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10 Myths About:Transmissions

What The Other Guys Never Told You

Larry S. Saavedra
Jul 1, 2009
Some trucks may look rugged and battle-proven, but under that formidable body hides a weak link-the transmission. Admittedly not all trucks have a predisposition to premature transmission failure and can run for 100,000 miles or more without a hint of trouble. However, the overall thought of transmission fatigue is always lurking in the back of our minds, especially when we substantially increase horsepower and torque beyond stock and tow heavy loads regularly.
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The stories we've written in past issues of 8-Lug have mostly been associated with some sort of transmission hop-up kit-from complete valvebody reconstruction to torque converter upgrades. While important issues to discuss, these stories targeted specific transmission types and ways to improve their reliability. We never really discussed transmissions in a general sense, leaving some readers still mystified by this critical component of the truck.
For those readers, we've decided to put together a Top 10 list of myths often associated with transmissions. While there are plenty of performance transmission providers in the aftermarket that do miracle work on our vehicles, we contacted ATS in Denver, Colorado, to try to bust some of the myths about transmissions in general
As you know, ATS is a leading performance transmission company for diesel truck enthusiasts. ATS has been at the forefront of the sled-pull scene and has taken that motorsports knowledge and applied it to some of the toughest street transmission upgrades available today. Want more info? Contact ATS Diesel at 866-454-9539, www.ATSdiesel.com/8lug.
Here are ATS's responses to our Top 10 questions about transmissions:
1 Myth:
Transmission fluid is best left untouched. If you don't begin a cycle of servicing the fluid, chances are you will not have to ever worry about it. Synthetic fluid in particular does not require changing.
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Reality:
As the gears and internal parts turn (and the torque converter, if running an automatic transmission), fluid shearing occurs and viscosity is lost over time. Once the fluid loses its lubrication abilities (and/or the additive package wears out), the clutch, frictions, and contacting parts will wear and that will eventually cause more damage to the transmission.
2 Myth:
Performing a suck-flush on a transmission-where the fluid is removed from the unit by suctioning it out through the fill tube-is the best way to service it.
Reality:
Transmissions on light-duty diesels use a filter media to trap and collect debris that is naturally shed by the gears and clutch packs as they turn inside the unit. Many of these vehicles' filters require the transmission pan to be removed in order to replace it-so simply suctioning out the fluid does not address this. These filters should be replaced routinely in order to provide adequate fluid flow through the media and to check the condition of the transmission by looking for excessive debris.
3 Myth:
An upgraded transmission is indestructible and negligence and abuse such as neutral-dropping will not cause damage as it would to a stock unit.
Reality:
Even the heaviest-duty transmission can be damaged. Conventional transmissions rely on shafts to transfer the energy from the clutch or torque converter to the gear sections. Sudden shocks or prolonged strain can snap these shafts and render the transmission inoperable. Likewise, not servicing an upgraded or heavy-duty transmission will eventually lead to its demise.
4 Myth:
Performance torque converters require raising the stall speed or the rpm level of maximum power transfer for the converter's fluid coupling system.
Reality:
While some situations and vehicles are enhanced by raising the converter's fluid coupling stall speed, many diesel trucks actually benefit from a slightly lowered stall speed. Torque converters such as the Five Star often feature a lower-than-stock stall speed to produce energy transfer efficiency at the peak rpm torque of the motor. When the torque converter switches from fluid coupling to 1:1 lockup mode, the transition is made smoother, partially by using a lower stall (depending on the truck's engine speed).
5 Myth:
The best material and only type to consider for performance torque converter clutches is always Kevlar.
Reality:
Often the application of the torque converter and the power output of the vehicle, as well as the type of transmission fluid used, will cause a different type of clutch material (other than Kevlar) to be the best choice. Many times clutch materials for lockup-style automatic transmission torque converters will consist of composite media that uses a certain percentage of paper or other elements such as carbon. This ensures the clutch system in the torque converter provides the optimum coefficient of friction to maintain torque-holding ability.
6 Myth:
Diesel trucks produce too much torque for automatic transmissions to handle reliably.
Reality:
Modern automatic transmissions have evolved significantly on late-model diesels and have the capability to handle vast amounts of torque now. Some manufacturers are now offering certain model vehicles exclusively with automatic transmissions. Upgraded transmissions for diesel pickups can now be built to run neck and neck with most manual transmissions, as the manual trans will still have the limitation of the clutch where slippage becomes a factor.
7 Myth:
Band adjustments are required when servicing any light-duty truck transmission.
Reality:
Some diesel owners find themselves getting taken to the cleaner when bringing their truck to a shop for transmission service. Late-model truck owners should be aware that their transmission might not need some services, such as band adjustments. While earlier-model transmissions still made use of the standard bands wrapped around each gear section, late models use a different gear configuration and will not need the band adjustment procedure performed when servicing (i.e. an owner of an '07 Dodge Cummins should be skeptical of a shop that states a band adjustment will be performed on his 68RFE automatic transmission).
8 Myth:
Hard shifting is always best or always required to handle upgraded power on a performance-built transmission.
Reality:
While more positive shifting is commonly used on earlier-model truck transmissions, late-model transmissions use different technology, including progressive line rise. This means during the initial shifting of gears, the hydraulic pressure being applied to the clutch pack in the transmission is lower and is then ramped up increasingly as the torque load amplifies. Also, later-model trucks incorporate a larger number of gears and closer gear ratios that make for a less severe rpm jump during the shift.
9 Myth:
Transmission replacement is a nightmare because it is not known whether the replacement unit will shift and function properly once it is installed in the truck, and it must be installed in the truck to test its operation.
Reality:
Higher-end transmission suppliers and manufacturers use equipment such as transmission dynamometers and valvebody dynamometers to simulate the routines they would perform in the actual truck. These dynamometers run the unit through each shift and test hydraulic pressures multiple times at varied engine loads and give computer feedback to ensure proper operation and performance.
10 Myth:
Transmissions built for racing and sled pulling applications should have no bearing on one's desire to purchase a heavy-duty transmission for trailer pulling and/or work applications.
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Reality:
Companies that have experience with building transmissions to stand up to the punishment of racing and sled pulling have an advantage when it comes to producing the best trailer towing transmission. Since the same model transmissions are typically used in both scenarios, the tougher components designed for competition can be used in a transmission built for towing and provide ultimate longevity and performance for everything from daily driving to work situations.

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