Introduction to the 6R140 Transmission:
If you’ve been around Next Gen for a while, you likely know all about our passion for the 6R140 transmission and how to make it better. What you may not know, is all of the changes made to this generally stout unit to ensure it’s ability to hold added power and live a healthy lifespan.
Off the factory floor, the 6R140 has a variety of “Pro’s”, things such as it’s dual planetary gearsets, massive output shaft and large diameter clutches. These all aid in creating a transmission that has an excellent foundation for upgrade and enhancement.
Unfortunately however, it is one of our most popular lines of transmission. This highlights it as a probable failure point behind ever increasingly more powerful motors, both gas and diesel. In this installment of our ever popular Drivetrain 101 series, we will be assessing all of the woes and benefits of this polarizing unit of engineering. Let’s proceed!
A Brief History of the 6R140 Transmission:
This big brother to the ever-popular 6R80 transmission began it’s use in consumer vehicles in the 2011 model year. It could be found in any of the Super Duty pickup trucks, gas, diesel, cab & chassis, etc. As a successor to the 5R110 Transmission, whose Drivetrain 101 can be found by clicking here, it was expected to provide a host of benefits over it’s predecessor.
Largely in the name of fuel economy, and for the demands of increasingly heavier duty work, the unit added one gear over its predecessor, making it a 6 Speed. This was a long time coming as Ford was the last of the “big 3” to implement a 6 Speed transmission into its heavy duty diesel truck lineup.
The tenure of the 6R140 ended with the recent advent of a 10 Speed automatic named the 10R140. Said unit arrived for the 2020 model year, ending a near decade reign of the 6R140 as Ford’s premier heavy duty 6 Speed automatic. In our years of perfecting these units, we’ve amassed a tremendous amount of data, facts and knowledge which we will proceed to share. Hence, we will now be observing the problems, and solutions, available to resolve and enhance all aspects of the 6R140 Transmission!
How the 6R140 Clutch Packs Work:
As a “clutch to clutch” style transmission, the 6R140 does not employee any servos, bands, levers or otherwise to control the application of any gears housed within the unit. Ford has been using clutch to clutch transmission assemblies on their larger trucks since the retirement of the historic 4R100 Transmission.
All vehicles that used this transmission had a PCM or TCM controlling the activation and deactivation pressure solenoids inside the transmission. This makes the 6R140 ineligible for a “Full Manual Valve Body” configuration or anything similar.
Problem #1 - The Torque Converter
Much like the Aisin Seiki torque converter, this transmission’s torque converter locks up facing the stator; not the flexplate. This is backwards of most automatic transmissions, and generally does one well in the area of heat management, torque capacity and longevity. Unfortunately, it is simply insufficient to withstand anything above factory power levels.
Once one expands beyond the factory horsepower and torque figures, the lockup assembly simply cannot suffice, you immediately have more truck than transmission. The factory converter features one flimsy friction plate that very quickly overheats when trying to enter a locked status in something like a tuned truck, or one running significantly larger tires without a regear.
Less observed is the issues of the factory stator. They don’t often break, but that isn’t the problem in the first place. Their stall speed is uncomfortably high, a beckoning to Ford’s submission to the EPA. The intent behind this was to ensure low idling emissions in drive, benefiting city fuel economy by a negligible margin.
The problem is that it robs the truck of a massive portion of its power in lower gears, and significantly increases the burden of heat on the transmission. Our 6R140 Torque Converters all feature a 100% custom stator ranging across all realistic stall speeds. If you have questions about the stall speed most befitting your application, call in and speak to an expert!
Problem #2 - The Input Shaft
In most transmissions, the input shaft is the most likely shaft to fail because it is the first to receive unbridled torque from the motor. Ironically, it is the second most in this transmission, but more on that later. The factory input shaft is physically very long but only about as wide as an L5P Allison input shaft. What does this mean? It can yield or physically fail in applications with higher power.
Moreover, the hub with which it attaches will often snap as well. It tends to crack right where the splines opposite the torque converter end (turbine splines) of the input shaft insert into it. This generally causes a low like pressure code putting the truck into limp mode.
Cryogenic treatment of these components is ample protection for unruly applications, and for most customers, this shaft is unlikely to break. It is simply worth understanding the problems that have been documented as applied to this component!
Problem #3 - The Intermediate Shaft
Taking the cake for most probable shaft failure, the intermediate shaft in this unit tends to die easily in aggressively tuned or highly empowered applications. This is because the intermediate shaft is now synchronizing in speed with the input shaft very rapidly against the mass of the truck as the 4-5-6 clutches apply. This rapid synchronization can cause it to snap.
Often, the torque converter’s controlled slippage prevents this concern. Other times, a wonton TCM tune or substantially more powerful truck will force this component to fail quickly. It is common that high performance applications will upgrade this to a 300M billet steel material; preventing failure at virtually any power level.
Problem #4 - The High Pressure Oil Pump
This transmission was the first where Ford began using the pump to house large portions of the valvetrain. As a result, it is susceptible to more crossleakage than the usual pump. We have studied this and determined that poor oil filtration and regularly high oil temperatures will accelerate this issue more than anything.
Further, we have discovered the pump gears will revert oil pressure at high mileage. The safest thing one can do is purchase a new OEM pump, then apply the appropriate modifications to said brand new pump. Remanufacturing these pumps is not safely possible as there isn’t enough room to upsize the valves without making portions of the casting critically thin.
