Yea - this topic has been beat to death. But, not all questions seem to have been answered (did a lot of searching).

Things you need to swap in a TH400 (from a 700R4)
1) TH400
2) Either the Hurst kit (PN 5500002) or a Spohn TA for the 400.
3) A shorter driveshaft with the front yoke for a TH400.
4) Electric kickdown kit (Hurst PN H2488605)
5) Adjustable Vacuum modulator (Hurst PN H6500001)
6) Speedo mods to get an electric speedo to work

Item 1 is no problem
Item 2 leaves only one question. What if I later add a gear vendor's overdrive unit. I wonder if the Steve's setup will work with that. I need to give him a call.
Item 3 leaves a question. Everyone says to shorten the driveshaft. But, I have actually talked to others who said you have to lengthen the driveshaft. I take it that this may have something to do with the different tailshafts for the 400?
Item 4 is not a problem.
Item 5 - ouch. Anybody running a TH400 on a car that doesn't produce a lot of vacuum? My 230/245 cam doesn't produce much vacuum. Any foreseeable problems with this.
Item 6 - ouch. Has ANYONE installed a TH400 on a car with an electric speedo? I know that www.jagsthatrun.com offers the speedo conversion stuff. But, just curious if anybody has used it or how it is being done.

Did I forget anything?

I am asking this because I am pretty sure that I will be going with a TH400 when the 700 lets go. My 700 has never been rebuilt so it shouldn't last much longer. I was going to learn to rebuild the 700 myself but with the kind of power levels I expect in the future I don't believe the 700 would be able to take it. I'll eventually be running a Vortech YS trim and putting down enough horsepower for low 10's.

Tim

 

Item 3 - there are 3 tailshaft lengths for 400s. Details may vary, offer not good in all 50 states, your warranty gives you specific legal rights.

Item 4 - DON'T get that "adjustable vacuum modulator". It sucks. Just go to the parts store and get a "red stripe" one. There are 3 other common VMs for PG, 350, & 400, all of which are a small gold-colored can: green stripe, pink stripe, and red stripe. The "adjustable" one is a big black can. Stay away from that. Look the VM up for something like a 72 Monte Carlo 454, and look in the box to make sure it's the red stripe version. It is somewhat adjustable also. You know how to get me if you need details.

L8r

 

Tim, wouldn't you just get a full manual or auto/manual valve body?

it will shift even with the most aggressive cams. Mine is an auto/manual valve body. and it works fine. shifts a bit high for most in "auto" mode but manually it shifts fine at what ever RPM I like higher in the band:lala:

its the part I totally don't regret doing. everything else may change one day on my car but that sure won't!

 

There aren't many long tail TH400s out there they were mainly in trucks. You want a short tail TH400 and it requires a longer driveshaft. Driveshafts can't be lengthened so you'll have to get one made or get the one ready to go from Spohn. Just run a manual valve body

 

You won't really know what length driveshaft until you get the tranny in and the yoke installed. I have 2 different slip yokes. One is for a standard GM u-joint that was out of a 1968 car and the other is for a 1350 series u-joint that I ordered from the aftermarket.

You determine driveshaft length by sliding the yoke into the tranny until it bottoms out then pull it out 1". You then measure center to center of the u-joints to get the length of the driveshaft. My 2 yokes have different measurements. The 1350 series yoke doesn't go into the tranny as far as the other one so it needed a driveshaft a about an inch shorter from what the other slip yoke would have used. If you think you're going to produce enough HP that you need a TH400 then don't even think about using a stock driveshaft. Get a new one made from 3" x .083" steel with whatever series u-joint ends you intend to use.

Since I have a manual valve body with a transbrake, there's no vacuum modulator. The transbrake solenoid goes where the modulator is.

 

If you go with a manual valve body setup decide if you want engine braking when down shifting or letting off on the throttle. I was told that to have engine braking you can only get a forward pattern valve body. I had a reverse pattern manual valve body in my 700r4 and that didn't have engine braking. It was awful for autocrossing and road racing to not have engine braking. If you are just street racing and drag racing maybe that's not important to you to have engine braking.

 

Guys - What about the speedo? Has anyone with an electric speedo converted a TH400 or TH350 to work?

Tim

 

I'm not sure about getting the speedo in the 400 to work, I have to figure that one out tomorrow when I put my th400 in my car, but on the th350, if you have a short shaft tranny you can find the housing off a olds. th350 and it has the big hole and your 700r4 speedo gears will fit inside then. if anyone knows how to get the 400 to work please let me know. One more thing, I ordered the hurst th400 kit, does it come with what I need to make the kickdown work?

 

Very late 80's or 1990 only, TH400 has an electric speedo. In 1991, GM changed to the 4L80E. Parts should still be the same.

I don't know if the speedo gears are interchangable between models. I don't think so.

 

I was reading on camaroz28 and some had mentioned in their 96 Z28, they had to change the shifters as well? Is this the same for our cars? Or is it part of the hurst part numbers?

 

If the car originally had a 4 speed auto (700r4/4l60e) then yes, you would have to make some shifter modifications because the th400 is only a 3 speed. The Megashifter has a spot to install a stop pin when you convert it from a 4 to a 3 speed controller.

 

so whats the good word on third gen F body th400 tailshaft housing brackets? are they made yet, and if so then by who ?

thanks!@