MISSISSAUGA, Ont. – When it comes to spec’ing a power take-off unit (PTO) there are literally tens of thousands of choices – each one critical to your unit’s long-term profitability.

In fact, the number of options just keeps growing fueled largely by ever-evolving transmission technology.

While your basic PTO hadn’t changed a lot over the last two decades since Muncie lead the industry from one-piece construction to the now common modular design, the push towards lighter GVWs and a European approach to truck construction brought with them more cramped under-truck envelopes.

“Each product has a niche,” says Ron Kedney, PTO and systems product manager with Drive Products, Inc. (DPI) – the exclusive Canadian agents for Muncie PTOs. And he should know a thing or two about these oft overlooked, yet oh-so-critical, components. In the southern bit of North America, Muncie plays a distant second to Parker Hannifin’s recently acquired Chelsea Products Division in terms of market share. In Canada, however, Drive Products has managed to push this to a near saw-off: practically a 50/50 split.

“Over the last few years the tolerances under the truck have gotten a lot tighter,” says Kedney. “Maybe 15 years ago even, you could basically put a cow beside your transmission there was that much room, now that’s certainly not the case.”

Pointing specifically to the increasing demand for the Allison automatic transmissions, he says the PTO world had to basically go back to the drawing board to find designs able to successfully bolt on to the side.

“Allisons are really gaining popularity in certain garbage and municipal operations and even with the small private grocery-type fleets, for example,” adds Kedney.

Anyone who has ever worked on their cottage’s plumbing would probably understand the dilemma facing a PTO installer – you’ve got to crawl under this, find a way to sneak an eight-inch widget into a six-inch hole, all the while trying to avoid getting in the way of the absolutely critical something-or-other.

When the industry began to embrace these two-pedal trannies, the dilemma only worsened. In Muncie’s case, the answer came in the form of a shaft extension tube-type assembly. Now the technician can find enough wiggle room around frame rails, hoses and a number of obstructions to work the power to the pump.

Engineers know they’re never going to work themselves out of a job, mind you. Every time something changes in a truck’s design, the tolerances are so tight, the preferred power take-off must also be adapted or risk losing its niche.

“A good example would be those new General Motors (medium- and light-duties),” says Kedney. “It’s caused all kinds of development … depending on the exact configuration the frame’s in the way or there’s a spring in the way.”

So it’s back to the drawing board.

Mind you, not all new units take that much design work.

Consider the latest move by the folks at Chelsea in Olive Branch, Miss. A good many Canadians will be getting their wish for a new PTO that is tougher with more torque output capability than any other model currently available.

That’s because Chelsea recently reintroduced its robust 823 Series with enhanced mounting and installation features reports Jeff King, marketing manager for Chelsea Products Division. The product was retired a few years ago, much to the dismay of Canuck haulers, who – let’s face it – tend to require the biggest and strongest trucking components available.

“It was originally taken out of production because we were doing some consolidation,” says King. “The original design of the 823 had four different housings. The shift cover also was integrated right into the housing, so you had no easy way to get in and inspect or check backlash. As a whole, it was a difficult PTO to install.”

Chelsea then decided to introduce the 880 Series as its replacement. It debuted as a kit PTO, which meant it included a shift cover to easily check backlash. Kit designs also simplify shift options because there is no bolt on the cover. Furthermore, input gears are easier to change.

Unfortunately, the 880 Series is available with only enough torque for typical trucking applications, but not quite enough for the likes of a big Mack that’s involved with a chipping operation in Thunder Bay.

“So Canadians should be especially interested in the return of the 823,” said King. “They have many applications where they are pushing our PTOs very hard. That 823 is built like a tank – almost bullet proof.”

The new 823, as a kit design, includes an inspection cover to ease and assist in mounting the units also enabling backlash to be checked easier and faster.

“We’re anticipating that many customers will really push the product to extreme levels, well beyond the normal levels of an eight-bolt PTO,” says King.

But not too far, he cautions.

