Traction PROBLEM WITH TRANSMISSION -TNF75A NEED EXPLANATION

[crb111]

Dear all, lately I was in my field with TNF75A.

All of a sudden the transmission lamp started flashing and the tractor shifted to high automatically and moved in forward only.

It seems that all of a sudden it went crazy.


Now I am in hold of a circuit diagram and I am checking the solenoid Valves one by one, and by powering the forward solenoid manually I managed to drive the tractor out of the field.

My question is regarding the combination of solenoid valves the tractor has as I do not know clearly their function.

It has two , which are labelled as forward and reverse which I assume are the forward and reverse driving solenoids.

Another is the dump solenoid which seems to dump all the hydraulic pressure to off load the pump ( actually I do not know its main purpose)

Another is the HI-LO solenoid which I think shifts from LOW to HIGH range and versa, although when I applied power on this solenoid when in forward I saw no difference in speed.

The last valve which is present and I have no idea at all of its operation is the shuttle mode solenoid valve . Can anybody explain what is the purpose of this solenoid please and at which instant it is suppose to operate please.

Thank you

 

[TractorTech]

Don't remember what solenoid it is you are referring to, but back up a little. The light 'flashing crazy' on the dash is actually giving a code as to what might be wrong and where to look. The light should flash rapidly, pause, flash a certain number of times, pause, then flash a certain number of times, giving you a code #. The code should be in your op. manual or call you New Holland dealer or respond back here to find out what it is trying to tell you.
Example: flash rapidly, pause, flash 3 times, pause, flash 2, repeat sequence. This would be a code #32.
You may have a short, a bad controller, a sticking valve, a bad solenoid, but you are basically guessing at this point.
Also, the dump solenoid is the solenoid that puts the shuttle system in neutral.

 

[crb111]

About two years I had replaced the ecu as it was gone, now it seems that the problem is striking again. I have no error code pattern as the light blinks intermittently, and without any pattern at all.

What I will be doing now is replacing the ecu by a PLC which I will program myself as I cannot afford to stay changing the ecu all the time.

At this stage I have operated the forward and reverse valves , and now even the dump.

Now I need to know what is the purpose of the shuttle mode solenoid and how should I operate the HIGH LO solenoid .

 

[RickB]

About two years I had replaced the ecu as it was gone, now it seems that the problem is striking again. I have no error code pattern as the light blinks intermittently, and without any pattern at all.

What I will be doing now is replacing the ecu by a PLC which I will program myself as I cannot afford to stay changing the ecu all the time.

At this stage I have operated the forward and reverse valves , and now even the dump.

Now I need to know what is the purpose of the shuttle mode solenoid and how should I operate the HIGH LO solenoid .

High, low & reverse are achieved via two clutch packs (A&B) and one synchronizer. The clutch packs selects high or low range, the synchronizer selects forward or reverse, but only by way of an engaged low range (B) clutch pack. Hence the lack of a high/low shift while in reverse. The A & B solenoid coils are PWM coils, so a steady diet of 12V will significantly shorten their lives, and not modulating the applied current will result in incredibly harsh engagement.

Edit: Absent some undetected additional problem, the odds of a second ECU replacement being necessary is low, IMHO. Many of these units failed, particularly just before and after the introduction of the "A" series, but replacement ECU's have been much more reliable. I'b be looking more at the shuttle solenoid and the shift rail position sensors and associated wiring.

 

[crb111]

Thanks for your assistance . Sincerely i did not really understand the combination of the solenoids.

Is there a combination chart available explaining how the valves should be operated? Pwm is not a problem as i can apply it.

My main concern is what combination of valves should i switch for forward / reverse and high/ low.


Your assisttance is much appreciated

 

[RickB]

The transmission section of the appropriate service manual should have what you need. Sections can be purchased separately.

 

[crb111]

The transmission section of the appropriate service manual should have what you need. Sections can be purchased separately.

Actually i have all the original service manuals bit i cant find anything similar.

Regarding the shuttle valve and hi lo solenoid what is their main job ?

Thank youv

 

[crb111]

Dear Rick , by any chance do you have the service manual page which indicates the transmission solenoid operation pattern please.

Thanks

Actually i have all the original service manuals bit i cant find anything similar.

Regarding the shuttle valve and hi lo solenoid what is their main job ?

Thank youv