Years ago I dropped off a perfect shifting 32K mile 70 T400 to be built for racing. Was a little late in picking it up and the trans shop said someone else needed one in a hurry so they gave him mine. I was really pissed.... They tried to tell me the 76 Caddy trans they build for me was better and it had a stronger case. I reluctantly took it and put it in race car...never shifted right 1-2. Took it back to them and they went thru it again. Same deal...GRRR Let another shop have at it and same again. GRRRx2 I'm thinking some sort of internal leak or porous casting? 2 questions: 1) is 76 Caddy case really stronger? I heard some T400 cases have support ribbing that makes them better. 2) anything internally better or worse with the Caddy trans Thinking of taking it to ATI to have them build it since they have a dyno that they can test it on. Mark Deconti? Are you there?
I do not know what is wrong with your trans, but the 76 Cad trans was built for a 500 hauling a heavy car. You get a 6 friction direct clutch (instead of 5) in those, but who knows what the shop did. I use a 70 Cad (472) converted to switch pitch in my Olds. I would first do a pressure check at the port. OK, I might swap the valve body/plate. I once sent a switch pitch pump setup to someone, and after a long time his shop said it was bad. I said, send it back to me. What they sent was a completely different setup, proof was in a different number in the casting. Who knows where my parts went to save someone else? 4 decades ago I gave decided I must do my own transmissions. good luck, Bruce Roe
Yeah last guy put a whole different valve body in and shimmed the pump spring. said it would "knock my socks off" on the 1-2...nope. No fun putting a trans in that not knowing if it will work right. that's why I'm thinking dyno test and real time pressure readings. More money but worth it. If not right they could re-case it. Some of these trans guys are overly confidant. Last guy said he could do a T400 in his sleep. Maybe that's what happened......
The link above explains the case differences for BOP TH400. The stronger case was mainly used on long tail units, but some short tails did have them. What is the issue you are having? Soft shifts or not at the correct point? The 2nd gear shift uses the center support, direct drum with sprag or roller, accumulator and the intermediate clutch plates. There are some instances of case porosity or cracks where the center support is bolted to the case. Another issue which can occur is the drilled passage to the accumulator. There is a pressed in plug (bottom left of first pic) to seal the drilled passages that can either leak or even fall out. I will try to post pictures of the plugged passage and the center support bolt (three holes in center of pic 2) location. Look at your case to see if anything does not look right. There are also 2 types of center support pistons. "most" pre 1973 pistons were cast aluminum (pic should show that) and starting in 73 the piston is metal with a plastic spring retainer. Both should work, but anything is possible. By 1976 "most" direct drums were 8 element rollers, even if they had 6 clutch plates. These plates are for 3rd gear and do not effect the 2nd gear shift. The roller assemblies are weak and do not hold as well as the 34 element sprag. Hopefully the early drum was used with the sprag in you transmission. The accumulator is used to soften the 2nd gear shift and is located under the low servo piston. Some builders will disable it to firm up the shift. If not, there are 3 different springs that are used to make the shift softer or firmer. Blue, black and yellow. The valve body has an accumulator valve which also controls firmness. There are two styles of valves, but both can be modified. Generally, the stronger the first spring installed in it will make firmer shifts. Lastly, giving away your transmission to someone else should NOT have been done! Hope this gives you something to go on.
NOTICE: The heavy case th400 is a real unique item and almost unknown. Read the CK Performance item shown in an above post and take notes. These cases have a part number that ends with 500 so I call them "500" cases. Part number is just front of the dipstick . 500 cubic cadillacs used them, and many other heavy body cars and station wagons used them. The pan rail is almost double thick, and bell housing is obviously reinforced, etc. Buy them up before they are all gone. The Chevy boys are secretly buying all our BOP (bcop) "500" cases and adding their own racing ULTRA BELL 400 adaptors. Chevy made NO "500" STYLE CASES. Hurry BOP guys, while they last. You can use an 8 bolt pump where you have 8 Threaded holes. If the 2 extra pads are present but no holes, just drill and tap the pads. A 6 bolt pump fits all without leaking.
These cases are not as rare as ppl think but I have found more in long shafts than short shafts This one show some of the extra reinforced area of the bellhousing, and you can see the thickness in the bolt are are. The pan rail is harder to see in the pics.....has a thick extension housing area area....and a huge internal web https://m.facebook.com/marketplace/item/648404657063131/ https://m.facebook.com/marketplace/item/1280426252523563/ https://m.facebook.com/marketplace/item/5676772299032621/ https://m.facebook.com/marketplace/item/1327687824631416/ There are at least 3 I see in add https://m.facebook.com/marketplace/item/452266477036284/ And a few adds that looked like it but I couldn't 100% says yes too. Best way to tell is the internal webbing inside the bellhousing
The bell housing exterior has 2 steps around the bolt pattern. Can be noticed even if bolted to an engine.
The photo of 4 tranneys, you see "2 steps" on the one shoved foreward behind the truck cab. It's a "500" for sure.
Buy all the 1970 thin case junkers you can find for parts: short tail trannys for all internals and tails. Put those parts in the 500 cases. 1970 has smooth drum sprag, good valve body, aluminum pistons, reinforced center support ring, 8 bolt pump etc,wow
Most th400's even with 500 cases, made after 1970, have downgraded cheaper internals. But with good parts installed, and a 500 case you are ready for well over 750 hp and all the torque you can put to it.
Mark, here is the infamous RAFFLE trans that you built that I won in BG in 1996 in BQUICK. At least a thousand passes on it and shifts great....like day one. Looks like HD case.
So my 70 case may have been HD? So he really did get over on me....Here is a pic of a 69 HD Buick case.
