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Differences between a TH350, TH400, 700R?

Discussion in 'The Garage' started by zakk, Mar 9, 2003.

  1. zakk

    zakk 1/2 ton status

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    What I know:

    TH350: clutches and 4" shorter than a TH400. NP 203 & 205 models

    TH400: strongest GM auto tranny of its era. NP 203, 205, 208 models

    700R: Lowest 1st gear, post-'89 are more desireable, OD, TV cable

    what am I missing? also what makes the TH400 stonger than the TH350?

    TIA!
     
  2. bablazer73

    bablazer73 1/2 ton status

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    the Th400 uses a larger sprag, and larger drums/clutches. The shafts are also larger. But you can get better pieces for the th350 from several tranny places. The sprag is a week link in these tranny's.
     
  3. tarussell

    tarussell 1/2 ton status

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    In response to what makes a TH400 stronger there a lots of things , a few that come to mind are the ability to increase torque capacity of the clutch packs by using an extra deep ( or shallow ) clutch drum and having a total of six frictions and six steels. The planetary's are stronger than the TH700 & TH350 and you could use the TH475 straight cut gears for a serious upgrade if you don't mind a little whine from the tranny. Also as mentioned above the shafts are larger as well.
    Don't forget about the H.D. cases with the thicker bell housing castings ( TH350's and TH700s also have this offered in 4WD cases too ).
    IMHO you can build a TH700/TH350 to handle a fair amount of power but a equivilant (sp) TH400 should be able to handle much more power and have a stouter service factor .
     
  4. MJB774X

    MJB774X 1/2 ton status

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    the center support on the 400 has a bolt going to it to keep it from banging against the case where as the 350 just has a small funny horse shoe looking spring that puts tension on the hub against the case in turn wearing out the case from the hub banging against the case they do make small steel shims to put in if the case is worn, or to prevent it from wearing, but why go through the hassle, just run a 400
     
  5. ntaj*ep

    ntaj*ep 1/2 ton status

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    Here is my 2 cents worth of knowlage.
    The TH350 uses the same tail housing bolt pattern as the 700r4 yet are about 3/4 to 1" shorter. The TH400 and the 700r4 are the same length yet have diffrent tail housing bolt patterns. these units are avail. in a 4wd housing which is a thicker housing. The spline count is the same for the TH350 & 700r4. However the length varys. /forums/images/graemlins/thumb.gif
    I will leave my opinion out of this as you asked for fact.
     
  6. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Well you already know my position on the TH400, but I'll throw it in for the masses.

    All around strongest auto you can get for the money invested. Match upgrades dollar for dollar and the 400 will leave the others in the dust. I'm running a TH400 and NP205 with 4.56 and 42s on extreme trails where I have to slip the converter something terrible, and that's often in temps over 100 ambient. It shows no signs of fatigue yet. I do have a big cooler but, I don’t think there is another tranny out there that could survive that abuse, including the 465 which would likely have smoked a clutch (and stalled many an engine) by now if used for creepy-crawling like I do with my crawl ratio...

    But, alas, I’m moving away from a TH400 due to the problem finding parts. NP205s for them are hard to find and can be pricey. But just TRY to find a 203 for one. Only made in 78-79 and only by special order (optional full time) on 1 tons… I could try adapting a different adapter to work, or I could persist and find the right 203 and adapter, but then what happens when/if I break one? One of the local guys just broke the 203 adapter on his doubler in the last few weeks. <shrug> I’m just going to the more plentiful TH350/203 and I’ll be building the TH350 with HD parts. Should be ok with the doubler behind it, and I’ll probably put the 400/205 in my son’s truck (when he gets one)…
     
  7. Rusty68

    Rusty68 1/2 ton status

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    I have the TH475 trans in mine with a Allison converter. Compared to the 400 in my other truck its just a tad noisy. But only until you get up in speed. But its not that bad. When I had it built, the tranny guy told me break it if you can!! hahaha, Anyways he is running the same trans in his mud racer. Has been in there for 2 years with no problems. He converted from the 465 because he kept stripping the coupler between the trans and case. Guess that didnt really say much towards your question though. /forums/images/graemlins/truck.gif
     
  8. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    In addition to the heavy duty sprag for "110% more torque handling capability"...
    You can also order deeper gearsets for the TH400 1st and 2nd gears in the Jeg's catalog... I think it's about $300.

    Also if you swapped in a longer tranny (from a 350 to a 400 or 700) you could move the engine forewards instead of moving the tranny/tcase back and having to re-do both driveshafts.
     
  9. Sample

    Sample 1/2 ton status

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    Wow, I didn't know that the 400/203 combo was so rare. I jusst picked up this combo from my father-in-law's '78 he is parting out. He has told me that the 400 was recently rebuilt with a shift kit too.

    I am trying to get this swapped in place of my 700/208 combo that died on my recently. I was just looking for any cheap replacement to get my K5 back on the road again, this happened to be a great choice since it was FREE.

    Now I just have to pull my 700/208 and put this one in, along with the crossmember. I am not sure what needs to be done with the drive shafts yet.
     
  10. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Arrrgghhh /forums/images/graemlins/angryfire.gif

    LOL! Just kidding. /forums/images/graemlins/laugh.gif Fantastic luck, you got the good stuff, now your set for a doubler some day... And yet again I'm "SOL"... /forums/images/graemlins/crazy.gif
     
  11. 70~K5

    70~K5 1/2 ton status

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    [ QUOTE ]
    Arrrgghhh /forums/images/graemlins/angryfire.gif

    LOL! Just kidding. /forums/images/graemlins/laugh.gif Fantastic luck, you got the good stuff, now your set for a doubler some day... And yet again I'm "SOL"... /forums/images/graemlins/crazy.gif

    [/ QUOTE ]
    Russ B&M built a TH400 with a output shaft to match a TH350 as a replacement that used the TH350 adapter and TC. If you could get the output shaft put in your TH400 you could use the cheap TH350 203s.
     
  12. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    /forums/images/graemlins/confused.gif
    How could it use the TH350 adapter? It has 4 holes on a square pattern, the TH400 has 6 in a hex... The shaft I can understand, but I'm confused on the "use a Th350 adapter", that's the piece I was most concerned about breaking. /forums/images/graemlins/ears.gif /forums/images/graemlins/laugh.gif
     
  13. bablazer73

    bablazer73 1/2 ton status

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    Some of the later model 400's also came with the smaller 350 style output shafts when they were mated to a 208 case. I have 2 of those trannys.
     
  14. 70~K5

    70~K5 1/2 ton status

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    I don't know if they still list it, but 10 years ago B&M made a TH400 that would bolt in place of a TH350. According to them the only thing needed to be changed when using it was your driveshaft lenghts. I never bothered to use one as my 77K20 was totaled by a drunk driver before the TH350 died after being rebuilt. But that was going to be my next step if it didn't hold up.
     

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