Originally Posted by nevrenufhp
It fuels harder to the point of shifting, and you can carry each gear a couple more mph. If it shifts at 2400, and the engine can rev to 3100, it needs a kickdown cable adjustment. It makes a difference is all I'm trying to say. Test it out, and you'll see it get up to 40mph faster than before.
We did with the 12 valve 4 and 6B's in the bread fleet.
What we found was...unless you adjusted the trans (and the procedure I am not familiar with, it was done by the shop we used for Allison repairs) it made no appreciable difference. When the transmission was
adjusted to shift at a higher point, as you suggest, it made the shifts kind of violent and very unpleasant in everyday driving. It was as if the "kickdown cable" had become too sensitive. The shop was never able to find a happy medium.
Perhaps on a 1/4 mile run, the truck would get to the finish faster if you adjusted the trans to shift further up in RPMs. In daily driving, the guys that did the test were happiest with them shifting at the normal points, which made messing with the springs unnecessary.