OT: Change TH350 to TH400

TH350 is shorter than a TH400, so you would need to shorten the DS. You would need to move the cross member back I believe 3.5". You would also need to get your head checked, because the TH400 is a problematic transmission that chews it's self up internally (literally, and NOT just the clutches) where as the TH350 can be built into an unbreakable monstrosity and the TH700R4 isn't far off.

GMC Gremlin

Ya got it backwards bud, the TH400 is a much stronger transmission than the TH350 or the TH700R4. How many street/strip machines run 350's as opposed to 400's?

He'll also need to wire-in a kickdown as the TH400 has an electric kickdown whereas the TH350 has a cable-actuated kickdown.

Doc

I just ran a google search and could not find it. But I swear I remember a post from Gary about how there is a shaft within the TH400 that can chew out it's carrier & the case. I was able to find one problem from gary: "the 400, while sturdy, requires a LOT more care in rebuilding, especially older units...........center support-to-case wear will kill the intermediate and direct clutches in short order if not addressed properly, and end-play is critical"

But I also remember him bashing it (quite severely?). Guess it's just me that remembers him. However I have heard allot of people say that it is a great tranny. But in my defense, allot of people say that K&N is great. And insist that a "bigga intake" is essential....

GMC Gremlin

transmission

All of the 60's and 70's era GM muscle cars that I owned that were automatic all had the TH400 in them. That transmission can take some serious abuse trust me. ;-)

1968 Pontiac GTO 400 Cu In 350 HP 1969 Olds 442 400 Cu In 350 HP 1971 Chevy Nova 350 Cu In 330 HP

Brian

Look at it this way...................put a bone-stock TH350 behind a 454 and watch it grenade quite quickly. Put a bone stock TH400 behind a 454 and it'll run forever. The TH350 does require less power to drive it, so it is a more efficient means of getting flywheel power to the rear wheels.

I remember the post to which you are referring; he wasn't really bashing it, just pointing out the one major flaw in its design. Hell, if I worked on blown up trannies all day I'd likely have some nasty things to say about them as well!

Doc

I just also remember him saying it was better to build a TH350 up than a TH400 because of those. Just my $0.02 DEFINITELY not a "tranny" guy!

GMC Gremlin

There are some that prefer the TH350 to the TH400 in a racing or performance application. As I've been told that the TH350 has a lower 1st gear than the TH400. And if one wants to they can build the TH350 to be pretty strong. But in stock forms the TH400 is much stronger, probably when both are built up as well.

Brian

In 'stock' (NEW, no case-to-center-support slop, no case lugs chewed up by center support, all bushings in good shape) the 400 is heftier than a 350

However, the torque converter in a stock 400 is pretty 'doggy' (loosely coupled), at least I feel it is

A properly rebuilt 400, if one can find a good case, good center support, wants to replace EVERY bushing in it, pays meticulous attention to end-play (both front and rear, the 400 has two separate end-play adjustments and requires a lot of checking on this), and if you put either a good custom converter in front of it, or use the AT-540 Allison converter for everyday use, it will be marginally better (IMO) than a 350

A 350, on the other hand, can pretty much be tossed together from across the room, mated with the stock '4701' 'truck' converter, and give the 400 a run for its money

a 700 is a 350 with a different arrangement of the gear train, lets you run a higher (numerically) rear gear and still get resonable mileage via OD in

4th

the 700 does REQUIRE the lock-up to be functional, ot it will toast very quickly at highway speeds

Okay. I don't think I have ever gotten this quite right in my head. A TH700R4 has the following gear arrangement:

1-2-3-4 and LOCK UP. And from what you just said, if I choose "3" instead of "OD" my TC still locks up (or should)?

Have you ever heard of or installed the kits that allow you to select any gear in the TH700R4? I've heard of these but I have never really read about them.... couldn't find anything. It is supposed to allow you to choose any gear you want, so if you want to START in fourth - then you can. I always feel that my truck would have allot more "romp" if when I punched the gas, it didn't kick down to first gear or whatever the hell it does (while revving to the moon). If it acted more like a manual....

GMC Gremlin

It's called a manual valve body. Makes it essentially a standard transmission without a clutch and with a torque converter. About $300 for a TH350 or TH400, $400 for a TH700R4 in Jegs or Summit.

Doc

Does it allow automagic operation as well?

GMC Gremlin

some shift 1-2-3-4-L

some do it 1-2-3-L-4

and some early S-10's will even lock up in 2 (and with a 2.8 that makes it a REAL dog)

nope

never tried 'em, probably never will

Some do, some don't, depends on which you buy. Some are 100% manual, some will still give you automatic shifts so long as the gear selector is in the highest gear when you start moving.

Doc

Well the surgeon doesn't have any experience with them, what is your opinion?

GMC Gremlin

I don't have an opinion, never used one!

Doc