Originally Posted by James B.

There are a lot of close-tollerance mechanical junctions in the driveline. In the torque converter there are splines between the turbine and input shaft and between the stator and stator shaft. In the transmission every steel clutch plate is splined to its drum and every friction plate is splined to its hub. In "drive" the forward clutch pack is engaged all the time and the 3-4 clutch pack is engaged in third gear and overdrive. There are two planetary sets, each with four (4L60E) or five (4L65E) planet gears, each with a sun gear splined to a shaft. From the transmission you have the Slipyoke splined to the output shaft. The yoke has u-joint, each with needle bearings. If the truck has a transfer case add all those mechanical junctions. If the truck has a two piece driveshaft there is a slipyoke and splines there with another U-joint. At the rear end it goes through another u-joint to the pinion shaft. The pinion yoke is splined to the pinion shaft. Then there is the pinion to ring gear lash. inside the differential there is tollerance between the spider gears and their shaft, and lash between the spider gears and axle gears which are splined to the axle.

The point is, there are dozens of places where torque moves from one part to the next connected only by the tollerances between the parts. Setting up the shifts too firm is like turning the driveshaft with an impact gun. Inside the trans you have aluminum clutch hubs and drums splined to steel clutch packs. These aluminum parts do not handle instantaneous torque spikes such as those experienced during jolting shifts. Secondarily, jolting shifts also affect your belt tensioner's life, motor and trans mounts, suspension bushings, and belt life. With violent upshifts the motor drops RPM so rapidly that the accessories overrun the crank with great force. If you could watch the serpentine belt during a jolting upshift you would see the tensioner bottom out to its maxed position and the belt ride up in the groove of each pulley. the accessories will slip on the belt as they overspin it.

The more thrashing the driveline takes the more quickly all these tollerances between parts will losen up and get sloppy. The rear differential and axle splines are the first to suffer since the pinion and ring gear are multiplying the torque from the driveshaft by a factor of the gear ratio.

I don't like alot of play in the driveline. The best way to keep it that way without sacraficing the way you want to drive is setting up the WOT shifts to be civilized and not jolting.

The band in the 60 is wrapped around the reverse input drum. It is engaged by a pin with two pistons, one for second gear and one for fourth (OD) gear. Installing the "Corvette Servo" affects only second gear since fourth is handled by a different piston. Bands are semi-self-energizing. Trying to engage them too quickly will result in violent grabbing and a jolting shift. Some people are amused by the tire barking this causes during the shift, only because they don't understand what an absolute hell this is on the parts. This limitation is one of the factors that holds down any trans that uses bands to shift from smoothly scaling up to higher power-handling. (Incidently, TH400 and 4L80-E transmissions do not shift with bands, they use all clutch packs. Bands in those units are used only for manual overrun or reverse.)

I will always cast my vote for a smooth but firmly shifting trans calibration over a solid jolting setup. Everything will simply last longer and provide a better ride.