Shift kits.. do you really need one????

I got this from another forum.. this nis sort of what I'm talking about..

"The valve body, itself, has only limited control over the overlap period. When the valve body commands the 2-3 upshift, fluid is routed to the kickdown servo to release the band and fluid is simultaneously routed to apply the front clutch.

If the kickdown band is properly adjusted, a known quantity of fluid is needed to release the band but, because the clearance in the clutch can vary widely (and isn't adjustable externally), the quantity of fluid required to engage the clutch can also vary widely.

If the front clutch clearance is at its tightest allowable factory tolerance (.025"), a mere 7 CC's of fluid is required to engage the clutch while 27 CC's are needed to fully release the band. As one can see, with this much discrepancy in fluid quantity, the clutch will tend to apply before the band can release; big time overlap.

If the clutch clearance is at its maximum allowable factory
tolerance (.125"), 34 CC's of fluid are required to engage the clutch. This discrepancy in fluid quantity would tend to make the band release too soon before the clutch can engage and you have engine RPM flareup. (Since the trans is technically back in 1st gear)

Additional factors that can influence the overlap are the size of restrictor orifices in the fluid circuits that limit the velocity of fluid flow and the configuration of the return springs in the servo/clutch.

If one is assembling the transmission, the proper choice of clearances and spring combinations goes a long way to attaining the proper overlap, but if one is working with an assembled unit , already in service, adjustments are limited.

Attaining the perfect overlap period with all of the possible variables is akin to choreography; this is what the reprogramming kits attempt to do, to balance the action of the valve body and the existing hydro/mechanical components it controls."