hi i was wondering if there is a difference between the 2wd and 4x4 versions of the thm400. I am looking at buying one out of an 79 gmc 3/4 ton 4x4 truck. Wanting to put it in my gasser. It will see the strip on most weekends and street during the week. I also plan on installing a shift kit (reprogramming kit) i still want the ability to manual shift but also to pop it in drive and let the trans do the work. Here is a direct quote from another thread "a 400 turbo when manually shifted into low gear and left in low gear with the shifter...when the motor reachs top RPM the 400 will shift into 2nd gear on it's own (like an air shifter in a drag car)" can someone explain this more in depth
different output shaft. When you assemble the transmission, the output shaft is almost the first part you install. That means you need to take it all apart to change it.
It'll work if you take the trans apart and replace the output shaft with a 2wd shaft, and also buy a tailhousing.
sorry i am new to all this couldn't i just get a yoke to fit the output shaft? I believe my driveshaft will need to be shortened or lengthened (new one) I have a t5 from an 86 camaro in there now does anyone know if my driveshaft i had shortened for the t5 will work? never mind i guess the shaft would be to short because of the tranfer case. I think?
What does the back of the transmission look like? Does it look like a driveshaft will go on it? It should look like this. Notice there is no tail housing at all.
I didn't buy the trans yet so i couldn't tell you. the seller will be sending me casting #s and pics tonight though.
Ok....but you really need to look at it before you buy. The 4x4 has a transfer case bolted to the back of the transmission, and the output shaft in the transmission is shorter, to work with the transfer case. Good luck
cool thanks for the help i appreciate if i didn't ask i probly would have bought something that i couldn't use. If this isn't what i need. I will probly search the junkyards for a 2wd version.
The answer to the question is no. As Jim so aptly said above you need to take the trans apart and put the two wheel drive tail shaft and extension housing on it when you put it back together. That isn't a big deal if you are having the trans redone anyhow but can be a big job for a guy who doesn't do trans work on a regular basis. The tail shaft on the 4x4 trans is a lot shorter than one on a two wheel drive trans. which might be good if you were really needing to shorten things up and had the facilities to fabricate a new rear extension housing. when I get dressed I'll go take a photo of a two wheel "short" turbo 400 tail shaft and you should be able to figure out the difference. The trans case is the same though.
Listen to what Squirrel is saying. It wont work unless you completely disassemble it and install a new output shaft and a tail housing. That means gutting the tranny, and reassembling.
If you can get the 4x4 trans for under $100, it would probably be worth it. I'd want to rebuild any used transmission I get anyways, and converting it to 2wd is not a very big deal if you are rebuilding it.
does anyone know up to what year the transmission must be out of? Or will any thm400 from any year work on sbc or bbc? I am not yet fully decided on the th400 may go with a 700r4 or 200r4 depending on what i find. I havent decided on engine yet either a 427 L88 500hp or i will build a 350 with around 350-400hp
I should be able to probably get it for about 75 bucks. I just didn't plan on getting it rebuilt if i get one. If this is not a 2wd i will see if i can find a 2wd if not i might just get this one.
I gave one of those 4x 400s to a friend as I had no use for it. I believe the spline count was the same as the 2x but shorter. I did see a drum type trans brake fitted to one using the 4x output and a machined shorty output housing with a roller bearing and seal, worked well for a sandrail.
The parking brake version is probably from a motorhome or step van. You should be able to use pretty much any Chevy th400 from a 2 wheel drive, I think they were made up to around 1990 or so. a word of advice...don't pay more than $100 for a used automatic transmission, unless it comes with a written warranty. I've taken apart plenty of "good used" transmissions that needed to be rebuilt...there is no way to tell what condition it's in without taking it apart, unless it's obviously burned up.
thanks for the advise. I was also looking at a 200r4 that was rebuilt but i am not sure if it will handle the 500hp if i get the L88
Ok I got dressed and ran outside camera in hand. You would need these two pieces out of a short tailshaft turbo 400 Yep the tail shaft holds a lot of the innards of the trans. When hunting for a tail shaft or trans there are some differences. There is the short shaft/extension housing one that is on the right in this photo The trans is actually out of a Cad Seville but the tail shaft is correct. The trans on the left is a "long tail shaft Chevy" transmission with the Chevy bolt pattern on the bell housing. Then there is the no way it will fit in there extra long one that is usually only on Cadillacs which is way too long for most any setup anyhow. A good trans guy can probably swap out the tailshafts in an hour and have you ready to go with just the two parts you need and a set of gaskets. But that would depend on if you got the trans for a right price to begin with.
sort of...if you remove the snap ring at the back of the planetary housing, you'll find that the tail shaft is pretty short.
I had a 1983 Chev 1 ton 4x4 that had a 205 gear drive transfer case in it. I think I read that they made two different adaptors to mate this to the transfer case but with the one I had I simply removed the short aluminum tailstock from a 2wd trans and bolted into the truck. I had a friend who also did this to adapt an Oldsmobile 455 into a 4wd chassis by using an Olds car turbo 400. Double check lengths before changing out the output shaft. You might only need to bolt on a tailstock. As for your question about upshifting from first, this will work on a stock 400 turbo but I think a lot of shift kits stop this from happening.
What he says is right, it depends on what transfer case it was put on. There is a late 60's variant used in Jeeps that you can do the same thing, just put the short tail on and a yoke and go, although the yoke is not that easy to find for the spline count on it.
I don't know if it's like an air shifter, but some of them do like to shift by themselves into second, evn if you leave the shifter in 1. You can grind off a land on one of the shift valves and plug a hole in the valve body to prevent it.
No, it just lets you hold the transmission in first gear as long as you want, so you can shift when you want. For example, I shift my 55 at 6000 rpm by holding the shifter in first. The trans would want to shift at 4500 if I had not modified it. A full manual transmission will always stay in the gear that you select. A normal shift automatic will stay in a lower gear if you have the shifter in a lower gear, but will upshift automatically if you leave it in D. It will also shift automatically from first to second if you leave it in 2.
I think I understand the modification will give you manual control in first and second to hold it at any rpm without up or downshifting on its own. But you can still pop it in "D" and have a full automatic. Am I right?
Can you explain more on how to do this modification if you pm me or something. Would you have any pictures or diagrams on how to do this? Thanks
It's included in any decent shift kit. I think it's also detailed in the Ron Sessions book about the TH400. You'll probably want to get the book if you're going to mess with these transmissions.
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