Originally posted by SlammaDingdong@Sep 1 2005, 01:15 AM
Just another update on this before old Red goes on the jack stands this weekend for a final tranny tweaking.

After letting the latest PCM adjustments soak in for about 10 days i still get a consistently stout 1-2 shift at part throttle. Allen removed 100% TM and did some other magic, which i just love , but the 1-2 still needs softening. Oh well, back to the mechanical side.

General musings about this AVTA deal -

There several different AVTA valve sizes GM uses or has used in the 4L60E. The OE AVTA for a truck will probably be one of the largest valve diameter ones. The tranny pressure curve controlled by the AVTA is very sensitive to throttle input. So I guess large AVTA valve + Transgo + Vette/Billet servos can cause the banging or harsh lower RPM 1-2 shifting. There's just too much pressure on the 2-4 band.

This may explain why a TG install in an F-Body w/ 3.42 gears works fine, but the same setup will splatter your eyeballs in a 4200+ lb. truck with 3.73s. The AVTA used in a lighter F-Body would probably have a smaller diameter valve, thus okay 2-4 band pressure and good 1-2 shifting. It does make sense

Regarding some specific parts this is my general configuration/impressions at this point -

Sonnax Servo Check Valve:
- Get it, use it, you won't be sorry.
- If using vette/billet servos, make sure to drill the check valve orifice using a #31 bit (.1200").

Separator plate:
- The TG separator plate is a low cost excellent upgrade.
- Drill the 1-2 feed hole no larger than .0700" (#50 bit) unless the application dictates otherwise.
- If using the Sonnax Servo Check Valve, for a nice, firm 2-3 shift, drill the 2-3 feed hole using a #30 bit (.1285"). Do this at your own risk if NOT USING the Servo Check Valve!!!

AVTA:
- For a 4L60E equipped truck, assume the larger OE AVTA and use the Sonnax model M-K AVTA.
- Start w/ the the 5 lb. (medium) spring from the Sonnax kit, instead of the white TG spring, for vette/billet servos.

Will let yall know how it goes
The above post was modified by me, at the request of Frank Biolsi from Sonnax. He was very concerned that I had misquoted him and embellished his advice. After reading the post again it was obvious he was right. I have completely removed all references to Frank. The statements and opinions in the revised post are strictly mine. I publicly apologize to Frank and this Forum for this matter.