Ford Workshop Service and Repair Manuals

In principle, the transaxle comprises two independent gear trains.

During driving, one gear train is always positively connected and the next gear is already engaged in the other gear train (although the clutch for this gear is still open).

Design of the transaxle

The name 6DCT450 stands for:

• 6 = Six gears
• D = Dual
• C = Clutch
• T = Transaxle
• 450 = Torque

The transaxle is regarded as a further development of the automated manual transaxle (AMT), for example the iB5 and MT-75.

Ford is installing the transaxle for the first time in the Focus (C307), model year 2008.5 (02/2008-) with 2.0L Duratorq-TDCi (DW) diesel engine. It will be used universally in further vehicle lines.

The transaxle operates without interruption of the propulsive force, a main disadvantage of automated manual transaxles. Even compared with the most modern automatic transmission, its higher efficiency is clearly noticeable.

Fuel savings of 4-8 % are possible with the transaxle.

The first time a dual-clutch transaxle was used was in the 80s in motor racing. The high computational complexity required in the control system for a smooth overlapping gearshift, however, meant it never made it into large-scale production.

The requirement profile for the transaxle has been designed for "comfort" and "functionality".

As with conventional manual transaxles, the gear ratios are accommodated inside a direct manual transaxle in the form of gear pairs on input and output shafts.

In contrast to conventional manual transaxles, the input shaft is in two parts.

The input shaft comprises an outer hollow shaft that connects gears 2, 4 and 6 with the one clutch as well as a core shaft that connects gears 1, 3, 5 and reverse gear with the other clutch.

The plate assemblies of the “wet-running” (in fluid) clutches, which in this transaxle are electronically controlled and hydraulically actuated, can be packed space-savingly into each other so that they can also be used in transverse-mounted engines.

The external gearshift mechanism has been carried over from the CFT 23 automatic transaxle (Focus 2004.75 (07/2004-) and C-MAX 2003.75 (06/2003-)).

The selector lever has the following functions:

• P - Park position
• R - Reverse position
• N - Neutral position
• D - Electronic control of the transmission ratio using the TCM (Transmission Control Module)
• M - Manual shifting using a +/- function

If the selector lever is in the "P" position and the vehicle has been switched off, second gear and reverse gear will be engaged via the TCM.

This results in a faster response after the starting process.

Special features of the transmission include:

• 6 gears plus reverse gear
• Front transverse installation
• All-wheel drive (AWD) option
• Hybrid option
• Parallel wet clutch
• Internal electronic gearshift mechanism
• Intelligent gear change control

Technical Data

Description of the dual-clutch system

The illustration shows a cutaway view of the multi-plate clutch

The transaxle in the dual-clutch system has two clutches.

The advantage of this is that two gears can always be engaged at the same time. One of the clutches operates the uneven gears, the other clutch the even gears.

The dual-clutch system for the transaxle application has been developed by the company BorgWarner. It features an upstream, wet-running torsional vibration damper that reduces the vibrations coming from the engine (unevenness in rotation).

The engine's torque is introduced into the drive-side primary element (flange) of the torsional vibration damper by means of the crankshaft via dog teeth. The drive-side secondary element (damper shells) is connected with the input housing of the dual clutch.

The torque at the engine-side shell is transmitted from the shells of the torsional vibration damper into the clutch input housing, onwards into the main hub and finally to the inner plate carrier.

Apart from functioning as a mounting, the clutch support also contains the oil passages. They supply the clutch with pressurised oil for clutch actuation as well as with cooling oil for dissipating the frictional energy during clutch actuation.

When the clutch plunger is pressed, the engine torque is transmitted via the respective plate assembly comprising steel plates with internal teeth and friction plates with external teeth to the engine- or transaxle-side outer plate carrier and thus to the hollow or core shaft of the transaxle.

The associated clutch is actuated as a function of the gear request from the transmission control module. Pressure is applied to clutch 1 for gears 1, 3, 5 and R and to clutch 2 for gears 2, 4 and 6. The gearshift mechanisms of the two clutches overlap during gearshifting, which permits acceleration with nearly no interruption of the propulsive force.

Operating principle of the transaxle

With the dual-clutch transaxle, two gears (ratios) are engaged at the same time through the use of a dual multi-plate clutch in combination with electro-hydraulic control.