“One PTO-related trend that we’ve noticed of late originates with the transmission manufacturers,” explains King. “They are now listing maximum torque capabilities for the transmission’s drive gears that mate with our PTOs. They do not want to see these exceeded. In the past we pretty much determined the limits by establishing pitch line velocity standards.”

Among the transmission suppliers now listing torque capabilities are Eaton with the Lightning Series, and Allison on its 1000, 2000 and 2400 Series, as well as the MD and HD Series World transmissions. King also identified Jatco and Aisin automatic transmissions used in Isuzu and Mitsubishi trucks.

“Now they want customers to know the capabilities of the gears so they are not exceeded,” says King. “When they are, problems are likely to occur. So always be certain to check the transmission’s capability before installing one of the 823 PTOs for heavier applications.”

One way to bypass this problem is to go straight to the source and opt for an engine-mounted, factory installed Volvo PTO.

John Moore, a sales engineer with Volvo, explains for typically Canadian PTO applications in snow removal situations the Swedish company’s design is ideal.

“Basically what we offer is a PTO and pump assembly,” he says. “It’s a fixed-displacement, piston-style pump.”

The product range may not reach the ultra-beefy like Chelsea’s 823, but Moore explains with cubic displacements ranging from 61- to 101-cubic-centimetres most applications are easily with the line’s wheelhouse.

“We also offer a split design a lot of people use for snow ploughs,” he adds. “It has two lines out and it’s a 52/52-split, so you can control two things at one time.”

Just the thing if you’ve got to move a big blade around while trying to sling a little sand or salt at the same time.

While it’s similar to a tandem-tandem design, the Volvo unit eliminates the need for a second pump, replacing it with a different bypass valve.

The piston pump offers highly efficient operation since the pistons run with the engine rpm. With a rating of 97 per cent, when the Volvo engine – and yes it is only available on a Volvo power plant – is running at 1,000 rpm, for example, the PTO cranks away at about 970 rpm. Operating speeds this high often lead to cavitation in trannie-mounted systems, but Moore insists, “Cavitation is a rare problem with Volvo’s design,” says Moore.

What is cavitation exactly? Ever been driving a boat with a fast enough outboard motor to get out of the water on a good plane and crank the wheel just a little too hard? You hear what sounds like a suddenly much higher rev to your engine because there is air trapped around your prop. It’s the same basic idea for a PTO, but in this case the pump is moving so fast air separates out of the hydraulic fluid. In this case the cavitation is actually the implosion of a bubble – and it can tear a pump apart.

Admittedly a little pricier than many of its competitors, Moore says you have to consider the true life-cycle cost before making your PTO decision.

“On a dump truck, in that
application body builders will install a PTO and a gear-style pump right to the transmission,” he offers as a for instance. “The downside to that is it’s not clutch independent unless they’re using a hotshift-style PTO.”

At 1,000 rpm if the driver applies the clutch and engages the PTO the gears are going to mesh at that speed and it can be murder on the gears.

“With our system, we’re using a dash-mounted electric over hydraulic switch,” says Moore. “The gears are always meshed.” –

A, Ont. – When it comes to spec’ing a power take-off unit (PTO) there are literally tens of thousands of choices – each one critical to your unit’s long-term profitability.

In fact, the number of options just keeps growing fueled largely by ever-evolving transmission technology.

While your basic PTO hadn’t changed a lot over the last two decades since Muncie lead the industry from one-piece construction to the now common modular design, the push towards lighter GVWs and a European approach to truck construction brought with them more cramped under-truck envelopes.

“Each product has a niche,” says Ron Kedney, PTO and systems product manager with Drive Products, Inc. (DPI) – the exclusive Canadian agents for Muncie PTOs. And he should know a thing or two about these oft overlooked, yet oh-so-critical, components. In the southern bit of North America, Muncie plays a distant second to Parker Hannifin’s recently acquired Chelsea Products Division in terms of market share. In Canada, however, Drive Products has managed to push this to a near saw-off: practically a 50/50 split.

“Over the last few years the tolerances under the truck have gotten a lot tighter,” says Kedney. “Maybe 15 years ago even, you could basically put a cow beside your transmission there was that much room, now that’s certainly not the case.”

