TH400 install in a 91 S10 Longbed?

[TRY2HNG]

I have a 91 S10 longbed that im starting a

V-8 swap in. It now has a 4.3 auto. I was going to do a upgraded 700R4 as it would be a easy swapout. But now im leaning toward a street/strip TH400. My truck has the split driveshaft setup. My question is if i order the TH400 should i get a short or long shaft style? also how much x-member work is necessary and will i need to modify the length of the front driveshaft? anyone that has done this setup in a longbed or has knowledge please let me know. The local tranny shop cant answer any questions for me on this topic.

[speeder]

I have had a longbed with a T5 and a 4X4 with ext cab. I am installing a TH400 myself but I am building it first. I know that my 4x4 auto crossmember is not in the right place for the TH400, but summit sells one that is just for the TH400 in the S10. The TH400 is 27 15/16\" from bell housing to mount, but it is only 25\" to the end of the case. This means that with the 4\" 9\" 13\" availabel tail shafts it will be 29\", 34\", 38\" long. The TH700R4 is 23\" to the mount form the bell meaning the TH400 will mount 4 15/16\" backwards of the 700. Also the 700 is 30\" overall length may make your driveshaft just too short or too long. If you have a choice go for a pre 1969 tranny for the direct clutch drum and matching sprag since these are indestructible. If you have a choice also get one with a bolt-on yoke. This way if you break the driveshaft (and since it will be cut and pasted likely) at 80mph, then the yoke will not just slip out allowing trannyfluid go everywhere and ruin your new tranny. If you need help with transmission identification, just let me know. I will need the numbers and letters, like 78 CM, off the metal tag on the passenger side just below the two nipples on the side of the case. Let me know if you need more help.

[TRY2HNG]

thanks for all the info. I was planning on just ordering a Hughes Performance TH400 from summit racing. Im not sure which year they resemble. I was not aware they made a X-member to adapt the tranny to my S10.. Do you know the part number? If not i can just give them a shout. I figured i would have to modify the front shaft. I planned on installing new universals, carrier bearing, and having the shafts checked for balance anyway. The information you posted is very helpful...thanks again!

[speeder]

If you buy that TH400, I am telling you, you need to make sure that they have this problem addressed. If not the TH400 will come apart under great amount of power and torque!

[Wendell]

i have a turbo 400 in my 90 s-10. as far as the crossmember goes all i did was cut the trans mount ear from the crossmember and located it to the rear of the member. worked perfect.

[speeder]

Sweet! Tell us what driveshaft you used, or if you used your original, then tell us what the truck is, please. Thanks ahead!

[Wendell]

i haven\'t got the drive shaft made for it yet. my truck is a 90 s-10 reg cab. came with a 4.3L/auto trans. now has a small block 400 with a turbo 400 trans and i am in the middle of sanding and priming for the paint job.

[speeder]

Thanks a bunch. I am building the TH400 right now. I am still buying parts. guess we need to figure out what the driveshaft sould be. I have some numbers on the tranny but no ideas on the driveshaft. I will go junkyard diving on Saturday, so I might be able to tell you more then.

[z-man]

I\'m not trying to be a smartass, but why use the th400? The s truck is light, and if you\'re building the transmission to handle the power, wouldn\'t the th350 save you some weight and perform just as well? Just curious of any advantages of using the th400. I myself haven\'t bought a trannny yet, still deciding.

[speeder]

this is why <a href="http://s10v8.com/members/speeder/v8s10spec.jpg" target="_blank" target="_new">http://s10v8.com/members/speeder/v8s10spec.jpg</a>

I went out and bought a TCI TH350, thinking it will hold up. No way, after 20ish trips to the track it is stuck in 1st. The TH350 mildly built is limited to ~450lb-ft. The TH400 is the heavy duty tranny of GM and was the one that came in RVs and ton pickups and such. There are some weaknesses in both the TH350 and the TH400, like the intermediate roller clutch.

In the TH400 the pre-70 model trannies do not have the intermediate roller clutch setup, but they have a more efficient sprag setup. This can be replaced by a 34 element sprag, which makes the TH400 bulletproof. The TH350 has similar solution for the roller clutch, but it has another weakness, the sun gear shell, which is made of non-heat treated stamped steel. There is no such part in the TH400 so it cannot break. So although it is heavier and less efficient, it will hold up against a lot more torque. I am so frustrated with spending over $1200 on a tranny and the one I am building with 3 months of tranny research only is going to cost ~ half the TH350 and it will hold up forever. I hope.

[TRY2HNG]

I know that no tranny is failsafe over time, but I have had good luck with TH400s in the past. Few years back I owned a Prostreet Montecarlo SS, It had a Roller 468ci with 680HP and 760lb torque, narrowed Dana 60 ect. The builder of the car chose a TH400. Im not sure what was done to it, but I remember it had a full manual reverse valvebody. 3500 stall. ect. Something else it had installed was a COASTER, it eliminates the tranny from being engauged off the throttle. So when you let off the gas the rpms drop to idle as if you have shifted into neutral. It prevents the thrust load from changing direction on all the moving tranny parts and im told extends the life of the trans. Im sure others in here know more about it than i do. But i made over 60 passes at the track alone and never a problem. Low 10sec runs on monster M+H tires are enough to kill any weakpoints. Just my 3cents.