One of the multi-plate clutches is engaged in driving mode, the other is already preselected when approaching the next gearshift with the clutch open.

The clutch of the previously activated gear opens according to the accelerator pedal position and request by the driver and simultaneously closes the other clutch in order to engage the preselected gear.

The illustration shows the gearshift process in a manual transaxle

The illustration shows that in conventional manual transaxles, gearshifts result in a customary interruption of the propulsive force.

The illustration shows the gearshift process in a 6DCT450 transaxle

With this gearshift, shown under load in the illustration, the power flow is only slightly restricted; there is constant propulsion perceptible.

Torque path

NOTE:When looking at the illustrations, please note that the torque flows from the input shaft once via the core shaft and once via the hollow shaft.

1st gear

The torque is introduced into the dual clutch via the clutch claw. From there, the power is transmitted via clutch 1 to the input shaft (core shaft). The input shaft transmits the torque to the first gear of the output shaft (1st to 4th gear). The torque is transmitted to the differential via the output pinion.

2nd gear

The torque is introduced into the dual clutch via the clutch claw. From there, the power is transmitted via clutch 2 to the input shaft (hollow shaft). The input shaft transmits the torque to the second gear of the output shaft (1st to 4th gear). The torque is transmitted to the differential via the output pinion.

3rd gear

The torque is introduced into the dual clutch via the clutch claw. From there, the power is transmitted via clutch 1 to the input shaft (core shaft). The input shaft transmits the torque to the third gear of the output shaft (1st to 4th gear). The torque is transmitted to the differential via the output pinion.

4. gear

The torque is introduced into the dual clutch via the clutch claw. From there, the power is transmitted via clutch 2 to the input shaft (hollow shaft). The input shaft transmits the torque to the fourth gear of the output shaft (1st to 4th gear). The torque is transmitted to the differential via the output pinion.

5th gear

The torque is introduced into the dual clutch via the clutch claw. From there, the power is transmitted via clutch 1 to the input shaft (core shaft). The input shaft transmits the torque to the fifth gear of the output shaft (5th, 6th and reverse gear). The torque is transmitted to the differential via the output pinion.

6. gear

The torque is introduced into the dual clutch via the clutch claw. From there, the power is transmitted via clutch 2 to the input shaft (hollow shaft). The input shaft transmits the torque to the sixth gear of the output shaft (5th, 6th and reverse gear). The torque is transmitted to the differential via the output pinion.

Reverse gear

The torque is introduced into the dual clutch via the clutch claw. From there, the power is transmitted via clutch 1 to the input shaft (core shaft). The input shaft now transmits the torque to the reverse gear of the output shaft (5th, 6th and reverse gear). A reverse idler gear ensures reversal of the direction of rotation. The torque is transmitted to the differential via the output pinion.

Parking lock

The illustration shows the parking lock

There is a parking lock integrated in the second output shaft for safe parking of the vehicle and to prevent it from rolling away when the parking brake is not applied.

A parking lock needs to be installed since the fluid pump is not actuated when the engine is switched off. The absence of fluid pressure in the transaxle means that both clutches are open.

Engagement of the lock pawl (4) takes place exclusively by mechanical means. A gearshift cable actuates the shift unit (1) installed at the transaxle via the selector lever.

The parking lock is engaged by the movement of the selector lever into the "P" position. This causes the lock pawl (4) to engage in a tooth gap of the lock wheel (5).

When the lock pawl (4) makes contact with a tooth of the lock wheel (5), a compression spring (3) at the rod is tensioned. When the vehicle moves, the relaxing of the compression spring (3) causes the lock pawl (4) to engage in the next tooth gap in the lock wheel (5).

Synchronisation

The synchronizers used in the transaxle feature a carbon coating.

Gears 1, 2, and 3 and reverse gear have double synchronizers. A major advantage of double synchronizers is their significantly enlarged friction surface. The effective surface area is increased by approx. 100%.

Gears 4, 5 and 6 have single synchronizers.

Fluid pump/filter unit

The illustration shows the installation position on the transaxle

The transaxle has a separate fluid circuit for all transaxle functions.

