A "Shift Kit" won't give the trans any more torque capacity. It will allow it to shift quicker, which reduces heat build-up in th trans and fluid. If the trans is in good condition now, and not slipping, or doesn't have a "delay" when you first put it in gear, you can put a "Shift Kit" in it, and shouldn't have any problems. Just remember, a shift kit is not a cure-all for an ailing transmission.
It might be a good idea to do this if yer puttin in an engine that will actually be able to take advantage of it. Too many times I see people insist they have to have a shift kit in their cars, but they just don't have enough engine to make it work right.

Here's the one I use the most, and highly recommend for most street driven cars. This kit will shift a little more firmly under "normal" driving conditions, but not bang yer head. When you stand on it, tho...it will rock & roll. Just be sure your u-joints and mounts are all in good condition.
I would also recommend putting a new modulator on it at the same time. Just good to do.

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HEY!! Tux is answerin my mail!!! Adams' Apple2007-02-23 20:16:57

Joel, I would like to absorb some of your "brain ooze". Was wondering, what would be the ball park cost of having my TH350 rebuilt. We have a shop close by that will do it but he's into heavy duty components and stall clutches. Not my cup of tea. I can rebuild manuals in my sleep, but have never attempted a "slush-o-matic" or I'd do it my self. Any help would be appreciated.

Joel,

Jim: P/M sent.

Tim:
The 400 can benefit from a "shift kit" just as much as any other trans. Superior has kits for just about every one of them.
If your 400 is shifting early, try adjusting the modulator screw in a few rounds. It's at the pass. side, front area of the trans, pointing toward the outside of the car. Take the hose off, and inside you will see a small screw. Twist it in a couple of turns, and it will shift later. If not, the mod. is bad. If there is any fluid that comes out of the end of he mod. when you take the hose off, the mod. is ruptured.
This could be the reason it doesn't take "passing gear" like it should. There is also an electrical solenoid inside the trans that controls the kick-down, or passing gear. If it is not working, passing gear will not always work, either. It(kick-down) requires the input of the modulator, and the solenoid to operate properly. If either one is not working, passing gear will suffer.

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Thanks,  I will try that.  I recently had the hose off of the modulator to re-route and did not notice any fluid.  Someone had the the hose pinched between the mod. and the cooler lines.  Can the shift kit be installed all from underneath??

[QUOTE=71Shark]...Can the shift kit be installed all from underneath??[/QUOTE]

Yeppers...iffin ya don't mind all that fluid runnin down yer armholes!

Where can I get one ?