This inexpensive (OEM allowed) specing error can cause this
Gary Hey- Apr 25
- 2 min read
All tandem axle TRACTORS with 4S/4M, are subject to a fwd drive axle Spin Out Failure given ATC (Automatic Traction Control) with ESP/ESC/RSC. It's the same on tandem trucks with ATC.
If one or more outer end spin faster than the steer tires, drive brakes are applied where necessary using ATC, moving power to the other side. 4S/4M has 2 sensors/modulators on the steer and 99% of the time, 2 located on the rear rear axle. No S/M on the fwd rear. It takes braking signals from the rear rear, so RSD (Reduced Stopping Distance) does not require 6S/6M. 4S/4M works fine when braking.
4S/4M ATC tandem is in the mud/sand/snow/ice/wet pavement, etc. If the rear rear is spinning under power, then both brakes are applied right or left as required, however, if the forward drive spins, no brakes are applied. Driver hammers down, resulting in failure. This is not the fault of the axle, it’s 4S/4M and the driver.
Tractors with 4S/4M or a truck w/ATC, requires driver education. Locking the interaxle for the most part solves the problem, but not completely. FYI, locking the interaxle when moving can cause a shock load.
OEM’s should not offer 4S/4M on any tandem chassis (truck/tractor) with ATC. Tridems are also subject to this failure, even though they have 6S/6M. We'll address these next week.
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