Dear Ole Mechanic:
I have a Case 930 tractor with a 401 diesel engine. It is about a 1960 model, with a 12 volt system. The problem is the solenoid will not engage the bendix. It has two new 12-volt batteries in parallel. I started the tractor and drove it out of the shop. It sat for a couple of days and then when I turned the key, nothing happened. I removed the starter with the solenoid all in one unit and connected it directly to the battery. I get a spark and a hum when the wire touches the post, but no actuation. I bought a new coil for the solenoid, and it does the same thing. I have compressed the spring manually and touched the post, and it will hold the core in, but it will not actuate by itself. I know direct current systems do strange things, but this has me stumped.
Thanks, John with Case
I hate to start an answer letter like that but it is your name. Yes, electrical systems do some very strange things; although, sometimes a mechanical problem will make you think the electrical system is strange. I think your problem lies in one of two areas - - - well maybe three - - ah, one of several areas.
The least likely is that the old solenoid coil went bad and when you got a new one, it was the wrong one--a 24-volt coil. Yes, Case did have some of their diesel tractors that had a 24 volt starting system in about the 60‘s time frame. Your tractor does not show to be one of those; however, I have not been able to find any information that verifies that your tractor is a 12-volt system. Getting the wrong coil is very unlikely, but it is still a possibility.
The next somewhat unlikely problem is that the starter bendix or the linkage is binding. Without the solenoid spring, the bendix and linkage should almost be floppy-loose. I would think that you would have noticed a binding problem when you compressed the spring manually;although, any binding could have been missed due to the spring pressure.
Another binding problem could be that the starter armature bushings are worn, allowing the armature to hit the field coil poles. This could prevent the starter from turning and cause it to draw so much current that the solenoid will not stay pulled in. This usually causes the solenoid to chatter in and out; however, with two batteries in parallel, it may just hum. Again this is unlikely, but manually turning the starter should let you feel any dragging or binding.
OK, now that I have covered some of the unlikely possibilities, I will get to the most likely problem--a bad electrical connection. Any battery that can maintain 11-volts should pull in the solenoid unless the 11-volts is not getting to the starter. The big question is; Where is the bad connection? There are a lot of places to check. I have seen a battery-cable-to-battery-post connection look perfectly clean on the outside, but once it was taken apart, it was very clear that there was enough corrosion between the clamp and the post to cause a problem. Another often overlooked area is the ground connections, Yes, the battery connection needs to be checked but so does the connection between the cable and the frame or block of the tractor. Also overlooked is the grounding of the starter to the engine block, where the starter in mounted. You didn’t mention how you connected the starter to the battery when you tried the starter off of the tractor. If you used a jumper cable for the ground and had it hooked to the block or frame and then used the tractor battery for the test, you could still have a ground problem with the battery ground cable connections. Another thing that I have run into is a battery cable that was almost corroded clear through inside the insulation. The only clue was some slight swelling of the insulation and a warm spot when trying to engage the starter. There is one last place where there could be a bad connection and that is in the starter itself. You see, the ground for the starter solenoid is inside the starter. Usually the ground is attached to the starter electrical contact feed inside the solenoid. Should the armature stop with the brushes on an open commutator segment, the solenoid will not get a good ground and have the exact problem that you are encountering.
I hope that I have covered this so that you can locate and fix your problem. If not, then please contact me again through the paper at firstname.lastname@example.org and I will see if one of my tractor sources of information from the Hill Country Antique Tractor & Engine Club might make a house call.
Herr Professor Nuzanbolts