Pointing specifically to the increasing demand for the Allison automatic transmissions, he says the PTO world had to basically go back to the drawing board to find designs able to successfully bolt on to the side.

“Allisons are really gaining popularity in certain garbage and municipal operations and even with the small private grocery-type fleets, for example,” adds Kedney.

Anyone who has ever worked on their cottage’s plumbing would probably understand the dilemma facing a PTO installer – you’ve got to crawl under this, find a way to sneak an eight-inch widget into a six-inch hole, all the while trying to avoid getting in the way of the absolutely critical something-or-other.

When the industry began to embrace these two-pedal trannies, the dilemma only worsened. In Muncie’s case, the answer came in the form of a shaft extension tube-type assembly. Now the technician can find enough wiggle room around frame rails, hoses and a number of obstructions to work the power to the pump.

Engineers know they’re never going to work themselves out of a job, mind you. Every time something changes in a truck’s design, the tolerances are so tight, the preferred power take-off must also be adapted or risk losing its niche.

“A good example would be those new General Motors (medium- and light-duties),” says Kedney. “It’s caused all kinds of development … depending on the exact configuration the frame’s in the way or there’s a spring in the way.”

So it’s back to the drawing board.

Mind you, not all new units take that much design work.

Consider the latest move by the folks at Chelsea in Olive Branch, Miss. A good many Canadians will be getting their wish for a new PTO that is tougher with more torque output capability than any other model currently available.

That’s because Chelsea recently reintroduced its robust 823 Series with enhanced mounting and installation features reports Jeff King, marketing manager for Chelsea Products Division. The product was retired a few years ago, much to the dismay of Canuck haulers, who – let’s face it – tend to require the biggest and strongest trucking components available.

“It was originally taken out of production because we were doing some consolidation,” says King. “The original design of the 823 had four different housings. The shift cover also was integrated right into the housing, so you had no easy way to get in and inspect or check backlash. As a whole, it was a difficult PTO to install.”

Chelsea then decided to introduce the 880 Series as its replacement. It debuted as a kit PTO, which meant it included a shift cover to easily check backlash. Kit designs also simplify shift options because there is no bolt on the cover. Furthermore, input gears are easier to change.

Unfortunately, the 880 Series is available with only enough torque for typical trucking applications, but not quite enough for the likes of a big Mack that’s involved with a chipping operation in Thunder Bay.

“So Canadians should be especially interested in the return of the 823,” said King. “They have many applications where they are pushing our PTOs very hard. That 823 is built like a tank – almost bullet proof.”

The new 823, as a kit design, includes an inspection cover to ease and assist in mounting the units also enabling backlash to be checked easier and faster.

“We’re anticipating that many customers will really push the product to extreme levels, well beyond the normal levels of an eight-bolt PTO,” says King.

But not too far, he cautions.

“One PTO-related trend that we’ve noticed of late originates with the transmission manufacturers,” explains King. “They are now listing maximum torque capabilities for the transmission’s drive gears that mate with our PTOs. They do not want to see these exceeded. In the past we pretty much determined the limits by establishing pitch line velocity standards.”

Among the transmission suppliers now listing torque capabilities are Eaton with the Lightning Series, and Allison on its 1000, 2000 and 2400 Series, as well as the MD and HD Series World transmissions. King also identified Jatco and Aisin automatic transmissions used in Isuzu and Mitsubishi trucks.

“Now they want customers to know the capabilities of the gears so they are not exceeded,” says King. “When they are, problems are likely to occur. So always be certain to check the transmission’s capability before installing one of the 823 PTOs for heavier applications.”

One way to bypass this problem is to go straight to the source and opt for an engine-mounted, factory installed Volvo PTO.

John Moore, a sales engineer with Volvo, explains for typically Canadian PTO applications in snow removal situations the Swedish company’s design is ideal.

“Basically what we offer is a PTO and pump assembly,” he says. “It’s a fixed-displacement, piston-style pump.”

The product range may not reach the ultra-beefy like Chelsea’s 823, but Moore explains with cubic displacements ranging from 61- to 101-cubic-centimetres most applications are easily with the line’s wheelhouse.