Products such as our 6R140 Formula One High Pressure Oil Pump, standard across our entire 6R140 transmission lineup, resolve all of the aforementioned inferiorities by offering all of these solutions in one unit. Our unique oil pump allows the 6R140 to sustain massive line pressure numbers fluently and reach them quickly. The OEM high pressure oil pump simply does not have this to offer, hence its contribution to low quality shifts and lockup behavior.
Problem #5 - The Valve Body
As a valve body derived from the ZF Transmission manufactured ZF6HP26, the 6R140 valve body has a similar host of attributes and failure points as that specific transmission. Though not the "worst" on the market, it is certainly prone to a variety of common failures that have overwhelmingly lacked support from the aftermarket before Next Gen.
Firstly, the TCC Apply Boost Valve found inside the valve body is made of a low grade aluminum, and eats the valve bore at an accelerated rate. This contributes to the frequent issue of converter failure seen in deleted trucks, trucks with larger tires, heavier trim trucks such as Platinum or Limited models as well as other aggravating factors.
Think of this oil circuit as a balloon, and when it leaks oil out of it via the boost valve, it is like leaking air. You lose pressure inside the system, this pressure is critical because it applies a piston that engages the converter clutch pack. Less oil pressure means less torque capability in lockup.
Additionally, there are multiple different "dead" solenoids in this unit that serve more as seals than functional units, similar to the 5R110 transmission. Much like the 5R110 transmission, these can be replaced with end plugs and O-Rings to negate concern of crossleakage from this sensitive area.
Our 6R140 Valve Bodies are all manufactured with a complete OEM set of solenoids, all useless leak points replaced with O-Ringed end plugs, a recalibrated accumulation system, a sleeved TCC boost valve, laser cut separator plate and more. The reason we do not manufacture them any other way is simply because all of these factors contribute to the transmissions success. None of them should be forfeited in your rebuild.
Problem #6 - Direct/Intermediate Clutch Pack
Named interchangeably direct or intermediate, this clutch pack resides on the intermediate shaft of the 6R140 transmission. It is frequently found burnt due to inadequate clutch volume and inadequate paper quality. From the factory, the OEM uses 5 clutches in this clutch pack. Converting to an upgraded clutch material will enable a considerable amount of added power, as well as adding clutches to the clutch pack itself.
Unfortunately, the OEM offers neither, leaving the clutch pack a probable failure point in this transmission. This clutch pack also faces an undue burden in the sense that the computer often applies 4th gear rather rough, especially when in tow/haul mode. This is the equivalent of jamming your brakes rather than coming to a slow stop for this clutch pack.
Problem #7 - The Overdrive Clutch Pack
Perhaps more prolific than even failure of the direct and intermediate clutches, is failure of the Overdrive system in the 6R140 transmission. The factory only offers 7 clutches in this clutch pack, clearly thinking that is sufficient for heavy duty applications. Unfortunately, that is just not the case.
Although the solution for this clutch pack varies, we don't offer any complete units with a factory overdrive setup for the 6R140 transmission. It would be generally irresponsible as most consumers, even with stock power, can burn these clutches under the right conditions.
Much like the Direct/Intermediate clutch pack, the solution is a blend of upgraded clutch materials and more clutches altogether. Again, the OEM is seeking to create a cost effective product to bring to the masses. It is not rational to expect the OEM to use premium grade clutch materials, or to add in excess of what is necessary to support a "bone-stock" truck. As a result, many late model Ford Super Duty owners find themselves looking for a transmission early in it's life.
Problem #8 - The OEM Oil Pan
When this transmission was originally marketed to the masses, it was made for gas applications first, then diesel. Most gas vehicles have some level of concern for ground clearance when designing oil pans for longitudinally mounted automatics such as the 6R140 transmission. Further, it is very expensive to redesign something like an oil pan once one design has been affirmed.
The product of this is that the diesel 6R140 oil pan is the virtually identical to the gas 6R140 oil pan. Why does this matter? It has generally low oil volumes compared to almost any aftermarket pan, contributing to higher sustained temperatures across its life and consequentially, lessened clutch longevity.
Simply worded, the pan was designed to cut cost and time, not maximize cooling efforts to your 6R140 transmission. Because of this, all Next Gen Drivetrain 6R140's are manufactured with a deep oil pan. Maintaining comfortable temperatures inside this transmission is 100% necessary for those seeking a long-term transmission.
Problem #9 - The OEM Electronics
As mentioned in bullet-point #5, the OEM solenoids can be problematic. To expound upon this, the factory valve body is almost entirely controlled by solenoids that have a limited lifespan. A common problem with them is that as crossleakage in the valve body proliferates, it applies more stress to the solenoids by forcing them to engage or disengage at conflicting times.
Any rebuild that does not replace all of the electronics of the transmission, including the speed sensors and wiring harness, is simply incomplete. The OEM has updated some of these over time and replaced them with successive part numbers, and it is important to have the most current parts in your 6R140 transmission in the interest of longevity. Electronics are no exception.
One of the most popular transmissions on the market, the Ford 6R140 is tenured and capable, but not perfect. As these transmissions age and begin to exhibit symptoms of impending failure, it is important to understand what to look for, how to prevent it, and what transmission is appropriate for your personal needs. The 6R140 has all the ability to be an excellent transmission once built, and it's shortcomings are a loss of hope. If you help with a 6R140 transmission, call in and speak with one of our experts!