Delivering the Goods - November - 2022

The D7GF1 and D7UF1 – A Closer Look at Hyundai/Kia DCTs

Dual-clutch transmissions have become more prevalent in a quest to improve car fuel efficiency. The absence of a torque converter and an engine-driven oil pump significantly reduces horsepower consumption. Also, adding a direct mechanical transfer of torque through gears produces the most efficient throughput of any transmission. Because of these attributes, they have found a home behind low torque and low horsepower engines. Hyundai and Kia capitalized on the advantages of dual-clutch transmissions with their 7-speed applications, which have been in production for over ten years. Recently, these vehicles have been showing up at more aftermarket shops with concerns. So, let’s familiarize ourselves with these transmissions so we can confidently approach them!

A UNIT OVERVIEW

The D7GF1 and D7UF1 are 7-speed, dual-clutch (DCT), automatically shifted manual transmissions manufactured by Hyundai Powertech, the powertrain division of Hyundai Motors. The D7GF1 unit is behind the smallest, low-torque engines, while the D7UF1 handles higher torque output motors (figures 1 and 2). Note that these units have considerable internal ratio differences based on application.

The DCT allows sequential gears to be pre-shifted while operating in another range. It uses electric servos and motors as actuators to control clutch operation and transmission shifting. A stand-alone TCM sends signals to actuators on the transmission. Power is transferred from the engine through a dry dual-clutch assembly coupled to a dual-mass flywheel.

THE COMPONENTS

Unlike other DCTs, the Hyundai/ Kia units use electric servos, motors, and solenoids to control gear shifting and clutch operation. A Clutch Actuator and Gear Actuator control all necessary functions to operate the transmission. Both actuators are serviceable without removing the transmission.

The Clutch Actuator has two electric servos with position sensors built into them. The TCM commands the servos to operate the clutch to launch the vehicle and shift. The Gear Actuator has two shift motors, two select solenoids, and four sensors to monitor each component. In addition, two input speed sensors provide TCM feedback for precise clutch actuation and shifting. The unit is also equipped with an inhibitor switch. All actuators and sensors are serviceable without removing the transmission.

The 7-speed DCTs use a dual-mass flywheel. Inspecting the flywheel when the unit is removed is crucial to service the clutch assembly. Check the flywheel for excessive lateral movement, damaged or broken dampener springs, and worn drive teeth. A failing flywheel can cause vibrations and rattling or banging noises.

A stand-alone TCM controls vehicle launch and shift timing by commanding the actuators according to driver input and vehicle sensor feedback. The TCM uses inputs from the driver, ECU, Skid Control Unit, and other sensors to determine clutch actuation and gear selection.

GEAR ACTUATOR ASSEMBLY

The TCM controls gear selection by operating the Gear Actuator assembly. The actuator consists of two motors and two solenoids that engage internal linkage in the transmission to shift separate shift rails (figure 3) independently. One motor and solenoid shift the odd gear rail while the other set shifts the even gear rail. The mechanically selected range is verified by a sensor located at each motor and solenoid in the assembly.

While the shift motors are identical, the connectors are unique, so you cannot swap the motors for testing purposes. The Gear Actuator assembly is sold as a component. The individual motors, sensors, or solenoids are not available from the dealer separately as of now.

CLUTCH ACTUATOR ASSEMBLY

The Clutch Actuator Assembly is an electromechanical device that operates the dual clutch assembly. Two electric servos operate individual clutch forks attached to throw-out bearings. The clutch forks apply and release the clutches. The electric servos receive commands from the TCM, timing the application and release of the clutches according to commanded gear selection.

The assembly is bolted to the transmission near the radiator. The actuator rods engage the clutch forks at the bell housing, while a detachable shroud covers the actuator rods and clutch fork opening. The Clutch Actuator assembly is designed to adjust mechanically to clutch wear automatically. As a result, the length of the individual rods shorten as the clutch wears.

SERVICING PROCEDURES

Like most dry dual-clutch units, the clutch will need to be replaced at some point in the vehicle’s lifetime. It will most likely be the service that brings it to your shop. Removing and installing the clutch assembly is very straightforward. Special tools are available for this but are not required. Clutch kits are available through aftermarket sources as well as the OEM.

