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which auto tranny/xcase??

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by arq, Jan 13, 2003.

  1. arq

    arq 1/2 ton status

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    I am currenlty "restoring" a 71 CST blazer. this will be more of a grocery getter, well mabe it'll see some sand at the beach and some curbs at the parking lots. I already have an offroader, so i don't need something indestructible. I want it more as a daily driver or be able to go on road trips with out having to worry about braking/finding parts incase something breaks.

    I have an option of going with the following auto trannies/xcases. I'll probably be running 31-33" tires, 3.08-4.11s, with a 350 engine and a 2" lift. tire diameter depends on the type of tranny and gear ratio.
    1)th350/np205 - 3.08 w/31" or 32"
    2)th400/np205 - 3.73 w/32"
    3)700r/np241 - 4.11 w/32" or 33"

    benefits of (1) is that it's stock, easy to get parts, and practlical with many years of known good service. (2) bit harder to get parts, but more beafier, indestructible, and i know i'll get many hundreds of thousands of miles out of it. (3) what else can i say overdrive, parts are more common and easier to locate.

    before i created an offroader i had a 350/th350/np205/3.08/31s and getting close to 17mpg on the freeway. can anyone from experience tell me how much more would i get with a 700r??

    input very welcome /forums/images/graemlins/smile.gif

    ARQ.
     
  2. Chaz88K5

    Chaz88K5 1/2 ton status

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    700r4 are bad juju...maybe its just me but i killed 3 of em..when i pulled the 4th one out to swap to a manual it was still workin...but never again will i have a auto in my truck...except a th350 or 400
     
  3. Burt4x4

    Burt4x4 3/4 ton status

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    I like the looks of option #2. Option #1 would work too but use 373s /forums/images/graemlins/thumb.gif
     
  4. Roostr84

    Roostr84 1/2 ton status

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    I don't know if it were me investing the money (depending on what you are looking to spend) I would go with the 700 combo. You get a nice low first gear and an overdrive that will drop you final ratio down around 2.8:1 with 4.11's. I know they have a bad rep stock but there are plenty of places that sell modified ones to handle 400-500 ft/lbs of torque or you can get the extra bands and clutches and other parts and do it yourself if you are inclined. Also the lock up convertor is nice on the highway too. But again it all comes down to cost.
     
  5. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Arq,

    I'd look into option #3.....

    Regardless of what the others say, the 700R4 would work fine....(I will remind everyone, this is what Stephen Watson uses in the ORD Jimmy, and Steve Fox uses in UAV!) You have to set up the TV cable correctly, and you want to make sure you don't buy some early-80's turd that doesn't have all the "updates".....but let's be honest, you aren't even going to 'wheel this thing, so even a stock rebuild 700R4 will be fine.

    The 700R4 has the lowest 1st gear of the bunch, and a 30% overdrive....which means you can go 30% deeper on the rearend gears for great around town "oooomph" and still have good highway RPMs.....

    I'll leave the specific RPM calculations to you to do, based on your tire selection, gearing preferences, and preferred highway travel speeds.... /forums/images/graemlins/thumb.gif
     
  6. Chris_T

    Chris_T 1/2 ton status

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    I'll second Greg's opinion. I have a 700R4/NP205 and I really enjoy the 700 over my TH350. It's all in how you use/abuse it. Cooling is a big deal with any auto for long life and it's easy to solve. The 4L60 in my 94 has been badly ignored and still drives like new after 170000 miles
     
  7. Burt4x4

    Burt4x4 3/4 ton status

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    Booooo
    First gen don't like no stinking 700whatever..
    What does he need that low first for?
    heheheh just playin. ARQ ~ so many options makes it confusing buildup.
    It all depends on the three 3s...
    Money
    Time
    reliability

    Tell me again how long the TH350 and 400 slush boxes have been around??? Like FOREVER..... I have never owned a slushbox before but it seams to me thease two are the 'work horses' of the group!!
    Just my .02c
     
  8. 70~K5

    70~K5 1/2 ton status

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    Then theres another option not listed. A 4L80E/NP205 like in some of the late crewcab 1 tons SAS. The strength of a T400 in a 4 spd package. /forums/images/graemlins/thumb.gif
     
  9. RingMaster4x4

    RingMaster4x4 1/2 ton status Premium Member

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    Are those Trasmission computerized?
     
