I'm rebuilding a diff for my '40... first timer. I have a new pinion and ring (Nitro) and ARB airlocker. I made up a set of setup shims and honed the outer bearing so it would slip on and off the pinion shaft easily. This makes the process go much more quickly than having to press or pound stuff in/out on/off between fittings.
Since I am replacing nearly everything inside the diff, including going to 3.73 from 4.11 gears, I didn't see much point in trying to use the previous shim setup as a starting point. So, to bracket it, we started with 0 shims and then went straight to 0.040". As we hoped, 0 shims was too shallow and 0.040" shims was too deep, so bracket achieved! We made three more iterations in our "binary search" for the proper fitting: 0.020" (too shallow, but close), 0.0215" (closer), and finally 0.023" which is where we stopped (patterns below).
The coast side looks primo to me (using ZUK's patterns as my main reference), but the drive side looks like it might be a hair deep. Also, I'd love some feedback on our process:
- Applied a thin coat of gear oil on (setup) bearings and assembled pinion into housing without any kind of sleeve.
- Applied just enough torque on the pinion nut to make the pinion stiff enough that it doesn't move when checking backlash, but easy to turn by hand. I figured that, as long as the inner race and shim(s) are firmly seated, the pinion nut doesn't need additional torque in order to get a valid, reproduceable pinion depth pattern... agree?
- Assembled the carrier and adjusted to the desired backlash. In my case, I'm shooting for the lower end of the spec range (0.006" - 0.007"). My reasoning here is that, since I will be taking my rig to the trail head on a flat bed, most of the miles will be slow, so the diff won't heat up as much as it would at higher speeds, say on the tarmac, so less backlash is better... agree?
- Measured the backlash, then tapped the carrier gently with a brass hammer and rotated the ring gear, and measured again on a different tooth. Up to this point, the cap bolts were only snugged enough to flatten the lock washers and the carrier adjustment rings have been adjusted with a spanner and punch and hammer (gently, by feel), so no measure of the carrier preload has been done. Again, my reasoning here is that carrier preload, as long as it is "snug", shouldn't affect pinion depth that much... agree?.
- At this point, we torqued the cap bolts to 50 lb-ft, rechecked the backlash (it didn't change at this stage on any of our iterations).
- Made sure the paint was spread thin and even (I ended up thinning it with some dub dee farty to make it spread better) and had my buddy put pressure on the ring gear while I turned the flange to get a pattern. One other note: I wiped all the paint off the pinion gear between iterations, which seemed to help with getting a clear pattern.
Below are the patterns I got, please let me know if you would run these, or suggest I try to optimize further:
Drive side:
![20220227_150626[1].jpg](data:image/svg+xml;charset=utf-8,%3Csvg xmlns%3D'http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg' width='1440' height='1920' viewBox%3D'0 0 1440 1920'%2F%3E "20220227_150626[1].jpg")
Coast Side:
Since I am replacing nearly everything inside the diff, including going to 3.73 from 4.11 gears, I didn't see much point in trying to use the previous shim setup as a starting point. So, to bracket it, we started with 0 shims and then went straight to 0.040". As we hoped, 0 shims was too shallow and 0.040" shims was too deep, so bracket achieved! We made three more iterations in our "binary search" for the proper fitting: 0.020" (too shallow, but close), 0.0215" (closer), and finally 0.023" which is where we stopped (patterns below).
The coast side looks primo to me (using ZUK's patterns as my main reference), but the drive side looks like it might be a hair deep. Also, I'd love some feedback on our process:
- Applied a thin coat of gear oil on (setup) bearings and assembled pinion into housing without any kind of sleeve.
- Applied just enough torque on the pinion nut to make the pinion stiff enough that it doesn't move when checking backlash, but easy to turn by hand. I figured that, as long as the inner race and shim(s) are firmly seated, the pinion nut doesn't need additional torque in order to get a valid, reproduceable pinion depth pattern... agree?
- Assembled the carrier and adjusted to the desired backlash. In my case, I'm shooting for the lower end of the spec range (0.006" - 0.007"). My reasoning here is that, since I will be taking my rig to the trail head on a flat bed, most of the miles will be slow, so the diff won't heat up as much as it would at higher speeds, say on the tarmac, so less backlash is better... agree?
- Measured the backlash, then tapped the carrier gently with a brass hammer and rotated the ring gear, and measured again on a different tooth. Up to this point, the cap bolts were only snugged enough to flatten the lock washers and the carrier adjustment rings have been adjusted with a spanner and punch and hammer (gently, by feel), so no measure of the carrier preload has been done. Again, my reasoning here is that carrier preload, as long as it is "snug", shouldn't affect pinion depth that much... agree?.
- At this point, we torqued the cap bolts to 50 lb-ft, rechecked the backlash (it didn't change at this stage on any of our iterations).
- Made sure the paint was spread thin and even (I ended up thinning it with some dub dee farty to make it spread better) and had my buddy put pressure on the ring gear while I turned the flange to get a pattern. One other note: I wiped all the paint off the pinion gear between iterations, which seemed to help with getting a clear pattern.
Below are the patterns I got, please let me know if you would run these, or suggest I try to optimize further:
Drive side:
Coast Side:
