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Thinking of a diff. tranny

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by MudFrog, Oct 12, 2000.

  1. MudFrog

    MudFrog 1/2 ton status

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    I have an 89 blazer, 350 TBI, 700R4, and NP241. My question is I'm thinking of going to a diff. transmission simply because I never use OD and my past experiences have proved the 700R4 to be weak. Would a TH400, or TH350 come close at all to bolting right up? I'm assuming no, so what kind of mods will have to be made. Is there any mods I can make to my 700R4 to make it as tuff as a TH400? Or should I just switch out with a diff. tranny? Thanks for the input guys.

    89 K5 Silverado
    http://mudfrog.coloradok5.com
     
  2. ken

    ken 1/2 ton status

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    A TH400 was optional in the 3/4 ton Suburbans of the era. You could get a 400, although the output is 32 spline, compared to your 700s 27 spline, thus the input of the 241 will need to be changed to accomodate. Back in the eighties there were companies that sold conversion kits to replace the weak 700s with TH400s. I don't know if they're still in business or not, but as I remember the kit was under $200.

    ken
     
  3. chad

    chad Registered Member

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    Hey I have a strong TH350 in my 79 and I would like to have a 700 with OD because I do a lot of highway driving, where are you located? How many miles on yours? and for anybody, what kits would we need to swap??

    [​IMG]
    Cruisin Taz in a 79!
    Chad
     
  4. Goose

    Goose 1/2 ton status

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    From what I've read on this board, I the change would be quite costly. If you switched you would more than likely change t-cases also. The th400 and th350 will not bolt up so you might as well swith from an aluminum t-case(np241) to a cast iron one. This would also necessitate different drive shafts. Also, the 700r4 has a lower first gear which would make you loose some zip off the line. The conversion would be costly and you wouldn't really gain anything.(700r4s can be beefed up very well)
    I would spend the money on re-gearing your diffs so that you can use the OD. You would retain the low 1st gear in the tranny plus have an OD for the highway. Best of both worlds.

    Cruisin in my '73.
     
  5. 1HIHUM

    1HIHUM 1/2 ton status

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    I agree with goose. I have a t350 in my 72, but I plan on going to the 700 next year. They offer a much better first gear( better for take off/and slow 4wheelin) than the 350, and can be beefed up to a comparable strength. I would spend the money on beefing the tranny first, then go higher gears in the axles. Then like goose sayed, you have the best of both worlds!
     
  6. Wheels

    Wheels 1/2 ton status

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    Actually you have one of the better 700R4's. There are mod's that you can make to it, clutch packs, Corvette servo, etc. that will make it a lot better. Jet makes a 700R4 and just about any good transmission shop can perform these mods.
     
  7. MudFrog

    MudFrog 1/2 ton status

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    Can anyone give me a list of stuff I could use to beef up the 700R4? I'd prefer to keep it but the one I had in my 85 truck was awful. What did you mean by I have one of the better ones? How much would it typically cost to beef up the 700R4 to be comparable to the TH350 or TH400? Thanks for the help ya'll.

    [​IMG]
    http://mudfrog.coloradok5.com
     
  8. archer

    archer 1/2 ton status

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    There was an article in the last 4x4 power that talked about the mods that Jet made to the 700R4 to create their venerable T-700. It included: a 10 Vane pump rotor,new Billet clutch convertor torque valve,improved pressure regulator assembly,replacing single stock priming spring with two springs,more (specific) holes in the transfer plate (for faster fluid dispersal), a corvette servo piston, and a nine gear third/fourth clutch pack. Sounds like a piece of cake to me!...............Not. That's what it takes though, and this is an awesome tranny.

    "who dares wins"
     
  9. 86blazin4x4

    86blazin4x4 Registered Member

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    I had a guy build me a 700R4 for my 86. He used a 700R4 from a 91, he was saying that they were built a little better plus like mentioned above, he put different plates and clutches in it. I have it behind a mild built 454 and not a single problem with it. I have it in for two years now. Good luck
     

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