John Deere 425 Diff Lock

weathda · Aug 13, 2020

I hardly ever use the "get me unstuck" pedal, but for some reason it's locked engaged and it won't unlock. The pedal linkage will move. The little butter fly looking tab in the side of the transmission seems to move as it should, but both the wheels keep pulling. It's an all wheel steer model too. Not good on the universal joints when turning.

Thinking it's something internal. Anyone had this happen?

beenthere · Aug 13, 2020

I wouldn't continue running it that way.. to avoid damage which you suspect might happen.

Some good pics showing the "butterfly" looking tab you mention may help with suggestions.

Remove the left rear wheel where you can look to see if the linkage to the transaxle appears ok, and then rotate the axle hub back and forth to see if you can dislodge whatever is binding.. (keep the right wheel tight to the ground so when the diff lock is engaged the left axle will not turn).

weathda · Aug 14, 2020

Thanks. So the tab circled in red is what moves back and forth and there is no resistance when it moves. I'm thinking the last line of your troubleshooting guide is what is the problem. Maybe a the pin (#7) or cir-clips (#5) have broken?

weathda · Aug 16, 2020

Little more troubleshooting this weekend. I removed the pedal linkage at the transmission. I verified the rod (#4) shown in the picture above is in the disengage position - it's sticking out of the transmission case. I can use a big screw driver on item #1 and push the rod in to the engaged position. When I let up, the spring will push it back out with a bit of force. This leads me to rods and springs are functioning fine. But that must mean the fork is broken or sheared off. It probably engages when I get on an incline and the right side dips, the carrier #11 moves in and engages the diff lock. To test this theory, I jacked the right side of the mower up and using a hammer and a block of wood, I tapped on the trans case and then got both wheels up off the ground. I could then hold one of the wheels from moving while the other spun - it was disengaged. It's probably fixed until the mower tilts and the carrier moves back the right again.

I guess the fork is made of pot metal and probably broke? Kinda stinks.

weathda · Aug 20, 2020

Mystery solved. It was the brake adjustment.

I was fully intending to remove the transmission to peak inside. I started removing the brake linkage and that's when I could see the brake mechanism pushing on the diff lock rod. It's hard to see anything outside the frame. Everything is tucked inside. Actually the brake pedal wasn't fully releasing. It wasn't until I pulled up on the pedal to see how much travel was on the rod when I heard a bang like the linkage was binding on a spring. It let the rod out probably another 0.25" of travel. I adjusted the brake linkage and took it for a spin. Good to go.