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tranny question

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by ed rex, Dec 10, 2001.

  1. ed rex

    ed rex Registered Member

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    So, swapped out the 3.73 gears on my 14bolt FF w/detroit to 4.56 last week. Mated to a BB454 via turbo 350 tranny/new process x-fer. Now, about 200 hwy 'foothill' miles and several mud pits later, the tranny is starting to slip and chatter. Could this be a result of a tranny that was wearing thin and the 4.56 gears just accelerated the inevitable? What does one do to remedy? Is this a tranny rebuild situation or is there something a 'weekend mechanic' such as myself can address? If rebuild/replace is required, what would be the optimum replacement given the components listed above? Thought I heard something somewhere that said the TH400 is not a good tranny for 4WD apps. True? False?

    Thanks!

    Ed
     
  2. arq

    arq 1/2 ton status

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    reason that the 350 may be better than the 400 is the lower 1st gear ratio in the 350. as for the slipage, are you using a tranny cooler?? it may have been that when your tranny was rebuilt the oil pump may have been out of spec. I am going through the same. i hate auto, i'm just waiting for it to die so i can through my sm465 in there :-)

    ARQ.

    offroad baja!!!
    72 4x4 CST Blazer
    71 4x4 CST Blazer
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  3. 82GMC

    82GMC 1/2 ton status

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    <blockquote><font class="small">In reply to:</font><hr>

    Thought I heard something somewhere that said the TH400 is not a good tranny for 4WD apps. True? False?

    <hr></blockquote>

    Most certainly FALSE! TH400's came stock in a ton of GM's 4x4's, And are stronger than TH350's. It prolly is rebuild time on your tranny, I whould swap it for the TH400 if I were you though.It'll hold up to the 454 better. I don't see why the gears whould have anything to do with your tranny problems. Puttin gin those lower gears, Whould put less strain on the tranny, Because it whouldn't have to work as hard, (And neither whould the engine) To move the tires.

    I am the hunter Who live's in the darkness, And grows through your fears...... And you are the hunted.
     
  4. ed rex

    ed rex Registered Member

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    Thanks for the tips. Since Christmas is over, I find myself with enough 'winfall' to just replace the TH350. Don't want to get carried away, but would like to upgrade to a 400. I plan to do the removal and re-install myself. Questions are: Is the 400 a direct bolt in replacement or are there hoops to jump through to get it mated up correctly? I know on the engine side it'll just bolt, but what about the xfer case side? (NP205). I think I read that the 400 is longer. If indeed this is true, is it longer to where I would have to have my rear shaft shortened? What about the crossmember? Are the 400 mount spots identical as the 350's? What about the linkage and the steering column? 1, 2, drive still applicable?

    I was just thinking I would remove the 350, haul it down to a reputable tranny shop and tel them I need a 400 that would replace it. Sound thinking? Now, what about shift kits, stall converters, and the like? Should I 'order up' a 400 with anything special? Keeping in mind the 454/4.56 combo, what TH400 tranny configuration would be best suited?

    Finally, am I in for a rough experience? Or is this really a 'no biggie'?

    Thanks!!!
     
  5. Triaged

    Triaged 1/2 ton status

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    I don't know about the length but you will need:
    TH400 to NP205 adapter
    New input shaft for NP205
    Have case machined to fir new input shaft (it is a female shaft and has a larger OD and larger bearing

    '71 Blazer CST w/ a 400sbc, 4" lift, 36" Supper Swampers, and alot of rust
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