This fluid circuit needs to meet the following requirements:

• Consistent viscosity over the entire temperature range
• Resistant to mechanical stresses
• Ensures hydraulic control
• Ensures clutch pressure control

The illustration shows the fluid pump with suction fluid filter

The fluid pump is designed to deliver sufficient fluid pressure as well as a large enough quantity of fluid at every operating point.

The fluid pump used in the transaxle is an external gear pump with a constant delivery volume.

The pump comprises an aluminium housing with cover, whereby the gears are introduced into the housing.

The volume of fluid trapped in a tooth gap is delivered from the intake side to the delivery side through the rotation of the gears. A main pressure regulator distributes the fluid in the timing case, whereby excess fluid is routed back into the fluid pump.

The illustration shows the filter unit

The hydraulic function of the filter system consists of ensuring that contamination by non-soluble particles in the transmission fluid does not exceed a maximum permissible level.

The filter system also assumes the function of the feed and return to the transaxle cooling system.

The fluid to be cleaned is delivered by pump via the suction fluid filter to the hydraulic system to be supplied. The fluid delivered by the pump is divided into two fluid flows in the hydraulic system.

The fluid flow is routed into the respective hydraulic channel of the pressure filter system as a function of the fluid temperature:

• The cold fluid flow is routed directly to the pressure filter installation space.
• The warm fluid flow is routed to the pressure filter system, from there discharged via the connection to the radiator feed and after the radiator system, recirculated via the radiator return. This cooled fluid flow is then routed into the pressure filter installation space.

The fluid flows via the pressure filter element back into the transaxle's fluid pan.

The pressure loss in the filter must not exceed 1.0 +/- 0.2 bar. If this value is exceeded due to contamination, a bypass valve is opened and the flow no longer passes through the filter.

Electronic sensor and control unitTCM (transmission control module)

The TCM is used to actuate and control the transmission. The transaxle comprises two input shafts, each of which are switched on and off by a clutch. This permits operation with minimal interruption of the propulsive force during the shifting process. The TCM performs the following tasks:

• Actuating the clutches with measurement of the clutch pressure
• Actuating four gear selectors with measurement of the travel
• Actuating two safety valves, one for the core shaft and one for the hollow shaft
• Actuating the main pressure
• Actuating the cooling oil pressure
• Measuring the clutch speeds
• Measuring the transaxle temperature

Transmission fluid flows all the way around this unit.

This results in a smooth shifting process with almost no interruption of the power transmission.

The TCM:

• processes the sensor signals,
• measures the engine speed, velocity and transaxle load,
• detects the position of the mechanical components,
• electromagnetically controls the valves and sliders of the hydraulic transaxle mechanism.

The TCM learns (adapts) the positions of the clutches, the positions of the gear selectors when the gear is engaged and the system pressure.

The selector fork unit is adjusted by routing fluid into a cylinder via the hydraulic module, which produces a linear movement in the piston attached to a selector fork.

Since the opposing cylinder is depressurised, the selector fork unit is moved.

This results in the gear being engaged via the sliding sleeve (synchronizer assembly).

As soon as the gear is engaged, the cylinder is no longer pressurised.

The engaged gear is now maintained by the relief of the shift teeth and the selector fork.

The illustration shows the shift detent

The non-engaged gears are held in neutral position via interlocking of the selector forks (see illustration E98927).

The illustration shows the permanent magnets at the selector fork unit

Each selector fork unit has a permanent magnet. A distance sensor detects the current position of the selector fork by means of these magnets. The position of the selector fork can, in turn, be used to determine the engaged gear.

TR (transmission range) sensor

The illustration shows the installation position of the sensor

The TR sensor is integrated in the transmission housing.

The TR sensor detects the selector lever position selected by the driver and forwards this information to the TCM.

It is not necessary for it to learn this electronically via the IDS (Integrated Diagnostic System).

Transaxle input speed sensor

The illustration shows the installation position of the sensor

The sensor scans the outside of the dual clutch electronically and senses the transaxle input speed.

The sensed signal serves as a variable for calculating the slip of the multi-plate clutches.

Function of the gearshift control system

The gearshift control system is based on a software strategy for gearshift point determination which corresponds to the driving conditions and the driver input.

The TCM actuates the relevant solenoid valves in order to perform an automatic gearshift.

All parameters (e.g. vehicle speed, accelerator pedal angle, signal from the brake pressure sensor or the ESP inclination sensor) are processed by the TCM.

