(This may also be relevant to M5500DT and M7500DT)
The front axle pivots aren’t greaseable in stock form and when they wear, they put the front diff input shaft (pinion shaft.. whatever) out of alignment with the prop shaft. This accelerates the wear of the splines on the input shaft, the splined couplings and the prop shaft.
The original pivot bearings of DU PTFE/bronze/steel dry-type bushes depend on O-rings to protect them. To avoid future problems a tractor mechanic recommended dropping the front axle and manually greasing the bushes and couplings every front axle oil change (800 hours). This isn’t a huge job (maybe a couple of hours - the axle needn’t be completely removed, and the steering linkage keeps the wheels pointed the right way and stops the wheels from falling over) and probably good value considering the ultimate cost of not doing it. Some parts are discontinued items – depending on where in the world you are – so occasional preventive maintenance could make the difference between 4WD functionality and no 4WD.
With the high cost of getting a new pinion and ring gear (sold only as a set) out of the US, questionable used units, and the pinion gear and ring gear being in excellent condition I decided to chance getting the pinion splines repaired. The pinion shaft seems to be something like AISI 4140 in its natural state. It’s hardened at each end (gear end/bearing journals and the splined end.
A machine shop cut off the splined end at the non-hardened section, creating a locating spigot, welded a new end on with pre-heat and post heat, and cut the splines to match the coupling. The coupling was available locally as a new part. Then the splined end of the shaft was induction hardened. The complete pinion job cost NZ$1500+tax. (Module m = 2 mm, 13 teeth, 30-degree pressure angle, 15.83mm over 3 teeth)
The machine shop strongly recommended using a good moly grease on the splines. I’d make that part of the 800 hour PM.
So far it has worked OK, but early days yet because I think that the main failure mode would probably be fatigue.
The pinion bearing assembly had next to no preload when I removed it, the Koyo bearings showed signs of wear but no pitting or flaking. I replaced the bearings (not available from Kubota, got high capacity NTN bearings), and hand-lapped the end of the solid spacer to get the right pre-load. The lapping process was basically the same as used for lapping steel nozzles and discs on high pressure steam safety valves, except I used 600 grit wet and dry rather than lapping paste.
Data from a couple of sources including Timken indicated that increase in diff pinion preload torque is approximately proportional to the decrease in preload spacing. For the Kubota I found that each 0.1mm decrease in spacer increased torque by about 1.1 N.m (7.5kg using the “string-around the shaft” method).
I didn’t need to change the shims on the diff input pinion shaft, the pattern was pretty much perfect. (Most informative info on patterns I found was the Yukon Gear blog}.
I hope the above is useful to someone, one day.
As with my recent kingpin overhaul write-up, let me know if you have any corrections/concerns/constructive suggestions.
The front axle pivots aren’t greaseable in stock form and when they wear, they put the front diff input shaft (pinion shaft.. whatever) out of alignment with the prop shaft. This accelerates the wear of the splines on the input shaft, the splined couplings and the prop shaft.
The original pivot bearings of DU PTFE/bronze/steel dry-type bushes depend on O-rings to protect them. To avoid future problems a tractor mechanic recommended dropping the front axle and manually greasing the bushes and couplings every front axle oil change (800 hours). This isn’t a huge job (maybe a couple of hours - the axle needn’t be completely removed, and the steering linkage keeps the wheels pointed the right way and stops the wheels from falling over) and probably good value considering the ultimate cost of not doing it. Some parts are discontinued items – depending on where in the world you are – so occasional preventive maintenance could make the difference between 4WD functionality and no 4WD.
With the high cost of getting a new pinion and ring gear (sold only as a set) out of the US, questionable used units, and the pinion gear and ring gear being in excellent condition I decided to chance getting the pinion splines repaired. The pinion shaft seems to be something like AISI 4140 in its natural state. It’s hardened at each end (gear end/bearing journals and the splined end.
A machine shop cut off the splined end at the non-hardened section, creating a locating spigot, welded a new end on with pre-heat and post heat, and cut the splines to match the coupling. The coupling was available locally as a new part. Then the splined end of the shaft was induction hardened. The complete pinion job cost NZ$1500+tax. (Module m = 2 mm, 13 teeth, 30-degree pressure angle, 15.83mm over 3 teeth)
The machine shop strongly recommended using a good moly grease on the splines. I’d make that part of the 800 hour PM.
So far it has worked OK, but early days yet because I think that the main failure mode would probably be fatigue.
The pinion bearing assembly had next to no preload when I removed it, the Koyo bearings showed signs of wear but no pitting or flaking. I replaced the bearings (not available from Kubota, got high capacity NTN bearings), and hand-lapped the end of the solid spacer to get the right pre-load. The lapping process was basically the same as used for lapping steel nozzles and discs on high pressure steam safety valves, except I used 600 grit wet and dry rather than lapping paste.
Data from a couple of sources including Timken indicated that increase in diff pinion preload torque is approximately proportional to the decrease in preload spacing. For the Kubota I found that each 0.1mm decrease in spacer increased torque by about 1.1 N.m (7.5kg using the “string-around the shaft” method).
I didn’t need to change the shims on the diff input pinion shaft, the pattern was pretty much perfect. (Most informative info on patterns I found was the Yukon Gear blog}.
I hope the above is useful to someone, one day.
As with my recent kingpin overhaul write-up, let me know if you have any corrections/concerns/constructive suggestions.
