Originally Posted by baz57
I'm showing my ignorance, but how do you mean lock up? On rapid acceleration the box is great. Fast smooth change. But when pottering around town, all changes are slightly ponderous, slow and a tiny bit jerky. I drove a jag with an 8 speed box which was super smooth too.
Traditional auto boxes use a torque converter instead of a clutch. This gives the smooth change, but also will cause revs to rise disproportionate to the speed when you accelerate a bit like a slipping clutch feels, but intentional. When the box is locked, the torque converter doesn't cause that 'slush box' slipping clutch feeling when you accelerate in gear.