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The Dual Clutch DCT W6DGA Transmission

Monday, March 30, 2015 - 07:00
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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.

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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 1st, 3rd, 5th and reverse gears. The C2 clutch assembly, when fully applied, drives the even gear hub for 2nd, 4th and 6th.  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).

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