Stuck differential lock in engaged position

I've got a MF 20 industrial. The differential is in the locked position and it is a pain to turn without chewing up the truf and/or grinding the front wheels across the ground. But, changing the lever position doesn't seem to do anything--it's in the down position but moving up doesn't even feel like anything is moving internally. I read a number of posts referencing stripping the internal gear in the differential and how that is expensive and time-consuming, etc., but doesn't a stripped gear mean that the differential won't lock? Rather than staying locked? Please advise.

Hello, there were several types of differential lock pedal fitted to the agricultural spec 135 so presumably similar
ones were fitted to the industrial '20'. I believe that it is only the pedal that is different. The pedal is clamped
onto a shaft which in turn rotates a ramp internally and causes the dog clutch on the side of the differential to
engage when the pedal is pressed.
First of all make sure that the spindle inside the pedal clamp is turning with the pedal. If the spindle is seized in
the axle housing the pedal can turn on it and give the impression that everything is normal and that the problem is
internal. The spindle normally has knurling on it to form a better 'grip' with the pedal. If the spindle should be
seized in the axle housing it will require patience and a penetrant such as WD40 (on this side of the pond). If you
can get a little movement on the spindle then carry on working it gently and it should become looser. The only other
answer is to remove the axle housing. You may find that a pin has sheared but normally you will have intermittent
operation of the lock mechanism if this has happened. Let us know what you find.
DavidP, South Wales

If your machine is as per picture or similar........?

With tractor backing up....pry PIN .....with appropriate pry bar / pry tool...
Do NOT TURN PIN......

Bob...

Hi Bob, that looks like a 'wet' brake axle. To the best of my knowledge the 20 has drum brakes. I believe that bigger industrials had wet brakes.
DavidP

David you are correct, I have the drum brakes. I'll post a picture in a minute.
I have never tried to move the lever by hand--just push down with my foot--but I did yesterday and you actually can feel the shaft move. I.e., it is not seized up. There is no significant resistance however, and there is no apparent internal movement.

When engaging the differential lock should the tractor be completely still? Does it need to be clutched? Or should it be rolling? Just wondering b/c my truck has different requirements for whether I'm shifting into 4WD in the Hi or the Lo gear setting and figured this might be the same....

Pedal can be pushed while tractor is still or moving, but lock won't actually engage until one of the wheels starts to slip compared to the other. I believe the control should be activated in anticipation of the wheels starting to slip, so that it will lock with the slightest of differential movement between the wheels and not once one tire is spinning away (slipping) like mad and the other is stopped due to full traction. I think that's what it said in manual, though it's been decades. David will know for sure.

Here are some pics of where the differential lock is on mine. It's dirty AH, but there's a grease fitting on it and I'm pretty good about hitting those every few months. In the front to back pic, it looks like I may be missing a spring of some kind.

Hi, OK, the pedal has a split pin through it into the eye of which a sprong fits and is attached to the bracket above. The spring is there to dis-engage the diff lock. Grease nipples are not normally fitted here and rely on the occasional oiling. Have to be specific here: can you actually see the spindle turning when you move the pedal? If you are sure that the spindle is turning then either the pin or something more has broken such as the fork or dog clutch ring.
To engage the diff-lock it is not necessary for the tractor to be stationary of depress the clutch pedal. Gentle pressure should be applied to the pedal until it engages. If you wish to engage it and it will not go in, steer a little left and right until it engages. If it won't disengage do the same. The effect of this is that you change to rotational speed of one wheel briefly. This relieves the load on the dog clutch and allows the spring to do it's job. Do not try to engage it at higher speed or when turning on a hard surface.
DavidP

First, thanks for all your info.

Here's the update: no problem getting it to disengage. I guess since the spring was off, there was not enough upward pressure to actually get the pedal into the correct position. So I let the tractor roll just a bit and carefully put upward pressure on the lever and there was just a little further movement and the differential was unlocked.

I have included a couple of pics with the grunge rinsed off the old girl. What I thought was a grease fitting (oddly placed, lol) was actually the place the spring clips in. Ironically, I just cleaned off my trailer and believe I saw this spring not a week ago. I have tried to attach edited copies of the pics oriented the correct way, but can't seem to do it. So, sorry for that.

Hello, I'm not familiar with any differences between agricultural and industrial versions. I presume that the diff lever is foot operated rather than it being a hand operated lever. If it is a foot lever then why is it at such a high position? In your photos is the lever at the top or bottom of its travel? Whichever it is there is something very wrong. The likelihood is that the pedal has turned on the shaft or has it been slackened and turned? Correct adjustment is full engagement with the pedal one to one and a half inches off the footplate.
You can check the pedal operation by jacking the RH wheel clear of the ground. You can then turn the wheel and engage the pedal at the same time.
DavidP

The pedal is in the "unlocked" position in the pictures. It may not be adjusted properly on the shaft. I think it must have been loosened when I engaged the differential lock, months ago, and then when I tried to disengage, the pedal's position with respect to the shaft wouldn't allow it to move fully into the disengaged position. I would guess that's why the spring came off--in the position shown in the (clean) pics above, the distance between the two tabs the spring connects to is shorter than the length of the spring.

When it was in the "locked" position, the lever was down closer to the floor plate/foot rest as you suggested. I just need to loosen that split-nut and move the lever to where it is the length of the spring, then tighten. I would imagine that'd mean that it would always be under some tension when the differential lock is engaged.

Sound right?