I have not previously built any 4 speed lock-up transmissions but I just rebuilt my 4l60e transmission with a TCI overhaul kit that includes an Alto 9 friction stack-up for the foward clutch pack that replaces the original 6 friction arrangement. The clearance was only .015" after assembly which is less than spec {.030-.063"}, but I had no selective backing plate to correct this.
The 2-3 shift at part throttle is quick, but immediatly after the shift, there seems to be a slight drag {for about 1/4 second} like the band is not releasing quick enough. It shifts fine at WOT in all gears.
I installed a shim {from the Transgo SK series L shift kit} behind the 2nd servo piston housing per instructions, but took that back out last night and the 2-3 hang time thing is still there at part throttle. The original servo return spring was used.
The accumulators are set-up like this: 3-4th accumulator spring went in the case first before the piston.
1-2 accumulator piston went in the housing first and the orange, white and white triple spring arraingement from the Transgo kit.
Foward accumulator spring was replaced with the white spring from the tCI kit.
Only other mods were SPX Filtran beast sun shell with wide bushings installed on the sun gear, Sonnax .490 boost valve and I'm running a TCI 3000 10" stall converter with 12" lock-up piston.
What should I do to get rid of this 2-3 shift hang time?

 

The problem with the 2-3 part throttle shift is the 2-4 band is not coming off fast enough, because of the .015 3-4 clutch clearance. It should be .030 - .040 clearance. You might try adding a stiffer return spring on the Corvette servo, to help this out, & or otherwise open the band release hole.

 

Thanks for the reply. I noticed that original return spring is not real strong. How stiff of a spring can I use without interfering with the apply pressure of the servo piston?
Where exactly is the "band release hole"? Would that be the outermost hole in the case outside the 2nd apply piston and piston housing, and to the inside of the 4th apply piston and servo cover? If so, what size do I drill it to?
Thanks for the help!

 

I replaced the stock servo spring with a TH-400 coasing band spring, which is almost twice the return pressure but still have this problem, but only after cold start, 1st time 2-3 shift. It seems to be way less of a drag with the car anytijme after the first 2 - 3 . I am currently running a stock 700r4 converter, as my TCI unit went back for repairs. And just for diagnostic sake, I installed a stock 2-4 band.
Also, I added a Sonnax check valve 77701-076 , shown here then I pulled it back apart and shimmed that3-4 clutch stack-up to .038 with selective backing plates. Also, I have tried shimming the 2-4 servo housing with the shim provided with the Trans go