1240 Starter Help

[fuchifarm]

The battery cable going to the starter on my Mf 1240 keeps vibrating loose (terminal 1). When this happens the tractor won't start but I can hear it click like its trying to start. Today I went to tighten up the nut after this occurred and now the starter doesn't click like normal and the tractor won't start. The fuel pump still clicks on and glow plugs still work. I checked all the fuses etc and couldn't find any problems. I hooked a voltage meter up and when I try to start the tractor the voltage drops to 11.5V from 12.5V. Also the relay wire (terminal 2) coming from the safety relay only reads 7V . Normally there is a clicking sound from the starter when I turn the start switch. I thought maybe I had drained the battery but I jumped in a spare full charge battery with same result.

The lack of sounds mimics what happens when the tractor is in gear etc disabling the starter. However the voltage is 0 when one of the safety switches is engaged and not 7V.

I'm thinking something happened inside the starter. Maybe the magnetic switch for the plunger? The starter is a Nippon Denso. I plan to pull the starter tomorrow and bench test it. Is there anything I should try before pulling the starter? Attached is the parts diagram/ repair manual section for the starter.


Edit: Ok I just tried jumping the relay wire direct to the starter battery terminal and the starter turned over. So I guess its not the starter after all and must be something in the safety relay / engine stop relay.


View attachment parts starter.pdf
View attachment starter.pdf

 

[fuchifarm]

I was able to get it started by holding the start switch and jumping the relay line to the battery terminal. After stopping the tractor I was able to get it to make the normal attempts to start like the nut was loose again.

Its like the relay wire isn't delivering enough current to engage the starter cause jumping it the starter spins easily. I guess I'll be going through the harness looking for problems. I'll start with the starter switch (50) wire that goes to the safety relay and then fed to the relay terminal.



Here is the wiring diagram if anyone has a suggestion.
View attachment wiring schematic.PDF

Edit: After checking the relay and the starter switch and wiring harness I was able to determine they weren't the problem. I tried to hotwire the tractor again and the starter wouldn't turn over. Tapped it with a hammer and it turned over. Took the starter off and inspected the solenoid contacts and plunger. It was corroded and pitted. Trying to find a rebuild kit to replace the contacts and plunger. A buddy of mine has a friend with an alternator shop who rebuilds starters said he may have the parts so I'll be making a a trip to visit him tomorrow.

 

[fuchifarm]

Well I got the tractor running today. Took the starter over to buddies shop and got new contacts and plunger. Put it all back together and everything worked. Also discovered that the ignition switch terminal 50 (starter relay) was weak. I added in a relay between the switch and the safety relay using terminal 50 to activate the coil and terminal 30 to feed 12V to the relay. The starter spins like new every crank now.

Now I'm ordering 2 new brake boots cause when I stepped on the brakes the right side brake boot split behind the clamp over the brake rod. I may try to glue it together to get by for a week till I can get the replacement boots. Anyone have a suggestion on temp patching the boot?