Trailer Life August 2005
photography Larry Walton
Banks’ billet torque converter takes on big diesel power
I have to admit to getting a certain thrill from pulling a sizable trailer over a long, steep grade while staying ahead of my fellow trailer-toting RVers. There’s just something about the combination of load and power that makes you feel really good.
But, as is so often the case in life, the very things you like the most can often cause the most trouble.
When it comes to towing, load and power and the resultant heat build-up are the very factors that wreak the most havoc on a torque converter as it transfers power from the engine to the transmission.
In general, manufacturers do not build stock torque converters to withstand the abuse – beyond design limits – that many owners put them through. These include overloading, performance enhancements and exhaust brakes – and sometimes it’s all three.
A torque converter’s job is to provide a fluid coupling that allows the engine to continue running when the vehicle is stopped in gear. Because the inverter and turbine that respectively push and receive the fluid can never achieve a solid lockup, most torque converters also have clutches that engage to make a mechanical connection between the engine and the transmission for maximum powertrain efficiency and minimum heat buildup.
Factory-issue clutch compounds in stock converters work fine when the engine is stock or loads conform to ratings. But add more horsepower, more torque and a heavy load beyond the factory recommendations and clutches can start slipping under the extra strain. This slipping causes friction that produces heat – which the stock converter cover is ill-equipped to handle. This situation is particularly acute when the truck is outfitted with aftermarket equipment that boosts engine horsepower and torque well in excess of factory specifications, or when the load is a trailer that exceeds the factory tow rating.
According to John Domaschofsky of Dan Judy Automotive in Salem, Oregon, where they’ve been rebuilding automatics and replacing broken torque converters for more than 30 years, “When the clutches start burning, there’s so much heat generated that it turns the outside of the torque converter bright blue.”
The heat also causes the torque-converter housings to deform or balloon. This ballooning causes wider clearances which, in turn, create higher stall speeds that produce even more heat. A deformed torque-converter housing also reduces the clutch surface area, causing more slip, more heat and more debris. Torque-converter ballooning can also lead to thrust-bearing failures in some engines, although this is generally more of an issue with gasoline-powered motorhomes, and the Ford diesels have shown no such record. “Debris in the transmission fluid is from the heat damaging the seals and plastic pieces in the transmission,” says Domaschofsky, who has spent a lot of years repairing automatic transmissions and replacing torque converters.
Heat also causes fluids to degrade. “The transmission and the torque converter share fluid,” elaborates Domaschofsky. “When the converter starts to fail it will produce material that will contaminate the transmission. The fluid comes out of the torque converter and into the cooling system.”
“As the torque converter and transmission begin their downward death spiral, material can get caught and plug the cooling system. This, of course, causes even more heat build-up.”
Fluid that is returning to the transmission from the cooling system gets dumped onto the planetary gears. “Any material that happens to be in the fluid goes directly onto the gear surfaces. This is why it’s not a good idea to keep running a damaged or inadequate torque converter. In all the years I’ve been in the business, I’ve never seen a torque-converter failure that has not caused damage to the transmission,” says Domaschofsky.
So, it’s fitting that Gale Banks Engineering, which is responsible for its share of the aftermarket diesel power out there on the road, developed a special high-performance billet torque converter that can handle the newfound power.
We tested the Banks Billet Torque Converter (part No. 72521; $995 plus $250 core charge) in a Ford F-250 Super Duty with a 7.3-liter Power Stroke that has been upped in power output. Along with the new torque converter, we installed a Banks TransCommand unit to beef up clutch-line pressures.
The Banks torque converter features a billet cover manufactured to maintain its structural integrity under extreme heat and mechanical stress. On most pickups, the portion of the stock torque converter that is bolted to the engine flex plate is a stamped-steel housing with welded-on tabs, which can deflect or distort the housing under sustained high loads such as those induced by engines with boosted power output or overweight trailers. This distortion usually causes high spots on the machined metal surface that is engaged by the lockup clutch. With less metal surface contacting the clutch surface, clutch slippage, dust and heat multiply in a vicious cycle.
Banks addresses these issues by using a one-piece billet cover that is precision-machined. This billet construction reduces flex, thereby retaining clutch contact surface even under heavy loads. This means quicker, surer lock-up and less slippage which, in turn, helps prevent heat, wear and fluid contamination.
Other features of the Banks converter that make it tougher also improve performance. For example, stock inverter and turbine blades are held in place by small tabs that protrude through a slot. The tabs are bent over to hold them in place. These fins can become loose and diminish in efficiency when subjected to high loads.
The fins in a Banks torque converter are furnace-brazed in place to prevent loosening caused by high power and weight loads. Furnace brazing creates a much stronger bond to withstand the rigors of heat and fluid pressure; a similar process is used on jet engine parts.
The Banks dual-disc clutch maximizes surface area to reduce slippage under the combination of high torque and heavy load. Carbon-ceramic clutch materials improve on the stock cellulose-based paper material, meaning less clutch material is being ground off of the plates and into the automatic-transmission fluid (ATF).
We started by installing a transmission-oil-temperature gauge because fluid temperatures are one of the best indicators of what is going on with the torque converter. In fact, a transmission-oil-temperature gauge is a good idea for anyone who pulls heavy loads and/or has significantly increased the power output of their tow vehicle.
We installed the sensor for the temperature gauge in the line near where the fluid leaves the transmission before going to the cooler. This location gives a better read on torque-converter activity instead of just how well your transmission cooler is working. Trailer Life advises putting the sensor in the pan for a number of reasons (most gauges are calibrated for pan temperatures, and pan temperatures are what the transmission gets), but as important as the location of the gauge is that you have one, and a good baseline for keeping an eye on ATF temperature.
