I'm looking for either a BB code trans with a broken case, or at the very minimum, a valve body from a Stage 1 BB trans with the valving that allows the 3 to 1 downshift feature. So I can either buy what you have, or borrow to replicate the special parts in the machine shop I work at. Thank you, Tom Miller
Hi Tom,would you be able to use any 400 trans,or it will have to be a BB trans ?If you can use any 400,I can let you have a used one for $100.00plus the trip.Bruno.
Hi Bruno, thanks for the reply. Thank you for the offer, but No, a regular TH400 isn't going to provide me with what I need. I don't NEED a transmission, I really only NEED the valve body out of an original Stage 1 BB code trans, that has special valving in it that allows a downshift from 3rd gear all the way down into Low gear at speeds all the way as high as 30-35 mph. I want to make a non BB code trans perform this downshift feature, and if it looks like something I can replicate, I can write a program and make several of them at work in a cnc turning center.
There is a really good article in a thread explaining that: 1. Hydramatic changed transmission settings more frequently (model year) than engines; 2. The '70 'BB' TH400 had the special 3-1 direct downshift feature; and 3. The '70 'BA' TH400 had the same valve body as the '70 'BB' except for a check ball in one circuit. Meaning .... remove that check ball on a '70 'BA' valve body, and you have your 3-1 downshift.
I don't think it's that simple. I was/am under the impression that there is a specially machined shift valve that makes the magic happen. Thanks for the replys gang
I am pulling this text below from another thread on this Board about the same subject (or close to it). Regarding Stage 1 identification (and the specific 'BB' code TH400): Automatic transmissions have a tag on the passenger side (figure T2) that contains the code identifying the transmission application. Stage1 GSs came with heavy duty transmissions with a 2.48 first gear. ALL had (or were supposed to have) steel flat washers (instead of wave type) and 6 plate clutch packs (instead of 5 plates with wave washers). These types of transmissions were referred to as a 'Cadillac sprag' transmissions, and were used in high torque applications. The servo spring was different, in addition to the valve body pressure. The following was taken from a post on www.v8buick.com by TH400 expert Mark DeConti: "The 70 BB Stage 1 was unique. The later valve bodies were not setup like it, though close. Not all 70 Stage 1 BB's had the 6 clutch drum, it depended on the build date as it was used after a certain point. A lot of 70 BA's had the 6 clutch drum too. The BB's used a different direct piston which improved the 3 gear shift. The 70 BA valve body is VERY close in design to the 70 BB and only a spring in the 1-2 accumulator valve needs to be removed to make it the same. No waved steel plates were used in the 2nd and 3rd gear clutch packs on the Stage 1 trans, and the 3rd gear valve body accumulator spring was softer to firm up the shift. The governor was setup to shift at approx. 5500 rpm and was specific to 1970 BB only (some model of Pontiac and maybe Olds used it too). Later governors were ok, but closer to 5200 rpm. The valve body separator plate has larger holes in places to increase pressure to the clutches. Am pretty sure that 70 was by itself and 71-72 was different." ............................................................... "On the 70 models, higher rpm governor. no wave plates in 2nd and 3rd clutch packs and the 3rd clutch piston was different on 6 clutch pack units. Valve bodies were setup for firmer shifts (1-2 accumulator valve spring removed and softer 2-3 accumulator) and shift plates were different. Some of these mods were carried over to 71 and later, but not as extensive as 70. Also, not all 70 Stage 1 trans had 6 clutch 3rd packs. The 5 clutch packs were used until a certain build date in both. Then both used 6 clutch packs with the Stage 1 units getting the special piston. At least this is what I have found on the ones I have worked on." ............................................................................. There are also several articles referencing prior interviews of Dennis Manner, former Buick powertrain Engineer (and regarded as the "father of the Buick 455") who claimed that he had to persuade Hydramatic and other Buick brass to build the 'BB' TH400. I think Denny's words were quoted as having to "fight" Hydramatic and other Buick brass to build it. Denny wanted the 3rd gear direct downshift to 1st gear for GS Stage 1's out on the street "doing battle" using rolling starts, etc. No 3rd to 2nd downshift below 40mph-ish, just direct to 1st gear and RPMs. Inquire with others who've experienced it ... it is pretty stunning.
