The Dual Clutch DCT W6DGA Transmission

Getrag, the maker of several Powershift Dual Clutch transmissions both wet and dry, is beginning to show up for repairs outside of warranty. The most common of them is the wet clutch 6DCT470 in Mitsubishi’s Lancer EVO and Ralli-Art vehicles (Figure 1). Mitsubishi calls this its 6-speed W6DGA transmission, which it matched up with its 2.0L Turbo engine.

For those who have yet to be introduced to the basic operation of this style transmission, the double wet clutch arrangement is quite ingenious. Briefly, there are two input shafts (one inside the other) that spline to their own clutch drive hubs. The C1 clutch assembly, when fully applied, drives the odd gear drive hub for 1^st, 3^rd, 5^th and reverse gears. The C2 clutch assembly, when fully applied, drives the even gear hub for 2^nd, 4^th and 6^th. Both clutch housings are driven at engine speed.

The way in which these two input shafts mesh with their related output shafts allows for shift forks to preselect both an odd and even gear. For example, upon start up, first and second gear can be immediately selected. When a forward drive range is selected the odd gear clutch (C1) is commanded to be engaged. Once a shift into second is required, the odd gear clutch is released as the even gear clutch (C2) applies. As speed increases, the computer prepares for the next shift by disengaging

first gear engaging third. Once a second to third gear shift is needed, the C2 clutch releases and the C1 clutches apply. The shift can be very swift making it a perfect transmission for performance vehicles. In fact, a man named Adolphe Kégresse designed this concept back in the late-1930s. By the mid-1980s Audi and Porsche used this concept in their race vehicles. Today, Getrag calls its design of it as its Powershift Transmission.With these two clutch assemblies constantly applying and releasing, eventually they will need to be replaced and would be one reason why one may show up on your doorstep. If the drum assembly

needs to be removed, it would be best to place the transmission into neutral before pulling the transmission out of the car. A scan tool can verify a neutral state has been achieved by seeing a 0 mm reading for each fork (Figure 2). If this cannot be achieved, it will need to be done manually on the bench. This can be done by removing the spring loaded detent bolts (Figure 3) using their threaded holes as access points to center the shift rails in the neutral position. Having the synchronizer hubs in the neutral position makes it easier to remove the clutch drum assembly.To gain access to the drum assembly, three clutch cover tabs need to be removed (Figure 4). The

inner and outer diameter of the clutch cover is rubber bonded making it a bit of a challenge to remove it without damaging the cover. For this reason it has been referred to as a sacrificial cover. The manufacturer intends for it to be replaced but if the bonded rubber is still good, a little patience is all you need to walk it out of the housing and save yourself a few bucks. If the drum assembly is replaced with a new one from the dealer, it will include a new cover

Once the cover is removed (Figure 5), the clutch housing assembly comes into view. This assembly is held fast to the sealing ring tower via a spanner nut. This will require a special tool to unscrew it from the tower. As you look at the center of the clutch housing, there are four access holes (Figure 6). A long pick can be inserted into one of the holes to align the slots that are in the two internal clutch drive baskets so that a special tool can reach the spanner nut (Figure 7).

The unit shown in this article was shipped in from the Netherlands by Automatic Choice to the Alto Products location in Atmore, Ala. It was there where this unit was disassembled. At the time, this special tool was not available so Alto’s in-house tool and die department made one (Figure 8).

Once the tool was in place the spanner nut was loosened. It only takes about six or seven complete counterclockwise rotations to fully release the spanner nut from the ring tower (Figures 9, 10 and 11). With the unit being on its side, care will be needed to remove the housing assembly by giving it a slight lift for it to clear the sealing rings (Figure 12). Otherwise, the unit could be placed on to its back to release the spanner nut and lift the assembly out of the transmission.

If you are careful, this drum assembly can be disassembled to replace clutches and molded pistons. It is highly recommended to mark parts before disassembly to be used for alignment whenreassembling the housing to eliminate the possibility of vibrations.

The drive pump gear is part of the back cover (Figure 13). The inner diameter of this gear is a snap ring that holds the cover to the ring tower sleeve. This cover has enough flexibility to depress the cover without bending it. It needs to flex just enough to clear the snap ring from the integral pump drive gear (Figure 14). The assembly is then flipped around where the large selective L shaped snap ring holding the cover to the drive hub and damper assembly can be removed (Figure 15). The damper housing, C1 and C2 clutch drive baskets and the spanner nut can be separated from the back cover containing the two clutch assemblies (Figures 16 and 17). Alto Products developed

clutch and piston kits providing the means by which this assembly can be rebuilt. It is important to note that all friction plates have spiral type oil grooves making them direction sensitive (Figure 18). Pay attention to their direction upon disassembly. It is imperative that they be installed exactly the way they came out; otherwise shift quality will be affected.Getting ahead of myself, whether you rebuild the double clutch assembly or replace it with a new assembly, a “Tech In” process will need to be conducted using a capable scan tool. Bob Nuttall from Autotech sent in screen shots using in a Solus Ultra (14.4 version software) to get the job

done (Figures 19, 20 and 21). This critical procedure will ensure proper operation of the double clutch shift strategy.

After the work is completed with rebuilding the assembly or a new assembly was obtained, to install it properly requires a bit of finesse. Nuttall offers his experience on how he successfully installs the drum assembly.

He makes a tool using 1½-inch PVC pipe flange as a base. He inserts a 4-inch length piece of 1½-inch PVC pipe into the base and he then fastens a 1½-inch PVC pipe coupler over the pipe. The coupler needs to have a 2.41-inch O.D. and a 2.11-inch I.D. for this to work properly as this is the end that will go into the drum assembly and align the spanner nut (Figure 22).

He also suggests that while the drum assembly is set aside waiting for installation, that drive spline hub side of the assembly be supported by a couple of 2x4s or equivalent. This will prevent the spanner nut from being pitched against the clutch drive baskets making the alignment of the nut more difficult.Once the drum is ready to be installed, he inserts his PVC made tool into the assembly to align the spanner nut. The assembly is then flipped over where Mitsubishi’s special tool (part No. MB992332-01-1) is inserted through the four holes in the cover, past the two drive clutch basket

slots and into the spanner nut flange area. Modified striker handles are then used to lift the drum up off the alignment tool and carefully placed into the transmission (Figure 23). As the drum is inserted into the transmission a slight lifting with rotation will be needed to allow the input shaft and pump drive gear to engage.When the assembly is fully seated ,the outer edge will be above the cover tab bolt pads by approximately ¾ of an inch. The spanner nut can now be carefully threaded into the support tower using the special tool. It will take about six or seven turns for it to be fully seated. Once it is in place,

torque the nut to 66 inch pounds plus or minus 8 inch pounds.

To finish the clutch replacement the sealed cover needs to be installed. The inner and outer seals need to be lubricated before installation. To prevent damage to the inner seal during the instillation process, special tool M992314-01 can be purchased. Bob simply uses a 3 oz. Solo Bath cup (Figure 24). Once the cover is in place, it can be carefully tapped down using a dead-blow hammer followed by the installation of the 3 clutch cover tabs and you are done. Once the transmission is installed the Tech In programming will be required for the job to be complete.