TL90DT 4WD will not engage

bwvfan · Jun 16, 2014

I recently took my TL90DT out to do some brush work and noticed that the 4WD indicator light on the dash did not come on when I put the tractor in 4WD via the dashboard switch. I believe the tractor is either staying in 4WD or 2WD, and to me it feels like the tractor is staying in 2WD (if I do a tight circle on a hard surface and turn the 4WD switch on and off I do not fee the front axle engaging).

I have done the following to trouble shoot the issue thus far:
1. Checked the 4WD fuses - fuses OK
2. Checked the 4WD relays - relays OK
3. Checked the dash bulb - bulb OK.
4. Checked and cleaned the terminals on the 4WD pressure switch - no change in 4WD after cleaning (if I jumper across the two leads to the pressure switch the 4WD dash light will come on).

Any ideas on what I might troubleshoot or try next?

Is it worthwhile to remove and clean the 4WD solenoid?

I know that the braking system is tied into the 4WD engagement so that one has additional braking control via the front axle being engaged. Should I troubleshoot the 4WD pressure switch and 4WD solenoid before looking into any braking system related issues?

Thanks for your time and help - Bob

RickB · Jun 16, 2014

Remember the MFD clutch is spring applied and hydraulically DISENGAGED. Pressure switch controls the dash lamp, nothing more. pressure switch failures are fairly common, but only affect the indicator. A faulty BRAKE pressure sensor could be contributing ( there are two).

bwvfan · Jun 18, 2014

Thanks RickB - that makes sense.

I spent yesterday afternoon removing the 4WD solenoid (boy is that in a tight spot to get at). The solenoid looked good but I cleaned it anyway. I checked the coil pack to make sure it did not have an open circuit, and it did not. I then bench tested the solenoid and I was easily able to get the valve stem to move back and forth by apply and then removing power. So I put the solenoid back into the tractor. I started the tractor and tested the 4WD switch. I could hear the solenoid kick-in, but still not indicator light (which would indicate the pressure switch). I then turned off the 4WD switch and then applied the brakes and again could hear the solenoid kick-in, and again no indicator light. I alternated between the 4WD switch and the brakes, about 20-25 times, and then I could no longer hear the solenoid kicking in and out. So I pulled the solenoid again, cleaned it, bench tested it (and it worked), and then re-installed. I followed the same test loop and again after about 20 tries the solenoid stopped working again.

Maybe the solenoid is bad or sticking. With the MFD clutch being spring applied this would mean that most failure issues with the 4WD system would engage the 4WD system. My tractor still feels like it is not in 4WD. If I remove all power to the 4WD solenoid then by design the 4WD should be engaged, if it is not engaged then that should indicate the solenoid is stuck. Does that sound right?

Your input on the brake pressure switches is excellent, thanks. I don't have a TL90 wiring diagram so I am not able to follow the 4WD wiring circuit. Could a bad brake pressure sensor cause the 4WD not to engage? Is there a way I can take the pressure switches out of the loop to then see if the remaining 4WD is working? Would it be safe to jumper across both sets of the brake pressure leads to isolate them from the remaining system?

Again thanks for your help. - Bob

RickB · Jun 18, 2014

bwvfan said:
Thanks RickB - that makes sense.

I spent yesterday afternoon removing the 4WD solenoid (boy is that in a tight spot to get at). The solenoid looked good but I cleaned it anyway. I checked the coil pack to make sure it did not have an open circuit, and it did not. I then bench tested the solenoid and I was easily able to get the valve stem to move back and forth by apply and then removing power. So I put the solenoid back into the tractor. I started the tractor and tested the 4WD switch. I could hear the solenoid kick-in, but still not indicator light (which would indicate the pressure switch). I then turned off the 4WD switch and then applied the brakes and again could hear the solenoid kick-in, and again no indicator light. I alternated between the 4WD switch and the brakes, about 20-25 times, and then I could no longer hear the solenoid kicking in and out. So I pulled the solenoid again, cleaned it, bench tested it (and it worked), and then re-installed. I followed the same test loop and again after about 20 tries the solenoid stopped working again.

Maybe the solenoid is bad or sticking. With the MFD clutch being spring applied this would mean that most failure issues with the 4WD system would engage the 4WD system. My tractor still feels like it is not in 4WD. If I remove all power to the 4WD solenoid then by design the 4WD should be engaged, if it is not engaged then that should indicate the solenoid is stuck. Does that sound right?

Your input on the brake pressure switches is excellent, thanks. I don't have a TL90 wiring diagram so I am not able to follow the 4WD wiring circuit. Could a bad brake pressure sensor cause the 4WD not to engage? Is there a way I can take the pressure switches out of the loop to then see if the remaining 4WD is working? Would it be safe to jumper across both sets of the brake pressure leads to isolate them from the remaining system?

Again thanks for your help. - Bob

Having no 4WD in the absence of power to the solenoid could be a solenoid sticking open (fairly probably if your report of troubleshooting is entirely accurate) or a mechanical failure of the clutch (which would be likely NOT to come & go but be constant).
I'm only guessing, but I'd bet the brake pressure switches are normally open, so unplugging both should allow the 4WD logic to operate unimpeded by false brake signals. Alternatively, you could ohm the switches to see if one has failed closed, or the brake system is holding residual pressure.

bwvfan · Jun 18, 2014

Thanks again RickB

I had to go after work and get some additional hydraulic fluid so I did not get a chance to work on the tractor this evening. Back at it again tomorrow and will update with what I find. - Bob

Kevc · Jun 19, 2014

Have seen the couplers on the 4wd shaft slip back due to poorly seated clip on these tractors, would explain permanent 2wd!

bwvfan · Jun 20, 2014

Thanks Kevc - I will check the couplers.

mackone · Sep 1, 2022

Hi I know this is a old post, but I'm having the same problem with a TL 80 New Holland. When I looked under the tractor it looked like there is two solonoids one on top and one directly below it, which one does the engage/disengage of the four wheel drive or is it both? Thanks

Harry in Ky · Sep 1, 2022

What exactly about your tractor is "the same problem"?

As for solenoids, there could any number of them depending on what options your tractor or transmission came with.

Does this look familiar?

https://www.mycnhistore.com/us/en/newhollandag/tractors/agricultural/naba01agr049tl/tractor/front-axle-steering/idler-controls-4wd-pipes-solenoid-valves/cn/099516C5-B8BF-E111-9FCE-005056875BD6/8E0FAD4F-E6BE-E111-9FCE-005056875BD6