Why won't my tractor start?

OK, so it’s a 1984 Kubota 3750 4WD diesel, not highway-ready (top speed is 14 MPH, and it’s pretty scary at that speed) - but otherwise it’s just another motor vehicle with a problem that’s driving me nuts:

When I try to start it, six times out of seven I can hear the starting solenoid go “clunk” but the starter never kicks in; except sometimes it starts cranking immediately, but most of the time if I turn the key several times in a row, at some point the starter will spin and the tractor will start up. (And sometimes - usually when I’m out in the back field - I can tun the key 20 times in a row with no luck; but if I wait 10 minutes and try again it it will usually start right up.)

I opened up the solenoid and found the contacts badly pitted, so I put in a new starter - no change.

If I put the battery charger on it for an hour, it would usually start up right away (but not always); if I didn’t charge it up then it would mostly go clunk. So I put in a new battery, checked all of the cables and put a new terminal on the main power cable (the old one was so deformed it couldn’t be tightened up) - no change.

I checked the alternator output, and it looks fine - getting close to 15V at the battery when the engine’s at working speed.

Could this be the ignition switch itself that’s bad? I can hear the solenoid kick in every time I turn the key, but maybe it’s just not pulling in all the way?

maybe your battery cables are in bad shape under the insulation?

Battery connections are the first place to begin when you have a “No Crank” situation. Even
if you have a new battery, if the connections are loose, dirty or corroded, you will not be
allowing the full flow of current to pass thru the connections. The connection may be
enough to turn on the lights, but not enough for the huge flow that is needed to operate the
starter. This is where many people say that they know the battery is good….”because the
lights come on”. This is no more a battery test than licking a 9volt battery. It only tells you that there is electricity…not how many volts or the amperage that flows from the battery.
Jump starting may have wiggled the terminal just enough to allow the current to pass and start the engine, but tomorrow you have the same problem.

First remove the cables from the battery and use a wire brush to remove any corrosion and dirt from the battery posts and the cable terminals. There is a tool with a round wire brush for this purpose, found at any auto parts store for less than $10 http://shop.advanceautoparts.com/p/kd-tools-terminal-battery-brush-kdt201/25980576-P?searchTerm=terminal+brush.
Before connecting the cables, apply a coating of di-electric grease to the battery posts this will keep oxygen away from the connection so that it will not corrode as fast.

It is just as important that the other end of the cables also have a clean connection. Remove the positive cable from the battery again so that you do not short anything out. Follow both cables to their far ends, remove this connection and wire brush the connection and the cable terminal clean and retighten these connections.

If there was work done recently, there may have been an “engine to body” ground that was not installed following the work. These grounds normally run from the rear of the engine to the firewall and are uninsulated and most are a braided wire. If any of these are found unattached…reattach them.
Remember….this is not a “Sherman Tank” don’t over tighten the connections.
Tight…tight………………too tight…broke!!!


I fixed a similar problem on a friend of mine’s tractor a couple of years ago. I simply trash canned his crappy starter solenoid and replaced it with a Ford external solenoid. They are the best ones out there and are built very rugged. Make sure to check every cable and connection though because your problem may not be the solenoid at all.

Remember how old it is too. So stuff like this is normal. In addition to the great suggestions here, when I have questions about mine, I get on a Kubota tractor forum. You wil get experienced fixes from a bunch who have had problems that are similar.

I’m not a tractor guy but could this problem be related to a compression release issue?
Maybe a mechanical cable/lever type or possibly related to engine valve lash?

I mention this because at one time I discovered that valve lash was the issue behind my lawn tractor not starting although granted it’s smaller and a gasoline engine.
The symptoms were that it would mimic a dead battery, bad starter motor, and/or seized engine that would clunk hard and not start. Snugged the valve lash up a few thousandths and hard starting problems went away.

The trouble you described sounds like it could be either bad solenoid contacts or a corrodid battery cable. You have eliminated those things though you didn’t say anything about the ground cable. Check the voltage getting to the starter motor and at the battery when things aren’t working. See what the diffrence is. Maybe the battery has an internal problem. If the compression is so strong that the motor isn’t rotating, as @ok4450 stated, and the battery is good the cables should get pretty hot rather quickly due to the current load. If they don’t then I would say either the ground wire has a problem or the battery has an issue.

If either the starter motor supply voltage (the thick wire) or the starter solenoid control voltage (the thin wire) is low, erratic operation like this can be the result. Both should be above 10.5 volts during attempted cranking. Measured directly at the starter motor, between the terminal and the starter case. That’s where I’d start.

Flex your Battery cables. If you feel wires breaking inside, replace the cables. If you feel wires breaking and cut the cable cover open you will find the wires mad brittle with green corrosion. I also agree wit all who said check for a bad ground.

Also, was your starter supposed to be shimmed? If it fits too close to the flywheel teeth it can bind.

Pull the starter and bench-test it or have it bench tested…What do the brushes and commutator on the armature look like? Maybe it’s time for a starter rebuild…

Glad to see you’re still around Caddyman. :slight_smile:

It’s always one problem or another but ground the engine to the body solidly and try again. Sometimes the problem never comes back. Look for the cable that should be doing that and clean the ends and reconnect. If there isn’t one, make one.

My thoughts were along the same lines as oldtimer’s.

If you’ve confirmed that you’re getting good voltage at the starter (NOT at the alternator… although that’s important too), than (since you’ve changed the starter assembly) the starter gear may be having difficulty engaging with the flywheel ring gear. You could have damage to the ring gear teeth (or starter teeth if it came sans the gear) or binding due to improper adjustment (shimming). Visually inspect the ring gear teeth and check the starter motor assembly adjustments. You might be able to find technical data on the tractor manufacturer’s website, or perhaps a dealer can provide that for you.