How to fix Kubota tractors that make clicking buzzing grinding noise when starting.

dixiedrifter · Oct 14, 2014

Ok so my M9000 has been making these loud clicking grinding buzzing noises when I go to start it. Finally think I have figured it out the problem... it is a small diode enclosed in a yellow rubber boot behind the alternator. There is also another one up front that I have yet to get to but from what I understand those go bad too. In my case my diode was completely open and blown, meaning current could not flow in either direction. If it was shorted (meaning current could flow both ways that would explain the clicking noise).

Upon dissection/inspection of the diode inside the boot it would appear that the diode is either a 3, 4, or 5 amp glass passivated sinterglass diode, possibly avalanche rated (but shows regular diode on outside of boot) Mine was completely cracked so there was no way to pull any numbers off it to determine the reverse blocking voltage or rated amperage. Definitely not a Vishay as the color is red.

If I had the parts numbers off of it I could cross reference an equivalent diode from alldatasheet dot com and probably get one off ebay for a couple bucks then make a new boot out of some silicone. Worst case scenario measure the resistance of the fuel shutoff solenoid (which I believe is the actual part making the noise) then figure out the amperage rating per ohms law and go from there. Then the only question would remain is how much reverse blocking voltage I would need to block whatever inductive kickback is generated from the solenoid.

Any pictures/numbers on a "shucked" diode would greatly help. Will try and post some pictures of the parts and where they are located tomorrow.

brain55 · Oct 14, 2014

Diode

I wish they had a picture of this.

Kubota parts diagram

This may help a little.

Brian

dixiedrifter · Oct 15, 2014

Pictures as promised. The first one is a picture of a diode part number 36330-75390 with the rubber boot cut away showing the internal diode. Very simple, just a standard PCB through hole mount diode connected to a couple terminal spades in a plastic housing.

The second picture is the location behind the alternator where the diode can be found. On my tractor look for the blue electrical tape.

My particular tractor has three of these diodes scattered about. The second one is located behind the battery up front.

This is the thing that makes the actual noise from what understand... the fuel stop solenoid. It is the "domey" looking thing on top of the fuel injector pump with the electrical connector in back, air bleed hose on the right side, and the two allen head bolts going thru the flange into the injector pump. When this thing goes down, you will not be able to crank your tractor. Mine is kaput, possibly from too many years of running without a diode and making all that racket or possibly the coil blew due to inductive kickback. Kubota wants like $200 for this part, you can get an aftermarket for like $100 or so. Simplest fix is to take the moving shaft that goes down into the injector pump and put it on a bench grinder and just grind it off. Then you can start your tractor normally, but you have to use the little red emergency shutoff knob in the cab to shut your tractor off.

Anyways as soon as I get around to tearing into it (not needed for operation, just normal starting) I will post some pictures of how to test these components along with relays and a few other things with a cheap $5 Harbor Freight multimeter.

rbargeron · Oct 16, 2014

So what purpose do these diodes serve and when did they become a routine feature?

In the old days big fuses were installed to protect against reversed polarity (like when jumper cables are connected backward). Do diodes help do something like that?