I changed the axles on my 646 from the long LBH axles to 446 axles. I installed normal OEM 15 inch wheel loader wheels with OEM size tires. I checked the end play and added an OEM shim on one side to get it to spec. I drove it around for 30 minutes and opened the transaxle cover to replace the seal on the hi/low shifter. The end of the differential case half into which the axle slides was cracked. It was the one to which I added the shim. The diffential case bolts were intact and the nuts were tight. Does anyone have any idea what could have caused this?