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Th350 and TH400... What's the Difference???

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by reddog64, Mar 4, 2001.

  1. reddog64

    reddog64 1/2 ton status

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    Th350 and TH400... What\'s the Difference???

    I got a TH350 in my 78 blazer right now... with a small block 350 and NP203... I got a good TH400 but it's from a 2 wheel drive truck... My buddy says it has a different output shaft, or sumthin and I cant put it in in place of my TH350... is this true??? Is the TH400 better/stronger than the TH350... Is it worth swapping???

    Um... yes officer I know it's too big...
     
  2. prjt_blzr

    prjt_blzr 1/2 ton status

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    Re: Th350 and TH400... What\'s the Difference???

    The 2 wheel drive TH400 case is the same as the 4WD version. The main shaft is different. You can swap out the main shaft to a 4WD version and it will be fine. As for the Tcase that is another problem. The TH400 has a different spline count than the TH350. You can get a mainshaft that has the output part modified to go into a TH350 Tcase but that kind of defeats one of the advantages to using a TH400. It also uses a different plate between the Tcase and the trans. The TH400 to NP203 plate is expensive and difficult to find. The TH400 is also about 2.5" longer than the TH350. This means that you need new driveshafts at $200 a pop or you can retube your old ones for about $100 a pop. You will also need to add an electric kick down switch to the throttle to allow the TH400 to downshift when you put your foot into it. It is worth swapping to the TH400 if you run a big block (I learned the the hard way) or you really thrash your vehicle. If your TH350 is working and you don't have 44's, I don't think the cost is really worth it unless you can get the TH400 Tcase for pocket change. The NP205's are not to hard to come by for this application and they are better than the NP203 and you should also get rid of those wimpy half ton axles..........
     

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