that time, the other, grounded, "hold" winding is able to keep the solenoid engaged by itself.

If the solenoid or plunger you currently have are wrong or not matched to each other or the starter, the plunger will not seat all the way into the coil, and the "hold" winding, by itself, will not be able to hold the plunger in, and the solenoid will buzz or chatter.

That bottom big post is wired to the starter field coils and they don't show much resistance. Yes, it grounds the battery thru the field and that is what sets up the magnetic field to make the starter spin.

The winding of the solenoid uses two windings: a heavy "pull in" winding and a lighter "hold in" winding.

So, if the thing is setting there "chattering" against the spring and won't hold a load "in", it means that the hold in winding of the solenoid is bad.

I’d get a new solenoid and be done with it.

Allan

Allan