The 6L80/90 converters have had numerous problems since they came out in the mid 2000’s. There have been problems with the converter, along with problems in the transmission causing problems in the converter. Most of these problems have been related to the converter clutch lining wearing away until the clutch is metal to metal on the cover of the converter (Figure 1), causing metal contamination through out the transmission and cooler system.
Several of these problems have already been discussed in previous issues of GEARS. There is the broken or leaking rivets that hold the damper assembly to the piston, and the worn valves in the valve body and pump causing the converter clutch to slip.
One other problem with this converter is the design of the front cover that the lock-up piston clamps to during lock-up. The OE cover on this converter has three large mounting pads welded to the cover to prevent cover cracking and flexing under load.
When a converter is welded together, it has a tendency to shrink during the cool down process. Since the cover has the large mounting pads welded to it, it resists shrinking in the pad areas, but shrinks between the pads. This causes the clutch surface to no longer be flat, resulting in a leak between the piston and cover during lock-up. This is evident on the few covers that have not been destroyed by the metal to metal contact.
Figure 2 shows an OE cover mounted on a flat surface of a converter balancer and the pads marked 1, 2, 3. When using a dial indicator and rotating the cover each pad area goes back to .000 on the indicator, but varies from .009 to .014 between the pads. This problem will even be worse if the cover is machined flat by removing an already thin cover.
The best way to resolve this problem is to replace the OE covers with a steel billet cover from the aftermarket parts distributors. The billet covers are almost 1/4 inch thicker in the clutch surface area than the OE cover as shown in figure 3. The billet cover will resist flexing after welding and bring the converter back to OE specs for proper converter height.
As transmission builders, always request billet covers on your 6L80/90 converters.
Article courtesy of GEARS Magazine