Hi, i was about to swap my transmission for a rebuilt one but now the man at the shop holds me off telling me i don't have a th400 but a st300. On the outside everything looks the same as any other th400 i've ever seen so is it possible that some st300's were built looking the same as the 400? The ID tag is gone so i can't tell what it is. My car is a 71 Riviera and has the TCS solenoid at the carb, i thought an st300 is switch pitch and has nothing to do with TCS am i right?
Hi David, The ST300 is totally different to the TH400. check out the pictures of the two bottom pans... http://www.charlietranny.com/ST300Buickbottom.JPG http://www.charlietranny.com/400THMChevybottom.JPG TCS has nothing to do with it. TCS was installed to pass emission laws by only allowing distributor vacuum advance in third gear or reverse. It is combined with the thermo vacuum switch mounted in the water passage on the inlet manifold. Skip all of it and use a ported or unported vacuum source for your distributors vacuum advance. Follow Larry's "power timing" thread found as a sticky in the Buick FAQ.
Hi Christian, what you are telling me is exactly what i told the tranny guy, but he keeps telling me it's a rare st300 that looks exactly the same as the th400 on the outside but differs inside. It's weird anyway that he knows that without even seeing the inside of my trans...
If it is an ST300, on the driver side of the trans there should be a two prong electical plug. One prong should be vertical and the other horizontal. One controls the front pump that activates the VP Torque Converter and then the other prong is the kick down. That's the easiet way I know of to tell a TH from an ST transmission. And if it looks just like a TH400, and it's a ST, then it is probably an ST400. The ST300 is a two speed and the ST400 is a 3 speed.
The connector looks the same on my '70 trans, and probably also Davids '71 trans, but one prong is used for the TCS and the other for the kick down. Maybe that is why the shop guy think it is a ST o No:.
Maybe he means to say that you have a TH375 (they look like the TH400)? More here: http://www.v8buick.com/showthread.php?258481 Devon
the 375 is like a 400 but with a 350 output shaft, i have the long tailpiece with the long shaft and it looks different from a 350 long tail.
You can tell a 400 from a 300, a 375, or about anything else by the diameter of the output shaft. Also the yoke sliding onto that shaft is larger. Most yokes are 1.89", though some early ones were 1.69". From 68 on all used a BOP pattern (except Chev). The 300 had a 12" torque converter; the 400 a 13", but they will interchange. The switch versions were only built through 67; the primary differences were the front pump & torque converter. Bruce Roe
I'm new to the forum, but this is a great question to follow. I also have a 71 Riv that needs a tranny rebuild, I have the 455 engine and th400 trans from a 73 Electra 225, will it be the same? I assumed they were both long shaft trannys, and the bolts would be the same. It would be a little easier for me to get the one rebuilt that is already out, then do a switch out. I'm keeping them both anyway. Any input is appreciated. Jim
Problem solved, the tranny guy finally admits i'm right, so it's a th400. I also found someone else who sells a rebuilt, reinforced and modified trans that came out of a 75 Estate, this is a BC-code tranny while the Riviera has a BT, anyone knows what it is inside the trans that makes the difference between a BC & BT? Not that it matters much since it's modified anyway but i'm just curious.
Never mind my last question, here's the answer: http://www.v8buick.com/showthread.p...-between-th400-types-BB-lt-BC-gt-BS-gt-BT-ETC Thanks all anyway for the replies !
The 375 has a th400 yoke diameter,uses a 400 yoke that has a smaller outside diameter,but the inner splines are the same as the 400.Been there,done that.I still have a tailshaft from a 375.BrunoD.
Here are tail housings from a 400, and a 375 above, number cast in. Difference in dia is pretty obvious. The yoke dia for the 400 is 1.89"; some early ones were 1.69" Since the 400 splines are about 1.36" dia, that gives a min yoke thickness of .265" or .165". The 375 yoke dia is 1.50". Putting a 400 output shaft thru that hole would leave a yoke thickness of only 0.07". The 375s I've seen had only 4 clutch discs (instead of 5 or 6 in a 400), and were used behind small blocks. Saw them for 68-72; after that apparently used TH350. Bruce Roe