After replacing a clutch, some essential procedures must be followed to finish the job correctly. The Clutch Actuator needs to be addressed based on the repairs performed as follows:

  1. If a new clutch assembly and a new Clutch Actuator were installed, perform the Clutch Relearn procedure. A new Clutch Actuator assembly comes adjusted to the ‘factory zero’ settings for a new clutch assembly.
  2. If a new clutch assembly was installed using the original Clutch Actuator, perform a ‘factory zero’ adjustment on the Clutch Actuator assembly, then complete the Clutch Relearn procedure.
  3. If only the Clutch Actuator was replaced, and the original clutch is used, measure the lengths of the apply servo rods and adjust the replacement Clutch Actuator rods to match those of the original. Then, perform the Clutch Relearn procedure.

CLUTCH ACTUATOR ADJUSTMENTS

The Clutch Actuator assembly is adjustable. Factory tools are available for this; however, not all are necessary. The goal for adjusting the actuator is to reset the rod lengths to factory zero settings or to match the lengths of the original actuator rods (when just replacing an old actuator).

A special tool to adjust the rods is recommended (figure 4). First, remove the Clutch Actuator from the transmission to measure and adjust the rods. Then, the special tool is inserted into a keyway in the body of the actuator for each servo. Rotate to lengthen or shorten as needed.

The special tool must be removed to measure the adjusted length.

If the Clutch Actuator assembly is replaced due to functional defects or other issues, measure the length of the rods (figure 5). Use a vernier caliper to measure from the actuator housing base to the end of the rod. Pull on the rod while making your measurement. Then, adjust the lengths of the rods (dimension A in figure 5) on the replacement assembly to match those measurements.

When replacing the dual-clutch assembly and using the original Clutch Actuator, you must reset the rod lengths (dimension A, figure 5) to the ‘factory zero’ settings. The “factory zero’ length for all 7-speed applications is 71.5 to 72.5 mm. Reference Kia technical bulletin TRA085 for details on the adjustment procedure.

CLUTCH LEARN PROCEDURE

Whenever replacing or adjusting the Clutch Actuator assembly, replacing the clutch assembly, or replacing the Gear Actuator assembly, the clutch relearn procedure must be performed. The process allows the TCM to determine the clutch touch points for vehicle launch control and shift timing purposes. The clutch learn procedure is achieved using a factory scan tool or equivalent. The scanner provides commands and instructions to be followed. To prepare the vehicle for the process, perform the following steps:

  • Ensure the vehicle ignition is ON (engine off) or HEV is not ready.
  • Vehicle must be in PARK.
  • No DTCs present.
  • Do not step on the brake.

Note that the learning function may be attempted only ONCE per ignition cycle! To make subsequent attempts, cycle the ignition OFF and then ON. The first stage of the learning function is static. It will take up to 60 seconds, then prompt you to start the vehicle or place HEV in a “ready” state:

  • Keep the vehicle in PARK.
  • Do not depress the brake or accelerator pedals.

After the static test completes, you will be prompted to start the vehicle for dynamic learning.

The dynamic learning procedure will take up to 60 seconds to complete. During this time, the computer will establish the clutch touch points by modulating the Clutch Actuators. You will feel bumps during this test. When finished, the scan tool will inform you that the procedure has been completed successfully and prompt you to turn the ignition off and wait for 30 seconds. During this time, the modules are writing learned data to the memory. Failure to allow ample ignition off time could result in lost or corrupted operating data! Afterward, restart the vehicle and drive to verify that proper launch and shift feel has been achieved.

The clutch learn procedure may fail to complete if the Clutch Actuator control rods are out of adjustment. In addition, faulty vehicle launch and/or poor shift quality may also occur if the adjustments are close enough for the clutch learn procedure to run to completion. In either case, remove and readjust the Clutch Actuator rods, then repeat the clutch learn procedure to correct these conditions.

DCT transmissions are here to stay. There will be variations on how the unit is controlled, clutch design, and computer strategies; however, the basic functions will be the same. ATRA is here to keep you in the know as these units begin to show up at shops so you can approach new technology with confidence, diagnose, repair, and deliver the goods!