Recently I saw a thread on the '70 GS Stage 1 "BB" TH400 valve body. The thread mentioned that Buick engineer Dennis Manner had GMs Hydra-Matic division modify the valve body on the '70 Stage 1s with a valve that allows a TH400 to be shifted manually at any RPM the driver chooses (I believe the example in the previous thread was 5500 RPM, however I could be wrong) without the valve body and governor automatically overriding the manual shift process at a lower RPM than selected by the driver. My question is, is this valve available from an aftermarket source, and is this valve necessary for my '71 Buick TH400 valve body if for example, I wanted to manually shift my car at 5500 RPM. I believe the thread also stated that at some year and point, GM fixed this problem in all TH400s. Right now the transmission is out of the car so I do not know if I can shift it at any RPM I chose without the transmission overriding when I want to shift gears. Since I plan on having the unit rebuilt, I would like to know if I need this valve and where I can get it if necessary. I would like to also know if anyone knows a source for TH400 governors that are preset to automatically shift at a determined mechanically programmed RPM. Thank you for your assistance. Ken
Ken, There was an interview with Dennis Manner in an issue of Musclecar Enthusiast. In it he described the unique valvebody in the 1970 "BB" valvebody of the THM400 that came standard behind the 1970 Stage1 GS Engine. The governor in this transmission was set to shift at 5200 RPM instead of 46-4800 RPM which was the norm. The valvebody also had a special 1-2 valve that allowed the transmission to downshift from 3-1 at speeds up to 35 MPH. Most THM 400's will not do that unless you are in 2nd gear at low speed. They will downshift 2-1, but not 3-1. At 30 MPH, at light throttle the trans will already be in high gear. Flat punching it at that speed will get you 2nd gear, with the Stage1, you would get a 3-1 downshift. This gave the Stage1 motor a lethal leave from a roll. There is a shift kit (Can't remember which) that has that 1-2 valve, and modifying the governor, for higher shift RPM, is easy with the B&M shift modification kit. It just entails alot of trial and error. The Stage1 valvebody did not allow manual shifting. You do not want to manually shift a street 400, you'll wear it out that way. Set it up right with the right shift kit, and modify the governor, and the trans will do everything it should. This thread has some interesting information. Try reading this: http://www.v8buick.com/showthread.php?t=68002&highlight=understanding+switch The B&M shift point modifation kit is here:http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=15697&prmenbr=361
