Hope those of you who have ever had issues with your differential lock pedal find this helpful.
I Spent Saturday disassembling my 455 because of a differential lock pedal which I would bump and accidentally engage and it was causing the rear differential lock to engage occasionally, even when I didn't want it to. After rebuilding my rear differential unit this summer with new seals, gaskets, etc. (no bearings or hard parts required) and reinstalling it in the tractor, I would encounter sporadic times when the rear differential pedal would be engaging the differential. So, not having time to bother with it during the mowing season, I simply unhooked the pedal rod from the pivot bracket mounted on the rear case by removing the spacer #16 and cotter pin #15 shown in the lower illustration. While this disabled the Differential Lock, during the summer I didn't miss it as I rarely use it.
I knew I would need to address this before winter but just kept putting it off because I knew this was going to be a small project. In order to get to this particular assembly, you must remove the tractor rear fender platform assembly with seat, remove the fuel tank and re position all of the fuel lines and rear wiring harness as well as removing the rock shaft cylinder, rear pivot assembly and some other components (rear weight brackets, etc) to really be able to get in between the inner frame rail and the drivers side of the rear differential.
I was concerned that perhaps I had bent either the bracket shown at the spacer numbered #16 in the lower illustration I have attached. On the upper illustration, the bracket is the one held on by bolt #12 and has a 90 degree bend. But once I got in there, another bracket, which pivots on a pin on top of the bracket held in by bolt #12 which serves as a rear and forward stop for the rod movement, which is part of the entire rear assembly looked like it was functioning normally. My tractor uses the solid, non adjustable rod shown as 13b below.
Most of the linkage components are tucked up inside of the C shaped frame rail on the drivers side of the tractor and difficult to see in it's entirety. For those of you who have worked on these tractors, you know precisely what I am talking about. Not wanting to drop the entire rear end assembly out of the tractor as I did when I rebuilt it, I did the best I could to see the various components in an area which is busy with lots of other lines, brackets, hydraulic hoses, driveshaft, brake components not to mention the drive pedal linkages, etc. on the opposite frame rail.
The spring shown in the lower illustration as #9 on the front pivot shaft is actually designed to create pressure on the pivot rod and it puts downward pressure on the pedal giving it a consistent feel when you push the Differential Lock Pedal instead of simply up and down. The pivot bushing shown as #10 and #11 in the lower illustration were both knocked out of position due to wearing their retaining lips off over time. I replaced both of those bushings, which restored some "smoothness" to the pedal but still appeared that it did nothing to resolve the issue. Once I had the long rod #13b removed, I checked it so see if it cleared all of the things which it runs through, over and around and the rod was not hanging up on any of the other parts nor were they any rub marks where it was making contact.
Turns out that when I reinstalled the entire rear differential assembly this summer, apparently the bracket shown in the upper illustration held on by bolt #12 and the flat "L" shaped bracket which pivots on the pin retained by washer #3 and spring clip #2 in the upper illustration had been slightly bent downward on the rear of the bracket (perhaps while jacking the complete rear axle and differential assembly in place). I removed the bracket and straightened it in a vice and reinstalled it (very limited work area between frame and rear assembly) but I couldn't tell if this would entirely resolve the front of the pivot bracket from engaging the shaft on the rear differential which causes the locking to occur.
I don't recall how much clearance there was before between the end of the pivot bracket and the shaft engaging mechanism in the rear assembly. It appears that the front of the pivot bracket actually rides on the end of the Differential locking shaft inside of the rear end making contact at all times, just not enough to engage the differential.
Not wanting to have to disassemble this again for this issue, Instead of a simple cotter pin or a spring clip, I installed a round spring loaded clip (like a small key chain ) through the end of the rod #13b and attached a pull spring which has a solid loop through the retaining round spring clip. This way, the new spring I added can't fall off the retaining clip and the long rod can't come unhooked. Then I made a 90 degree bracket which is mounted through one of the rear cover assembly bolts and created a spring pull on the activation rod #13b towards the rear of the tractor. This causes the differential pedal, #5 in the lower illustration, to fully return to it's maximum upright position through the pedal floor board.
The result is a much firmer and consistent Differential lock Pedal which cleanly engages and disengages as it should. Now the pedal has a nice feel when pushed and it releases to unlock the differential fully. I reassembled everything and tried the tractor in snow plowing situations and it worked great. Over the years, I have found it was easy to "bump" the differential locking pedal when just re-positioning my size 14 feet and occasionally engaging the differential lock even when I didn't intend to. Now the pedal has a nice firm push required and releases to a full upright position. The pedal is actually higher than it was by about 1" to 1.5" or more so "bumping it" when simply shifting my feet should be less of an issue.
It appears the problem is resolved and the pedal actually functions better than when new.
Looking at the lower illustration, I am wondering if John Deere actually accomplished the rear spring pressure with the revised rod with the clevis pin and internal spring, which they are showing in 13a on the lower linkage illustration. It appears that the later built tractors use the rear differential lock pedal rod with the clevis and internal spring, perhaps to achieve the same result as I did with the rear pulling spring, to provide that pressure which releases the rod fully. Otherwise, It's not clear why they would have used that style rod shown. Depending upon the tractors serial number either the differential rods shown in the lower illustration as 13a or 13b are used.