Adaptive control

The TCM monitors each gearshift in order to enable smooth gearshifting under all driving conditions. This is achieved by the control module reducing or increasing the hydraulic system pressure (clutch and selector fork actuation) for gearshifting.

The following are adapted:

• the clutch charge,
• the clutch pressure point,
• the clutch torque relative to the clutch pressure (synchronisation of the engine torque and transaxle torque),
• the position of the selector forks.

The modified pressure and position values are stored in the non-volatile RAM (random access memory) of the control unit. This permits improved shifting smoothness and increases transaxle service life.

Gearshift control

Automatic mode, selector lever in "D" position

• The TCM adapts the shift points to match the driving conditions.
• If special driving conditions are detected, the TCM switches to predefined characteristics.

Manual mode, selector lever in the manual shift gate

• If the vehicle speed decreases so that the engine speed falls below the lower limit, the TCM causes the transmission to shift to a lower gear.
• If the driver attempts to shift to a lower gear and there is a danger that the engine speed would exceed the upper limit, the TCM prevents the gearshift.
• If an engine speed of 4,500 rpm is exceeded during acceleration, the system automatically shifts to the next highest gear.
• Kick-down gearshifts are also executed in manual mode.
• Strategic starting in 2nd gear is possible (replacement for winter mode).

NOTE:Manual gearshifting can only be performed if the engine speeds do not exceed or fall below predetermined values.

Selector lever from "N" to "R" position

• The TCM only permits shifting to reverse gear if the vehicle speed is less than 12 km/h.
• If the vehicle speed is greater than 12 km/h, reverse gear is not engaged and the gearshift is thus prevented.

Special driving conditions

Uphill driving

• The TCM detects uphill driving by comparing the engine torques transmitted by the PCM (powertrain control module) with the stored torques valid for driving on a level road.
• If the engine torque in the driving situation is higher, the TCM detects uphill driving and executes a shift to a lower gear to increase the tractive force.

Downhill driving

• The TCM detects downhill driving by comparing the engine torques transmitted by the PCM with the stored torques valid for driving on a level road.
• If the engine torque in the driving situation is lower, the TCM detects downhill driving and executes a shift to a lower gear to reduce the load on the vehicle brakes.

Altitude correction

• Engine performance is reduced as air pressure decreases at higher altitudes. This situation is detected by the PCM and transmitted to the TCM.
• In order to compensate for this operating situation, the TCM changes the shift points and adapts the starting characteristics.

Speed control system.

• When the vehicle speed control system is switched on, a gear change can be executed by the TCM.

Torque reduction in the "D" position with the brake depressed and the vehicle stationary

• If the vehicle is stopped in selector lever position "D", the TCM preselects 2nd and reverse gear and reduces the torque of the driveaway clutch to approx. 5 Nm.
• This function stabilises idling, lowers fuel consumption and reduces vibrations transmitted by the powertrain.

Rollback prevention function

• If the vehicle stops on an uphill incline, 1st gear is preselected in "P" and in "N" and, depending on the uphill gradient, the engine idle speed is increased from 800 to up to 1,100 rpm.
• If the vehicle stops on a downhill incline, reverse gear is preselected in "P" and in "N" and, depending on the downhill gradient, the engine idle speed is increased from 800 to up to 1,100 rpm.

Service and diagnostic information

visual inspection

A thorough visual inspection of the transaxle is necessary for successful diagnosis.

A visual inspection covers the following points:

• Plugs and connectors,
• Ease of movement of the selector lever,
• Selector lever position and selector lever position display
• Fluid leakage
• Fluid level check,
• Modification/retrofitting
• Mechanical damage to the transaxle.

When inspecting connectors, remember that the plugs may only be disconnected when they are not energised.

The transaxle electronics may be destroyed by static charge. To prevent damage, the technician must take appropriate protective measures.

NOTE:The exact descriptions of these protective measures can be found in FordEtis.

Self-test and diagnosis

The TCM monitors all of the transmission sensors and communicates with many electronic vehicle components including the PCM. If a fault occurs, the driver is informed via a warning indicator and a text message in the instrument cluster.

Faults are stored as diagnostic trouble codes in the fault memory of the TCM and can be read out and if necessary cleared using the IDS.

Limp home mode

The TCM software contains functions which take control of the transmission if serious faults occur.

