My '67 Skylark carries a ST-300 trans and I am squeezing in a '73 455ci and need a heavy trans to handle it. Keeping in mind I'll be using E-bay and my local salvage yard as resources, what "type" of TH400 should I be looking for? I know there is different shaft lengths and something called a ST-400 and the usual TH-400. But What's going to work best for me. Short shaft or long shaft, ST or TH? I want to stay away from chopping my driveline and would have whatever trans I find inspected and rebuilt. Thanks for the source to post V8BUICK.COM! Gabe
Gabe, I believe you'll want a short shaft TH-400. From 65-67, Buick called it the ST-400 because it was a switch pitch transmission. It was still a THM-400 though. I have a 1967 ST-400, code BT. I originally had a 13" converter that had stall speeds that were really too low.(2300/1100). Just replaced the converter with a 12" from Tri-Shield-Performance. What a difference, now I have 3200/1800 Stall speeds. The ST-400's were great transmissions. The only problem I had besides the wrong converter was the valvebody. These cars originally had a throttle switch that turned on the high stall at idle and wide throttle openings. Buick engineered the valvebody to have an earlier 2-3 shift because they intended the car to accelerate on the converter. I discovered this when I played with the governor to get the shift points higher. I could get the 1-2 to 5500, but the 2-3 would go much earlier(4500). The valvebody also has no 3-2 valve, so it had no part throttle downshift, just full throttle. Remedied this by putting a later model valvebody into my trans(1971 BC) The earlier trans used a more restrictive filter assembly(cannister) rather than the flat (broiler pan) type filter. When I switched over to the newer valvebody I was able to use the flat filter. If you want to use a switchpitch, look for a 65-67 ST-400 short shaft trans or get a later model trans and convert it over. There is a tag on all THM and ST 400's that tells you what car and engine it sat behind. If you can find a 400 from a high performance car, it has a better valvebody and in some cases added beefing from the factory. Ron Session's book "How To Work With and Modify The Turbo Hydramatic 400 Transmission" is a great book, and will give the codes for 400's of various makes. As far as Buicks are concerned, the 1970-72 BB and BA trans are the hot ones. They are hard to find. Good luck.
