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Should I stay TH350 or go TH400????

Discussion in 'The Garage' started by SUPER'BURB, Jun 16, 2005.

  1. SUPER'BURB

    SUPER'BURB 1/2 ton status

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    I blew my TH350 and have to decide if I want to stick with that set up or go with a TH400 :confused: .

    I know the gearing is a bit differant but I'm going to change ring and pinions any way.

    What would you guys do???

    Whats the price differance???

    Any thoughts or suggestions are appreciated, :waytogo: thanks.
     
  2. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Bear in mind you need to swap other stuff beforehand also . Both tranny's have different output shaft splines , and different adapters .

    Personally I would run another th350 .
     
  3. mudslinger99

    mudslinger99 1/2 ton status

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    I'm guessing this is for a Suburban because of the name but what year is it ? What drivetrain are you running ? What is it used for trail,mud daily driver ? Some people might even say 700r4 depending if you want overdrive and what you are going to do with it..

    With that added info I'm sure a few people here could tell you exactly what adapters and things you will need to make the swap..

    If you are having breakage due to a strength issue then maybe a 400 is a good idea... If it just quit from mileage/old age then I would rebuild the 350 and put it back in.. You can have it rebuilt for a fairly decent price or you can do it yourself depending on your mechanical know how.. Or you can find a 350 ready to bolt in pretty easy to.. They are actually easier to find then a 400..
     
  4. SUPER'BURB

    SUPER'BURB 1/2 ton status

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    It's a 73 Burb with a Dana44 front, ff14 rear and 4:10 gears. I drive about 100 miles a day. But I don't care about mileage as my company pays for it. Besides that I tow (usually less than 6K lbs.) about once a month and play in the mud every weekend from november thru may.

    Just for a bit of knowledg on my situation I run a 350 making about 400 horse and 400 lb ft of torque.

    Thanks again, you guys ROCK :saweet: :saweet: !!!!!
     
  5. SUPER'BURB

    SUPER'BURB 1/2 ton status

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    If I go 400 can't I order one with the correct output shaft?

    Also how difficult is it to rebuild a tranny? I have done 3 complete motors and many partial motor builds. Trannys have alway been somthing of a veiled thing to me I sorrta know how they work but never had the time or inclination to tear one apart to see exactly.
     
    Last edited: Jun 17, 2005
  6. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    I haven't really searched , but I don't remember ever seeing a 27 spline th400 .
    The input on the case is changed easier and quicker .
     
  7. SUPER'BURB

    SUPER'BURB 1/2 ton status

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    Are you meaning an adapter or tearing apart the T-case? :confused:
     
  8. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Th400 will have a 32 spline output in all versions, so the input on the tcase will have to be changed. And the output is different for 203, 205, and 208/241 as is the adapter. Th400 is longer, heavier, has a higher low gear, and more parasitic power loss, but is much stronger. Th350 can be a very strong trans when built right, lower first is always a plus as is less parasitic loss and you get the benefits of less weight and shorter package. This is my current preference for my rock buggy. 700R4 has a MUCH better (lower) low gear plus the benefit of OD. It is much like the Th350 except longer and really needs a GOOD performance build to live behind a 400/400 (assuming those are real dyno numbers, very few streetable (for a 4x4 truck) 350s make those numbers) if you romp on it AND tow. It also requires some tweaks to the output shaft to go In front of 203 or 205, but would suggest the 208/241 is generally a better choice anyway due to the lower low range. 700R4 with 208/241 is often called the "poor boy's doubler" due to the nice compound low.
     
  9. 79chevyk10

    79chevyk10 1/2 ton status

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    No such thing as a 27 spline on the output shaft of a th400, cooler lines are different and its a longer trans, so many things have to be modified. That being said the th350 is plenty of trans for any small block if build correctly, and there are tons of hop up items available though people like ATI to handle the power.
    If I were you I'd keep the th350 because the gains may not out wieght the work and money. That way you can use the money other mods. IMO.
     
  10. SUPER'BURB

    SUPER'BURB 1/2 ton status

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    Thank you for the input I think I am leaning towards the 350 now, my biggest concern is the power the Dyno #'s on my 350 are actually 403 HP and 393 FT LB of torque. With that type of power can I get a TH350 to live while driving it alot? I also have a pretty heavy foot when I play.

    Can I as a reasonably mechanicaly inclined person build a TH350 at home?
     
  11. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Sure, a Th350 can live well over 400hp with simple shift kit, upgraded sprag, and a few other tweaks. Probably does not even need upgraded clutch/steel/drums as long as you don't drag race or pull heavy and hard. Since that is likely a high rpm motor (based on hp/tq spread) you'll need a higher stall converter than most of us use and VERY good cooling, particularly for towing.

    Get Ron Session's Th350 book for all the gritty details.
     
  12. SUPER'BURB

    SUPER'BURB 1/2 ton status

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    Thanks BadDog

    You saved me hard earned $$$$$$$ :grin:

    And yes the motor is kinda high RPM.
     
  13. 79chevyk10

    79chevyk10 1/2 ton status

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    You can make the trans live for sure. You do need some special tools to build the trans correctly but I don't see why not. TH350's are pretty easy to build.
     
  14. REDCRO_REDNECK

    REDCRO_REDNECK 1/2 ton status

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    Teckpak fitzall makes one. the 400 tail shafts that are machined and have a 350 spline pressed and welding to make the shaft.
     
  15. mr_clean

    mr_clean 1/2 ton status

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    Also to note, if you decided to change the input shaft on the tcase, if the case is a 205 I believe you would have to have the case machined out to take the bigger bearing of the 32 spline input.

    I don't know if that is necessary with a 203 case or not.
     
  16. sweetk30

    sweetk30 professional hooker Premium Member

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    th350 held up fine in my old truck and still going. 38 tsl tires and built 400 sbc 1ton axles 4.10 gears.


    as for 27 spline th400 factory. yes thay did. i have one . its a 2x4 long tail setup out of a truck that was 4.3 v6 setup . but this will be to long for your needs.
     
  17. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    What I meant was that 4x4 th400s all had 32 spline outputs. 2WD is not relevant since they won't work with any of the existing case adapters.
     
  18. sweetk30

    sweetk30 professional hooker Premium Member

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    i know that just pickin.:D :grin: :cool1:
     
  19. wy4tt

    wy4tt 1/2 ton status

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    I was wondering the same thing when I switched over to 1 ton parts. The tranny guy told me I'd be fine with a nicely built TH350, shift kit, and a big cooler. From what he says, temperature is the big enemy of the 350. So that's what I did. I've got a 330hp 380 ft/lbs 350 in it, 37s, 4.56s.
     
  20. mudslinger99

    mudslinger99 1/2 ton status

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    See I told you with a little more info you could find the answers to your questions and get plenty of help along the way :D

    On the tranny issue it sounds like you will be fine with the 350 tranny if you have it built right.. I have seen plenty of trucks with your same set up last a long time with plenty of abuse.. By rebuilding the 350 tranny you have now will cost alot less then changing over to a 400 that sounds like you wont see much benifit from... Good luck

    Here is a link to the Ron Sessions 350 and 400 turbo transmissions books that were mentioned..

    http://www.amazon.com/exec/obidos/t...f=sr_1_2/103-0878061-0611068?v=glance&s=books
     

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