Ford 675d Transmission Engagement Issue

I am trying to troubleshoot an intermittent transmission issue with my Ford New Holland 675d backhoe. It is a 4x4 unit. The backhoe engine runs well.... A few weeks ago, the transmission started to intermittently slip and or is failing to engage in reverse and sometimes in forward. Sometimes it doesn't do either, but I noticed it first in reverse backing up a hill. I have noticed the condition occurs when the tractor is both warm and cold conditions on level and angled surfaces. I have changed the transmission filter, checked the fluid (might be overfilled), I checked all the wiring. I checked for leaks in the transmission cooler, I metered the transmission control unit under the dash and that appears to be working or meets voltage requirement when placing it in and out of gear. I have been running it with a gauge on it and it doesn't appear to be anything abnormal with the transmission pressure. Does anyone have any ideas or have any more trouble shooting steps? I have patiently been going through the book and trying to trouble shoot the issue. Sometimes when driving the tractor forward or reverse it just fails to move. I have also noticed the issue when transitioning from forward to reverse? All I know is that it is not consistent.
Shuttle valve issue?
Switch issue?
Bypass issue?
Clog?
I created a video so you can see the issue. The transmission is slipping in reverse in the beginning of the video. The transmission reads at 150 psi at engine idle and it rises up to approximately 180 psi during rolling operation.
Thanks in advance for the comments or help.
I haven't tried to verify if the issue exists when the tractor is run in 4wd. I will try to verify that in the coming days.

Youtube video: https://youtu.be/wAYjFlWj70I

This post was edited by RandyFord on 09/15/2021 at 03:10 pm.

I have a 455D with the same setup. I had
an issue where sometimes when the shuttle
lever was moved to reverse nothing would
happen. If you moved back to neutral then
back to reverse it would engage. The
lever assembly was kind of loose on the
steering column so I tightened it up and
it's been working fine ever since. That
shuttle switch assembly takes a lot of
back and forth, I would make sure that
it's working properly and not getting
flakey. Of course this may be too
simplistic. ... I've looked at the
troubleshooting section, lots of
possibilities.

Thanks for the reply Andy. I will pull that column switch connector off tomorrow and meter as I cycle fwd,n,R....I have been studying the maintenance and repair manual. There are a lot of voltage checks to do to try to pinpoint the trouble area. The intermittent function makes me think it is electrical in nature. I don't have a ton of experience with these tractors but one thing I have noticed when I check the transmission fluid is a lot of bubbles or cavitation/air immersed oil on the transmission dipstick when I check it during operation. makes me think a bypass valve or check valve could also be an issue. I don't know if it is normal to have some air in the fluid. I will try to get a picture and post it up here.

I appreciate the input and you sharing your experience with me as I try to sort this thing out.

This post was edited by RandyFord on 09/15/2021 at 07:11 pm.

I made some big progress today. I think I have it figured out. Before I started the tractor up today I performed the following measurements with my meter per the manual.

1. metered the battery voltage (12.5v), Not Running
2. metered the black input connector brown wire to ground to verify power on the command module under the dash (12.5 volts) Not Running
3. I metered test pin on back side of command module to ground (shuttle switch position Neutral 2.25v) (Forward 6.55v) (Reverse 6.55v). Not Running
4. I measured green and brown wire at the gray output connector. (0 volts Neutral, 12 volts fwd, 0 volts reverse)Not Running
5. I then started the tractor and tested the battery voltage again (14.1 volts)Running
6. I performed the torque converter stall test per the manual in 4th gear and it passed at 2000rpm.

***Here is where it gets interesting*** I drove the tractor and around my driveway. I went 100 ft and it stopped going forward like it slipped out of gear. I shifted it to neutral and to reverse and it wouldn't reverse either. I pulled up on the parking brake to set it for a test and it immediately jumped into gear.
7. I input the meter onto the back of the command module to see if it was recognizing the shuttle switch and measuring the correct voltage. It was (2.25 in neutral, 6.55v fwd, 6.55v rev).
I held the parking brake up slightly and I was able to back the tractor up. , Running
8. I placed my meter into gray connector output pins brown and green wire. The output 0 volts neutral, 11.15 volts fwd AND 11.5 volts when shifted to reverse. TADA. The tractor would go reverse with the shuttle shift in the forward position. I have a video of it and also the fwd and reverse

I believe that I have a faulty command module and it is outputting voltage to both legs of the shuttle shift valve sometimes and not outputting any voltage at others. I think I have performed enough trouble shooting to go ahead and replace the command module. All through the operation the transmission maintained 150 or greater psi. I also performed all trouble shooting in 4x4 and didn't observe any change from 2x4 operation.

I pulled out the fluid dipstick to measure fluid level during opeation and observed cavitation in the fluid.


@Andy Wickiser, if you pull your transmission dip stick out after some operation does it look similar?

Just curious. I think I am going to go ahead and order the command module and hope it remedies my issue.

Does anyone else see a different issue or something I am missing?

Thanks again.
RadyFord

I ran my backhoe around then put it away
and looked at the transmission dipstick.
It looked like oil fresh out of the
bottle.

Good work on checking the signals. I hope
that's the problem, too bad you don't have
a known good unit to sub in for
troubleshooting.