  10. 70~K5

    70~K5 1/2 ton status

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    Yes they are. But get the 454 and the trans etc with the puter and wiring and you're set.
     
  11. 72beater

    72beater 1/2 ton status

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    don't forget the powerglide...just kidding!
     
  12. Roostr84

    Roostr84 1/2 ton status

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    I had thoght of this option before however if this is just a daily driver the 4l80 is a pretty parasitic transimission.
     
  13. Steve_Chin

    Steve_Chin 1/2 ton status

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    Dennis, what about oprion #4, NP205/NV4500? Seems to me like the best of all (of course, I'm prejudiced!).
     
  14. arq

    arq 1/2 ton status

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    thanks for all of the responses. the trannies i have sitting around so cost at this point is not the issue, the moneys been spent already. i know i can get it back if i sell them. I'll probably stick with the th350/np205 running 3.08 with 32".

    the nv4500/np205 would be a sweet combo, just that it's an expensive one. how is that setup running, Steve?

    ARQ.
     
  15. Steve_Chin

    Steve_Chin 1/2 ton status

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    It runs great, Dennis. It shifts slicker than the transaxle in my Fiero does.
     
  16. '72brett

    '72brett 1/2 ton status

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    I read the info on your dog, steve. I was wondering what kind of birds you hunt. I dont think a poodle is tall enought to get around for what I hunt. But im sure we have 2 completely different landscapes. Please fill me in, I'll be waiting for your reply
     
  17. R72K5

    R72K5 Banned

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    i vote for th350, UNLESS you find a 700r4 thats 88-up and built, anything beofre that are junk, for real, 8 was major upgrade year, addition of aux valve body and 10 vane pump and so forth alot better stuff in them, personally i woulndt run a 700 with tall tires and 3.08 or higher ratio like 2.73, that ratio and taller tires are murder on trannies., 3.73 or 4.10 would be ultimate with 700r4 30' some tall tires, but then everyone has their own ideas and opinions, i am going by what i have personally seen happen to ppl because of not addsing up factors like ratios and tire size in their drivetrain choosing plans,,

    personally i believe i am pushing it wih my almost 30" tires on my 81 C10 with th350 and 2.73, lower RPM lugging/torquing the tranny, bad..
     
  18. Chris_T

    Chris_T 1/2 ton status

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    I missed the second part of your Question about mileage on the 700R4. My experience is that highway mileage increases a bit, but only with the proper gearing.

    I started with a TH350/NP205, 3.73's, 35" tires 10-12 mpg highway.

    I went to a 700R4/NP205, 3.73's, 35's and the mileage didn't get any better since in OD the revs weren't high enough to maintain cruising speed on any sort of incline. As soon as I hit a headwind or a hill it would want to go into 3rd - I tended to drive in 3rd and still had the 10-12 mpg. (If you think about it, OD and 3.73 was like a 2.60 gear ratio with a TH350 .. way too low for 35's)

    I swapped the 3.73's for 4.56's. What a major bonus in all around driveability. City mileage didn't seem to go down (didn't keep any numbers), I can drive in OD in the city no problem without it shifiting in and out continually. Highway mileage improved from 10-12 to 12-14 mpg. 2 mpg probably won't pay for the swap for years and years (I figured that out on the old Blazer world page once - it really doesn't make financial sense to spend big $$'s on an OD just for mileage) but the driveability is much nicer. I still feel like I could have gone for lower axle gears though - 4.88s might have been a good choice for 35's.
     

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