We monitored transmission temperatures under several conditions including town driving, highway cruising, and acceleration runs. As expected, transmission temperatures went up when the torque converter was working the hardest in stop-and-go traffic and under heavy acceleration.
Torque converters are happiest when locked-up and cruising. In fact, the experts we talked to said the hottest conditions for your torque converter are at low speeds with a load – like backing up into a camping spot or pulling a steep incline from a stop – and those conditions where a manual transmission would need to slip the clutch to get going or change gears.
Our tests showed slightly lower transmission temperatures with the Banks setup. On average, the temperatures were 5°F lower under a variety of conditions with the Banks equipment installed.
We ran a series of tests while towing a 7,000-pound trailer, first with the stock torque converter, and then with the Banks TransCommand and billet torque converter installed.
Our initial fuel-consumption tests saw no measurable changes between the two setups. This is not surprising because we towed a 7,000-pound trailer at a highway cruising speed of 65 MPH. Both the stock and the Banks torque converters would have been in lock-up mode in these conditions, which means the clutches were producing a good non-slip connection between the engine and the transmission.
With a longer-duration fuel-economy test we would expect to see fuel-economy improvements in stop-and-go conditions with the Banks converter because with a lower stall speed and quicker shifts, it should take less fuel to get things moving. This is based on our personal experience because dynos programmed for stop-and-go driving tend to reside at the Environmental Protection Agency, and a trailer makes no difference unless the dyno is programmed for the additional loads.
Also, under a heavier load, when you are really pouring some diesel to it (like on a steep grade), you should also see some fuel improvements and slightly lower temperatures as slippage in the torque converter is reduced with the Banks upgrade.
ACCELERATION WITH ATTITUDE
Our muscled-up F-250, towing the trailer while using the stock torque converter, averaged a 0-60 MPH acceleration time of 15.4 seconds. During the tests we noticed a considerable amount of shudder, which we attributed to slippage in the torque-converter clutches, although shudder under load can also come from other sources.
With the new Banks torque converter installed, the average 0-60 MPH acceleration time was 14.7 – a 0.7-second improvement. While clutch shudder was nearly eliminated, another problem arose: With the new torque converter, there was a significant increase in wheel spin, even with the heavy trailer-tongue weight. That shows how much more power the billet converter is putting to the rear wheels compared to the stock unit. Most of the advantage in acceleration will occur once the vehicle’s rolling and tire slip is minimized; if you tow a heavy fifth-wheel this should not be an issue.
During our acceleration tests we also recorded 40-60 MPH times. The average 40-60 MPH time with the stock torque converter was 8.5 seconds. The average 40-60 MPH time with the Banks Billet Torque Converter and TransCommand combination was 7.6 seconds. This represents an improvement of nearly a full second in those on-ramp spurts.
We found that the lower stall speed of the new torque converter was noticeable in normal driving conditions. Or, in layman’s terms, it takes less throttle input to get things moving. We also noticed the F-250 shifts quicker and firmer under hard acceleration.
Because the new converter was installed to improve durability and protect the transmission, we were pleasantly surprised by the improvement in acceleration and driving fun. Any improvements in fuel economy will likely be negated by the urge to stand on the throttle more often.
The torque converter could be installed by a skilled backyard mechanic in about a day. The instruction manual that comes with it is quite detailed, but the recommended tools list has some specialized items, like transmission hoists, a flywheel rotating tool and a torque-converter holding tool.
Shop labor costs for installing the Banks Billet Torque Converter in this truck run from $370 to $530; variables include location, two- or four-wheel drive and so on. Shop installation of the TransCommand costs about $75. That brings the whole job, with parts and labor, in at about $1,725.
Parts and labor for another stock torque converter ranges from $824 to $972, but keep in mind if you wait for the original to go out the transmission will likely need some work as well.
The Banks Billet Torque Converter and TransCommand is an effective combination for those who are hauling heavy loads and/or have increased the power of their trucks with performance upgrades.
Gale Banks Engineering highly recommends installing its TransCommand (part No. 62570; $277) transmission command module along with the Banks Billet Torque Converter. The truck computer monitors throttle position and rate of acceleration to determine load and accordingly increase or decrease line pressure. This produces a smoother shift under light load, and firmer shifts under heavy load to prevent clutch slippage.
Banks developed the TransCommand to complement its other performance parts because with more power the truck will accelerate with less throttle, making the computer think it’s time for smooth shifts when the increased power actually calls for firmer shifts.
The TransCommand senses load conditions to accelerate line-pressure ramp rates. This provides firmer shifts under higher power and bigger load conditions. While the stock line pressures offer a smooth and comfortable shift, a firmer shift is often desirable when towing or when performance modifications have increased engine power. These conditions produce increased clutch slippage, which can cause heat degrading of fluid and can deposit particles that damage the transmission. In addition to extending torque-converter and transmission life, the TransCommand is designed to increase performance by reducing or eliminating slippage in the torque converter. Instead of wasting energy in internal friction, it supplies more consistent power to the wheels. – L.W.
While You’re There
While the truck is on the rack and the drivelines are disconnected, it’s a good idea to check the conditions of the U-joints, drive shafts and seals. U-joints can be tested while hooked up to see if they are solid, but they need to be tested while disconnected to see that there are no catches or stiff spots.
During our inspections we found some worn teeth on the starter ring gear, which was replaced along with the flex plate while it was accessible during the torque-converter install. This replacement costs about $25 in additional labor while you’re already there, compared to more than $400 if you had to go back in and do it as a separate repair. – L.W.