“We also offer a split design a lot of people use for snow ploughs,” he adds. “It has two lines out and it’s a 52/52-split, so you can control two things at one time.”

Just the thing if you’ve got to move a big blade around while trying to sling a little sand or salt at the same time.

While it’s similar to a tandem-tandem design, the Volvo unit eliminates the need for a second pump, replacing it with a different bypass valve.

The piston pump offers highly efficient operation since the pistons run with the engine rpm. With a rating of 97 per cent, when the Volvo engine – and yes it is only available on a Volvo power plant – is running at 1,000 rpm, for example, the PTO cranks away at about 970 rpm. Operating speeds this high often lead to cavitation in trannie-mounted systems, but Moore insists, “Cavitation is a rare problem with Volvo’s design,” says Moore.

What is cavitation exactly? Ever been driving a boat with a fast enough outboard motor to get out of the water on a good plane and crank the wheel just a little too hard? You hear what sounds like a suddenly much higher rev to
your engine because there is air trapped around your prop. It’s the same basic idea for a PTO, but in this case the pump is moving so fast air separates out of the hydraulic fluid. In this case the cavitation is actually the implosion of a bubble – and it can tear a pump apart.

Admittedly a little pricier than many of its competitors, Moore says you have to consider the true life-cycle cost before making your PTO decision.

“On a dump truck, in that application body builders will install a PTO and a gear-style pump right to the transmission,” he offers as a for instance. “The downside to that is it’s not clutch independent unless they’re using a hotshift-style PTO.”

At 1,000 rpm if the driver applies the clutch and engages the PTO the gears are going to mesh at that speed and it can be murder on the gears.

“With our system, we’re using a dash-mounted electric over hydraulic switch,” says Moore. “The gears are always meshed.” –

Powerful problems

Five issues can potentially plague PTOs in almost any application, but a fleet or owner/op in the know can easily troubleshoot its investment before premature failure or other serious damage occurs.

PTO related noise: The amount of backlash determines how well the PTO gears will mesh with those of the transmission. When the tolerance varies too far – which is a minuscule amount in truth – the teeth begin to wear prematurely.

A dead giveaway when this occurs will be the noises generated by the unit. A whine and tolerances are too tight leading to problems at the root of the gear teeth. A rattle like spinning a jar of marbles, on the other hand, means the tips of the teeth are exposed to needless wear.

By simply changing the gasket between the PTO and the transmission, the backlash is adjusted eliminating either condition.

Engine vibration: As with many drivetrain components, PTOs are susceptible to damage caused by torsional vibrations associated with today’s engines. If you’re hearing that earlier mentioned rattle, rev the engine. If the rattle goes away, it’s likely a vibration issue and some form of dampening device might be needed.

Shift-related concern: When using an air-shift system, the most common spec today, if the PTO becomes difficult to engage, there is likely a problem with the air system. Check for kinks otherwise the bearing side of the teeth will experience premature wear.

Conversely, if disengaging is when you have a problem it’s likely the spring used to pop the gears away from the transmission has outlived its usefulness. A warning light, if properly functioning, will tip the operator to the problem otherwise the pump will face over speeding and cavitation among other issues.

Improper lubrication: When dealing specifically with automatic transmissions, the PTO often bolts on at either the three or nine o’clock position which can compromise lubrication. A squealing noise should signal the operator the bearings are tightening and may eventually seize.

In this case there is a proactive fix highly recommended by manufacturers. The addition of a pressure lube idler shaft will draw fresh lubricant to the bearing ensuring long life.

Wrong from the get go: If a PTO or auxiliary shaft is improperly spec’d by the owner, it’s never going to work right. Talk to the experts and make sure you have a unit matched to your transmission and application.

As well, significant property damage, personal injury or even death can result from the failure to periodically inspect and maintain the PTO and auxiliary power system. Power takeoff units and their components experience severe vibration during operation, which can cause problems such as bolts loosening, components leaking and the like.

– Source: Jeff King, marketing manager for Chelsea Products Division

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