96bulldogpower Posted November 17 Share Posted November 17 Hey guys I have a CHN with Mack rears that snapped a thru shaft last week on the front/rear. I had spare parts at the shop so I waited till I had time to pull them and just got around to installing today. It seemed pretty simple, the shaft snapped and it pushed the half with the yoke straight out of the aluminum seal flange. After replacing the broken parts I turned the output yoke by hand and it spun the front yoke as expected. Unfortunately every so often if I’d spin it faster, it would feel as if something inside would slip as if a spline was stripped or something. I put everything back together and with the power divider unlocked, the truck would spin the rear tires even with the brakes at near full pressure, so it leads me to believe it’s okay? Am I missing something? Would the auto power divider make it behave that way when spinning it by hand? Quote Link to comment https://www.bigmacktrucks.com/topic/76159-broken-rear-differential-thru-shaft-07%E2%80%99-mack-chn/ Share on other sites More sharing options...
Joey Mack Posted November 17 Share Posted November 17 I bet you had the intermediate drive shaft un hooked. If so, that is normal with auto power divider. If you have a locker, and lock it in, it will not slip. 2 Quote Link to comment https://www.bigmacktrucks.com/topic/76159-broken-rear-differential-thru-shaft-07%E2%80%99-mack-chn/#findComment-585687 Share on other sites More sharing options...
96bulldogpower Posted November 19 Author Share Posted November 19 On 11/17/2025 at 4:18 AM, Joey Mack said: I bet you had the intermediate drive shaft un hooked. If so, that is normal with auto power divider. If you have a locker, and lock it in, it will not slip. You’re right! The truck worked for a couple of days since repairing it. No problems since, it was just my paranoia setting in that we broke something else inside. Thank you! 1 Quote Link to comment https://www.bigmacktrucks.com/topic/76159-broken-rear-differential-thru-shaft-07%E2%80%99-mack-chn/#findComment-585807 Share on other sites More sharing options...
Joey Mack Posted November 19 Share Posted November 19 Good deal.. 2 Quote Link to comment https://www.bigmacktrucks.com/topic/76159-broken-rear-differential-thru-shaft-07%E2%80%99-mack-chn/#findComment-585814 Share on other sites More sharing options...
kt_Engineer Posted 1 hour ago Share Posted 1 hour ago On 11/16/2025 at 8:22 PM, 96bulldogpower said: Hey guys I have a CHN with Mack rears that snapped a thru shaft last week on the front/rear. I had spare parts at the shop so I waited till I had time to pull them and just got around to installing today. It seemed pretty simple, the shaft snapped and it pushed the half with the yoke straight out of the aluminum seal flange. After replacing the broken parts I turned the output yoke by hand and it spun the front yoke as expected. Unfortunately every so often if I’d spin it faster, it would feel as if something inside would slip as if a spline was stripped or something. I put everything back together and with the power divider unlocked, the truck would spin the rear tires even with the brakes at near full pressure, so it leads me to believe it’s okay? Am I missing something? Would the auto power divider make it behave that way when spinning it by hand? Unusual to see fatigue failure on the helix thread side of the thru-shaft. The helix thread pumps oil to the powerdivider through the hollow tube that goes around the thru-shaft. Thru-shaft is the easiest part to install. Mack Road train trucks in Australia carry couple of these in the cab as they sometimes snap them in out-back going over dry river-beds. The slipping inside you felt was power-divider doing its job. The cam power-divider is designed to send 3 times the torque to non-slipping axle when it senses slip on one axle. The inner and outer cam are spinning at different speeds when you hand-spun the yoke. I would recommend checking the inter-axle shaft/angle and U-Joints and make sure they are in good condition and will not fatigue the shaft again. Quote Link to comment https://www.bigmacktrucks.com/topic/76159-broken-rear-differential-thru-shaft-07%E2%80%99-mack-chn/#findComment-586527 Share on other sites More sharing options...
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