McCormick MTX185 rapidly changing down gears on its own

[k8andsteve]

Hi,
I thought I had posted this previously, but cant seem to find it.

The transmission will rapidly change down through most (if not all) the gears to 5th. Its really dangerous when going along the road as it just about puts you through the window. Another issue (which I think is related) is sometimes the display on the transmission controller will rapidly flash back and forth between 5th and 6th.

I'm wondering if anyone else has had this issue and can help me to resolve it.
Not sure if it helps but mine is Cummins powered.

Many thanks.

 

[davidroberts30]

@McCman

 

[McCman]

Hi, I'm guessing this tractor is a 'speed sequencer' tractor without a gearstick.
It sounds like you might have a power or an earth problem. Check all the battery connections make sure they are all connected, clean and tight. Under the brake pedals in the cab is an earth point check that's tight and good, under the cab in the back r/h corner is another earth point, check that's all good and tight also check the round multiplug connectors there.
Check the wiring on the back of the alternator is good and also check the alternator is working correctly as it needs this to make the gears work. Check the power stud on the front of the cab firewall under the bonnet, be careful as that stud is permanently live.

 

[k8andsteve]

Hi, I'm guessing this tractor is a 'speed sequencer' tractor without a gearstick.
It sounds like you might have a power or an earth problem. Check all the battery connections make sure they are all connected, clean and tight. Under the brake pedals in the cab is an earth point check that's tight and good, under the cab in the back r/h corner is another earth point, check that's all good and tight also check the round multiplug connectors there.
Check the wiring on the back of the alternator is good and also check the alternator is working correctly as it needs this to make the gears work. Check the power stud on the front of the cab firewall under the bonnet, be careful as that stud is permanently live.

 

[k8andsteve]

Thanks for the great suggestions. It is a speed sequencer tractor. I'll check everything over the next few days and let you know how I got on.

 

[njneer]

Had a problem once with one of these tractors with strange gear shifting long time ago.
I think from memory on the back of the tractor on the transmission wiring loom at the back,of the cab is the Can Terminator.
It is a flat “ dummy” plug, looks like a blanking cap plugging a spare plug on the loom but it contains a resistor to “ terminate the can messages if it starts to fail the system gets blocked up with can traffic and gets itself confused.
We had two identical tractors working and we swapped the terminator over and the fault moved to the other machine confirming it was faulty.
You can test the resistor with a multimeter set to Ohms resistance and across the pins should measure 120 ohms .

 

[k8andsteve]

Had a problem once with one of these tractors with strange gear shifting long time ago.
I think from memory on the back of the tractor on the transmission wiring loom at the back,of the cab is the Can Terminator.
It is a flat “ dummy” plug, looks like a blanking cap plugging a spare plug on the loom but it contains a resistor to “ terminate the can messages if it starts to fail the system gets blocked up with can traffic and gets itself confused.
We had two identical tractors working and we swapped the terminator over and the fault moved to the other machine confirming it was faulty.
You can test the resistor with a multimeter set to Ohms resistance and across the pins should measure 120 ohms .

Thank you, will try this also.

 

[k8andsteve]

Had a problem once with one of these tractors with strange gear shifting long time ago.
I think from memory on the back of the tractor on the transmission wiring loom at the back,of the cab is the Can Terminator.
It is a flat “ dummy” plug, looks like a blanking cap plugging a spare plug on the loom but it contains a resistor to “ terminate the can messages if it starts to fail the system gets blocked up with can traffic and gets itself confused.
We had two identical tractors working and we swapped the terminator over and the fault moved to the other machine confirming it was faulty.
You can test the resistor with a multimeter set to Ohms resistance and across the pins should measure 120 ohms .

Hi,

The a resistor had corroded and one end had broken off. I've replaced it and it seems to be OK so far. Big thanks for your help!

 

[njneer]

Hi,

The a resistor had corroded and one end had broken off. I've replaced it and it seems to be OK so far. Big thanks for your help!

No,problem , happy to help.
its one of those problems can take an age to find and can spend a lot on expensive parts and not get anywhere , then to find it a very cheap part that’s at fault.
Good it seems to be oknow?