I have a 64 riv w/ a 425 nailhead. i'm new to buicks so i will try not to humiliate myself. I was wondering if there were any differences between an st400 and th400. the reason is that I want to re-build the trans. (only 33k on it but it sat for 30 years in Denver, co. in a garage and it leaks a little) I plan to re-seal atleast, maybee replace the bands too. any suggestions for a rebuild or possibly shift improver kit? Also I have heard that these trannys sometimes take off in second to prevent tirespin, can you bypass this?
Buick called their THM400 the ST400 (Super Turbine 400) The 64 ST400 had some differences in the valvebody that make it unlike the 400's that followed, but the 65 and up ST400's were THM400's It is unwise to install a shift kit in an old transmission. It is better to do it at rebuild time.
A transmission sitting for 30 years isn't good. Fluid oxidizes, friction elements deteriorate, and worst of all the rubber lip seals internally will harden. It may work, but it will be in for a short life in any case. I would agree with Larry and recommend rebuilding it. I have a post here to help the DIY'er rebuild their TH400. Lots of information and pics that will hopefully help some tackle it. http://www.nastyz28.com/forum/showthread.php?t=58578 You can use my instructions for dual feed and valve body mods to make a nice crisp clean firm shift without it being brutal. This method is proven to at least 800 HP or you can use the TransGo Reprogramming kit. It works well but runs into issues at about 500 HP in my experience.
