Lockup and Non-lockup Transmissions
Production of lockup transmissions started in the late 1970s as a response to fuel economy concerns. The purpose of the lockup design was to temporarily eliminate the normal slippage that occurs with non-lockup transmissions in order to increase gas mileage. Lockup occurs in the torque converter. However, lockup is controlled by the lockup valve, which receives a hydraulic signal from the governor at a predetermined speed. In non-lockup mode, the torque converter has a pump that transmits and multiplies power by pumping oil against an internal turbine which is in turn attached to the transmission input shaft. There is also a fixed stator between the pump and the turbine which redirects the oil returning from the turbine to prevent it from hitting the pump. For a simple idea of a torque converter in non-lockup mode, imagine two fans, with the first one blowing against another one which is off. The blades on the second fan will also turn, but not as fast as those of the first fan because energy is lost. In lockup mode, there is a clutch that engages between the turbine and the pump to physically connect the two components. Going back to the example of the two fans, now imagine that the shafts of both fans are somehow connected. Both the blades of the second fan will turn at the same speed as those of the first.
Below is a picture showing the differences between lockup and non-lockup transmissions. Lockup transmissions will have a smooth end on the input shaft (no splines) for the first 3/4", then splines will begin. The non-lock-ups will have splines to the end. Lockup converters can't be used with non-lockup transmissions, nor can non-lockup converters be used with lockup transmissions. Photos:
Source: How Stuff Works - Article by by Karim Nice
- Lockup and non-lockup input shafts (Courtesy of www.technicalvideos.com.)
- Diagram showing power flow through torque converter in lockup and non-lockup mode (Contributor unknown)