Tech Tip: Correctly installing the 618 Cummins converter front cover bushing
Great care must be taken when installing the front cover bushing in the 618 Cummins converter because of some critical flow issues. The converter charge oil flows through the input shaft and exits in the cavity between the turbine hub and cover. The oil must then pass through the passageways created by the six notches on the outside diameter of the bushing. (Fig. 1)
Because this oil is also torque converter clutch (TCC) release oil, a sufficient amount of oil must pass between the TCC Piston and the cover, to keep the clutch from dragging when the converter is not in lockup. When the TCC release oil is restricted, the clutch will drag on the cover and burn up, in the same manner that it does when the clutch is slipping on apply. Both conditions will destroy the clutch and result in 740 or 1740 codes. Most rebuilders are aware of the flow restriction caused by installing the bushing too deep in the bore. However, many rebuilders may not be aware of similar restriction issues caused by not installing the bushing deep enough. The bushing in Fig. 1 was installed flush with the thrust washer surface of the cover. When the bushing is in this position, the thrust washer blocks four of the six passageways on the outside of the bushing. The restriction of release oil caused the clutch in this converter to burn up prematurely because it was dragging on the cover.
When the bushing is installed properly it will be recessed, just below the oil reliefs that are machined into the top of the busing bore. (Fig. 2) The step on the bushing installer (Fig. 3) is designed to install the bushing to the correct depth every time.