A 13-speed transmission exhibits wear in the shift fork on the yoke bar that shifts the splitter and in the shift collar surfaces. The most likely problem is:

• A. A bad air seal in the overdrive shift unit
• B. Engagement of overdrive while the transmission is in low range
• C. The driver preselects the splitter button, flipping it and then failing to complete the shift until some time later
• D. Transmission lube oil diluted with water

Answer: (C)

When you see wear on the shift fork that moves the splitter and on the mating surfaces of the shift collar, it points to improper shifting timing rather than a mechanical failure of the gear train itself. In a 13-speed with a splitter, the splitter is engaged by a dedicated fork that slides a collar into the splitter gears. If the operator preselects the splitter and then fails to complete the shift promptly, the fork and collar encounter transitional loading or hold-at-midposition conditions. That repeated partial engagement etches surfaces and creates wear patterns on the yoke bar and the shift collar where they contact each other.

Other scenarios would show different symptoms. An air seal problem in the overdrive shift unit affects the overdrive mechanism specifically, not the splitter linkage wear. Engaging overdrive while in low range would cause a harsh or impossible shift but doesn’t typically produce the localized wear pattern on the splitter’s fork and collar surfaces. Lubricant contaminated with water causes general wear and corrosion across multiple components, not the targeted wear on the splitter shift parts.

So the wear described is most consistent with the driver preselecting the splitter and then delaying the shift until later, leading to abnormal, late engagement and repeated contact under imperfect alignment.