Other Articles - November - 2022

Problems and Fixes! Revisiting the 6R140 Transmission

The 6R140 transmission has been around since 2011. Throughout its reign as the heavy-duty transmission of choice for Ford, it was found primarily behind the F250, F350, F450, and F550 series trucks. The heavy-duty components made this unit extremely durable and reliable. However, this unit was not without problems of its own. So let’s look at some common issues and fixes for this unit!


One of the most significant concerns for this unit is its massive size. This transmission is not the most friendly unit to handle on a tear-down bench or in the building room. With the input assembly weighing in at a hefty 75 pounds and the overall unit weighing 350 pounds (dry, without the torque converter), great care and planning are needed before attacking this unit. Our ATRA rebuild book recommends using an engine hoist to disassemble and assemble this transmission. If you have not built one of these transmissions yet, please consider this before attacking this!

Once you move beyond fighting the weight of the beast, there is nothing tricky about successfully building this unit. However, one main concern is clutch pack clearance. Unfortunately, the original factory reference material gave incorrect clutch clearance information. We verified clutch clearances observed in good working units through research and used these as references (figure 1). Since this is a clutch-to-clutch shifting unit, it is important to set the clutch clearances within the specified ranges.


There are a few items to watch for inside this transmission. Some can be caught during the diagnostic process and may be repaired without removing the transmission. Since we have patterned failures and fixes, we will gladly share them!

Speed sensor and IMS codes are common with this unit. However, they can be operating temperature related or intermittent and difficult to duplicate. A common area of concern is the internal wiring harness. Splices within the harness assembly can become compromised and fail, causing intermittent circuit continuity issues (figure 2). Knowing what to look for allows you to clean and repair the existing harness using solder and oil-resistant shrink wrap for a permanent, predictable repair. Keep in mind the new OEM harness has splices like the original. So, inspect the harness thoroughly and repair or replace it as necessary.

The valve body is prone to collecting debris, especially with a high mileage unit that has not been serviced. Natural wear that produces friction, dirt, and fine metal is considered normal for this unit, but it can cause issues with the valve body’s operation.

One complaint related to debris in the valve body is neutralizing coming to a stop or harsh 5-4 and 6-4 forced downshift. Debris from normal wear and tear dropping into valve control channels causes the 1-2-3-4 control valve to stick (figure 3). Gear ratio DTCs or other performance codes may be stored in the PCM. In both cases, there may be no evidence of internal transmission damage. In most cases, you can make a target repair. Either replace the valve body or repair the related valve and/or bore damage.


Before chasing an overheating problem down, determine if the vehicle has a tuner installed. Diesel trucks are prone to have altered computer control programming that allows the engine to produce more torque and horsepower than initially designed by the manufacturer. On top of adding horsepower, lock-up is often delayed to allow torque multiplication to give the vehicle more power to the wheels. Both scenarios generate more heat than normal. You must drive the vehicle to verify that the lock-up scheduling is adequate for keeping the transmission operating temperature within the correct range. I recommend returning the vehicle to factory programming levels for comparison and accurate diagnostic purposes.

I find one ‘fun fact’ about this transmission very surprising but significant. The normal operating temperature per manufacturer specifications for this unit is 195°F to 230°F! So, in warmer climates like Arizona in the summer, it is normal to have a unit operating consistently at 210-220°F with no codes and no issues. However, if the temperature climbs beyond this, this indicates a cooling problem.

Once you verify that you have stock-level programming and that lock-up is commanded and working correctly, there are two common areas to check:

  • The secondary cooling system.
  • The pump stator sleeve.

You want to start with the cooling system check since the transmission needs to be removed to check the pump stator sleeve. However, you would reverse this order if the unit is on the bench.

Diesel applications that use the 6R140 have dual cooling systems. Two separate systems have independent reservoirs to manage cooling for different components. The primary cooling system cools the engine only. The secondary cooling system is dedicated to cooling the following components:

  • Transmission fluid warmer
  • Intercooler
  • Fuel Cooler
  • EGR Cooler

Out of all these components, the transmission generates the most heat. Therefore, if the reservoir for the secondary cooling system is low, the transmission will overheat. Inspect all the listed components for external or internal leaks. Also, verify that the secondary coolant pump is operating correctly. Another area of concern is the pump stator area. You will need to remove the stator from the body to inspect the pump body sleeve. It can partially turn, blocking off the converter charge oil (figure 4). The converter charge oil feeds the cooling system, so a restriction causes overheating. Replace or repair as necessary.


Another common issue for this transmission is a no-move complaint after the rebuild. It may even be a complaint with the vehicle coming in the door. Upon disassembly inspection, the problem may not seem obvious. However, a closer inspection usually reveals an obvious fault. The input shaft is spin-welded to the 4-5-6 drum. The weld can completely break free from the drum, but will be held together by the return spring, piston, and snap ring (figure 5).

In some cases, the drum will air-check well. However, when you grab the shaft, you can turn it while holding the drum. Then, use transmission fluid or solvent on the gear side of the drum, air-check the assembled clutch pack and observe for leaks.

The 6R140 transmission is a unit that has not been popular in most aftermarket shops. However, they are showing up in need of diagnosis and repair. Knowing patterned failures and fixes helps us quickly get these vehicles in and out of the shop. ATRA is dedicated to giving you fixes as we find them so you can keep your customers on the road!