The fault characteristic decides which strategies are to be used.

The vehicle remains capable of restricted operation, unless there is a fault in the TCM itself or at the TR sensor.

NOTE:If the TCM or the TR sensor is defective, both clutches open and it is no longer possible to continue driving.

Different measures are implemented depending on the current gear position and driving situation when the fault occurs:

• When a fault occurs, the TCM makes it possible for the vehicle to maintain restricted operation. The distance travelled should be kept as short as possible and extreme driving manoeuvres (e.g. overtaking manoeuvres) should be avoided for safety reasons.
• In limp home mode, a text message is displayed in the instrument cluster and/or the MIL (malfunction indicator lamp) and/or the transmission warning light comes on (depending on the fault type).

When the engine is restarted (ignition key removed for approx. 15 seconds), the transaxle is no longer in limp home mode.

There is no longer a fault indication on the instrument cluster, and the MIL is off. However, the fault remains stored in the TCM. If the fault is still present, limp home mode is reactivated.

Limp home strategy

Different limp home programs are activated depending on the fault and driving situation (59 different programs defined as of October 2007).

The fault responses range from blocking individual gears through blocking an entire transaxle path (even/uneven gears) to driving in only the gear already engaged.

All transmission ranges (“R” and “D”) or the manual shift gate are available in principle, provided they have not already been restricted by the fault that occurred.

In the event of a fault, it is recommended to continue driving so long as it is necessary and to look for the nearest workshop or to park the vehicle in a safe location.

If the vehicle has already come to a stop and it is not possible to continue driving, restarting (removing the ignition key for approx. 15 seconds) may clear the fault and enable the driver to continue driving to the workshop in the event of an emergency.

Oil temperature

If the fluid temperature in the transaxle is too high, specific measures will be initiated depending on the temperature.

The calculated temperature of the clutch and the transmission fluid sump temperature are considered.

Clutch temperature increases above:

• 160°C – warning level 1: The transaxle warning indicator in the instrument cluster lights up yellow, oscillations in the clutch torque cause vibrations in the vehicle. The driver is thus prompted to press the brake and by so doing allow the clutch to open and cool down.
• 165°C – warning level 2: As for warning level 1, but with more severe oscillation.
• 170°C – warning level 3: The clutches are opened to avoid damaging them.

Transmission fluid temperature increases above:

• 125°C – warning level 1: The transaxle warning indicator in the instrument cluster lights up yellow, oscillations in the clutch torque do not cause vibrations in the vehicle.
• 136°C – warning level 2: As for warning level 1, but with more severe oscillation.
• 138°C – warning level 3: The clutches are opened to avoid damaging them.

The vehicle can be operated once more without restriction after the cooling down stage.

To permit rapid cooling down and to ensure continuous lubrication of all components, the engine should run and not be switched off.

Transmission fluid level check

NOTE:It must be ensured that the transaxle is not working in limp home mode or that there are no diagnostic trouble codes.

The transmission fluid level depends on the fluid temperature!

• Checking the fluid level when the temperature is too low will result in overfilling.
• Checking the fluid level when the temperature is too high will result in underfilling.

NOTE:This instruction must be followed point for point to guarantee a proper fluid level check.

The reason is a multi-chamber fluid system that requires a higher fluid level for the electromechanical control unit than in the rest of the transaxle.

The fluid that escapes directly after the fluid level check hole is opened is not an indication of a correct or even excessive fluid level.

In any case, fluid must be added through the filler opening with the fluid level check hole open until the fluid runs out at the fluid level check hole.

In order for the transaxle to function properly, it is vital that the transmission fluid level is correct.

• Follow the statutory environmental provisions.
• The engine must not be started if the fluid level is incorrect.

Transporting/towing the vehicle

As the transmission is not sufficiently lubricated during towing, the following must be remembered:

• the selector lever must be in the N position,
• the maximum towing speed must not exceed 30 km/h,
• The maximum towing distance must not exceed 50 km
• the vehicle may only be towed at temperatures above 0°C.

The vehicle may only be towed in the direction of travel.

Rolling or overrun operation when the engine is stopped

Failure to elevate the drive wheels, decouple the powertrain or remove the halfshafts before starting rolling or overrun operation may cause damage to the transaxle.