Truck Repair: International rear end, differential gears, side gears

Question
QUESTION:    We have a 2007 International truck with a 24' box that we use for delivering furniture. The rear end just went out. Although it is under warranty, International claims driver abuse, suggesting that driver was spinning tires on ice or snow till it suddenly caught traction on dry pavement and tore up rear end. We live in Iowa and have lots of snow all winter. Everyone is spinning tires to keep moving. In 30 years I've never had this problem with any delivery truck. Is International just ducking a claim? Have they had a rash of rear ends failing recently? Thanks for your help.

ANSWER: Hi Dave,
Unfortunatley I have not heard of any factory flaws in this area, if the side gears are worn prematurly or there is any evidence of shock load there is no coverage. the only thing I can sugest is if you have a history with this dealer you could speak with the service manager and see if he can give you a break on the price. FYI: when one wheel is spinning the differential gears are twice the speed of the drive shaft which causes the oil to be spun off due to centrifugal force. this causes metal on metal contact and nothing eats metal away quicker than metal on metal. the other thing to keep in mind is when the wheels are spinning and suddenly catch all the rotational weight of the wheels suddenly gets tranfered back into to those little diff gears(spider gears)and the cross shaft. there are certain failures in the drive axle that can only be caused by wheel spin or shock load. ask to see the parts and have the tech explain them to you....if they are pulling your leg they will have a hard time explaining how and why it failed.

Good luck,

Matt

---------- FOLLOW-UP ----------

QUESTION: Thanks Matt,
  The mechanic did mention the term shock load. Can you explain what that means?

Peace,
Dave

Answer
HEY,
shock load means an instant load onto a component much like striking a nail with a hammer...you could put your entire weight onto the nail but it will not go into the wood...however, you can drive a nail into the wood with only a 16oz hammer using shock load. In the same way you can apply a large load to the components in the drive axle, however, instantly applying a small load will cause these components to be overloaded and break....the wheels spinning and then grabbing on dry pavement and instantly loading the drive axle. you would not believe the carnage this will cause to any component on a truck. Unfortunately these failures are considered driver abuse and are not warrantable...but sometimes the dealer may choose to help you with the costs if you have a good professional relationship with them or are a regular customer and they want to retain your business. This is up to the dealer's discretion though. I worked in a transmission shop when I first started in this trade and we had a lot of this failure come through the shop...mostly from gravel trucks spinning through the mud with 40,000lbs on, hitting dry pavement and tearing out driveshafts, tearing off the front half of the diff housing, etc...  Just curious...what parts are broken in the diff?

Matt