Transmission Trends

How transmission technology has changed the work practices of the fleet technician


FM: What sorts of maintenance issues were you experiencing with manual transmissions?

MH: Especially in the lighter-duty vehicles, with a driver who hasn't had the proper training or experience, you have many issues with the manual transmissions. You're going to have clutch problems, you're going to experience problems with driveshaft failures, and then of course the internal gears inside the manual transmission, because they don't know the proper time to shift and the proper way to shift.

FM: What don't people "get" about manual shifting?

MH: When you get into a Class-8, it does require a skill--and I mean that sincerely--because you have a range in which, from an RPM standpoint, it's ok to shift the transmission. In a tractor, you do not have synchronizers like you do in your lighter-duty vehicles. A synchronizer is like a miniature clutch between the two gears: if you're going from second gear to third, it has friction material that disengages the engine from the transmission. It slows down the transmission because now that you've disengaged it from the engine, that transmission still has an RPM higher than the engine does, because remember that when you go to shift you take your foot off the accelerator pedal. So the synchronizer synchronizes the engine speed and the transmission speed on those lighter-duty transmissions so you have a smoother shift.

On tractors, they never had synchronizers, so it was a fine art for the driver to pause when he went from, say, second gear to third gear. Typically, you would have to double clutch. You engage the clutch, so you disengage the transmission from the engine, you pull the transmission from second gear to neutral, literally--and this is all done in seconds. They let the clutch out really quick, for the engine and transmission to catch up to each other, then they push the clutch back in and they go into third gear.

There's a real skill involved; it's not something you learn overnight. And if you don't do it properly, you can do a lot of damage in a very short period of time and end up costing somebody six or seven thousand dollars--these components are expensive.

FM: From a maintenance operations standpoint, does it make more sense to repair or a replace a faulty transmission?

MH: This will most certainly affect the truck market, and for the most part it already has. Rebuilding components in the shop is becoming a lost art. It's literally gone right out of the business model. The only thing that today typically still gets rebuilt right there in the shop where the truck is parked and has been torn down, is the heavy-duty diesel engine. For the most part, if you take a light-duty vehicle--one of these under 26,000 GVW trucks--they troubleshoot the thing and they say, ‘Ok, this transmission is bad,' and at most places they're going to take that transmission out, they're going to take one off the shelf that's been remanufactured, put it into that truck and give that truck back to the customer.

There are a lot of reasons for that: downtime is very critical, so obviously you can do something like that--what we call "swinging" the component rather than rebuilding--so downtime is drastically reduced. And then you go and send it off to a "clean" atmosphere where you have experts that work on an assembly line and can overhaul that transmission in a shorter amount of time. Obviously that reduces the cost and in the end the remanufactured transmission costs less than it would to have someone rebuild it.

FM: Have maintenance issues been eliminated (or minimized) with the use of automatic and automated transmissions?

MH: Yes, it reduces your downtime and maintenance costs by going to automatics or automated.

In the medium-duty product line, where you typically have the less-experienced driver, we have fewer transmission failures and less clutch work and driveshaft work than we've had in the past, so I can tell you obviously it does help out cost-per-mile.

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