Medium Duty: Transmission and PTO Upkeep

Maintaining transmissions and PTOs is serious business.


Technicians who follow basic maintenance procedures should have no problems with PTOs, says Douglass.

“Read the installation manuals thoroughly, follow all the steps and pay particular attention to the wiring, especially if it’s an automatic transmission,” he says. “Because those are the areas where installers have the most problems, and those tend to be the areas, from a maintenance standpoint, where after time, things start to act up, if wiring connections aren’t good or become corroded, the PTO starts to behave erratically, that’s usually an indication of an electrical problem.”

NTEA’s Johnson says the first thing to do when you put a new truck in service is to check the backlash—the free movement between two meshing gears on the PTO.

“I know (the PTO) was installed by a so-called professional who should know what they’re doing, but that doesn’t guarantee they do,” he says. “If (the PTO is) too tight, you’re going to burn the PTO drive gear up; if (it’s) too loose, you’re going to get a lot of noise and gear damage. Also, check if they’re air or electric shift; make sure they’re shifting properly.”

For manual transmissions, technicians will have to put a clutch in, which requires some additional work, Johnson says.

“You have to remove the PTO in the process of changing out the transmission because it’s usually in the way,” he says. “When they bolt it back up, they put it back in the exact same (place). That’s a good starting point; you should double-check the mesh of the gears. If you’ve done any work on the transmission—changed bearings, replaced components—it becomes especially critical to re-check the shimming of the PTO, just to make sure they’re meshing properly.

“Chances are it will be, but every now and then it may get torqued a little tighter, the gasket could have crushed a little, or the new gasket has a little bit different thickness than the old gasket,” Johnson says. “Anytime you remove a PTO from a transmission, when you re-install it, double-check the shifting to make sure it’s shifting properly, double-check the backlash of the gears to make sure it’s shimmed properly, things of that nature.”


While the PTO market has not changed drastically, there has been a significant shift in transmissions, with automatic and automated options becoming much more prevalent in medium-duty work trucks,

Johnson says, so lesser experienced drivers can handle them with more ease.

“If you’re a power company, you hire a lineman or a cable splicer, you don’t hire a truck driver,” he says.

Allison Transmission manager of service technology Keith Duner says the company has adapted its products to account for these operators.

“If you look at all the different vocations that are running down the street, most do not have trained truck drivers operating them, so you have the ability to stick someone in a vehicle who is less than a fully trained, 8-12-14-speed capable truck driver and sit behind the wheel of something that drives like the family automobile,” he says. “And the safety inhibits that are inherent in both the physical design and the electronic control system, further protect (against) operator abuse.”

Duner says while the driver shortage has hastened the acceptance of automatics, it is important to distinguish between automatic and automated.

“Automated manual transmissions are not automatics, as they still have a clutch to maintain or burn up,” he says.


Dontia Warren, NAFTA medium-duty market development and strategy manager for Eaton Truck Components, says automated transmissions like their UltraShift HV can increase driver safety while reducing fatigue from shifting, particularly in urban environments.

“What it does for that driver… is remove the clutch pedal from the cab, it removes the shift lever, and they simply maneuver the throttle and the brake,” she says. “By taking an automated approach versus going to an automatic, you’re going to have fuel efficiency gains with our products that you would not be able to realize with an automatic transmission.”

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