yup, i learned that the hard way. When i built my 440/727 dart. I went to the salvage yard and bought the 727 and installed it with the 440. I drove it for a while with no kickdown linkage hooked up and by the time i learned that not having it hooked up will ruin it, it had started slipping and acting crazy. I quickly bought the lokar kickdown cable but by then it really started slipping. Needless to say when i got a new trans it was hooked up! Not sure why it hurts them without it or how it works but it does ruin it without it.