Interaxle Lock

The functionality locks forward drives to rear drive axles, making certain one outer end on each axle is turning in synch. In theory this would work on dry surfaces if the revs of all outer ends are close to identical.

Unfortunately, due to tire wear, this situation of matched tire revs ceases to exist once a vehicle is placed into service. This explains why the interaxle should not be locked during daily highway driving.

As tires wear, their circumference diminishes, resulting in increased revs. Once this occurs, and on a tandem drive it happens rapidly, the mismatch in tire revs can damage the axle gears when they are locked together. There is some forgiveness on slippery surfaces, accounting for why the lock is helpful in inclement weather.

Some of you with AWD or 4WD personal vehicles will be familiar with this. If you need to replace a single tire within the set on your personal vehicle you are commonly told that all four must be replaced. This is due to the same phenomenon, revolution mismatch due to tread wear.

Additionally, if you have ever worked on an AWD truck you will find that closely matching tire revs is required to preserve the transfer case gears. The OEs allow for a mismatch between 1-1.5%. Not certain how they account for tire wear once the vehicle is in service, but you certainly would want to replace all drive tires at the same time, and with a VERY similar tire.

And now….

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