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Gear swap or Tranny Swap?

Discussion in 'The Garage' started by hunterguy86, Feb 19, 2007.

  1. hunterguy86

    hunterguy86 1/2 ton status

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    Location:
    San Marcos, Texas
    I have a 700R4 and an NP208 on my 86 K5. I am running 35's and have 3.73 gears.

    I really want to do an SM465 NP 205 swap to the truck and want to run 37's.

    I was thinking that if I kept my 3.73's It would still do ok offroad because of the granny gear of the sm465 and would still be ok on hwy because the taller tires would give me a lower RPM on the highway that it would if I ran 35's.

    I think the sm465 would give me the same mileage as my 700 because overdrive is useless anyway. It hunts between d and od so much that I dont even use it so I dont burn up the tranny.

    What do yall think? Would my gas mileage stay about the same if I ran an sm465 and 37's vs a 700 and 35's?
     
  2. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    SM465 with 37s, and 3.73 gears is pretty much a perfect 2200 rpm at 65 mph.

    700r4 with 35s and 3.73 gears is still very decent at about 2400 rpm at 65 mph (out of O/D) In O/D, you'd be at like 1700 rpm at 65 mph, which is just majorly lugging your engine.

    That, and a 700r4 won't live long pushing 37s. I'd do the SM465 swap myself. I did the same thing with my truck, and will never go back...
     
  3. Chevy305

    Chevy305 6 Lug 14bsf Status Premium Member GMOTM Winner

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  4. hunterguy86

    hunterguy86 1/2 ton status

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    Thanks for the input. Thats about what I figured the RPM would be like.

    How much do you have into your sm 465 swap?

    Im trying to build a parts list so that way I can hopefully get it done all in one weekend this summer.
     
  5. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    About $200 or so...

    I got a free SM465/205 combo with driveshafts. Found the SM465 needed an overhaul, so I spent about 100 dollars doing so. I only had to replace the sintered bushings on the mainshaft and my syncros, the rest was in good shape, and re-usable.

    I then got a set of hydro pedals, hydro bellhousing, and the master cylinder / slave cylinder / line for another 60 dollars at the wreckers.

    I then had to buy a mount for the transmission, tranny hump and a bunch of bolts etc which brought me to about 200 bucks or so.

    Only took me an afternoon to install the whole setup. Goes pretty easy if you know what you are doing :)
     
  6. hunterguy86

    hunterguy86 1/2 ton status

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    I've removed and installed trannys several times. I think installing the tranny/tcase is going to be easy. The hard part is going to be installing the pedal and stuff.

    I was wondering, is the slip yoke on the driveshaft the same between and np 208 and an np 205?
     
  7. drop the hammer

    drop the hammer 1/2 ton status

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    I just got myself a 465 and fixed yoke 205 from an 80 1 ton to replace my 700 and 208 combo in my '83 K-5. Now I just gotta install it. I just like the toughness of that combo, you could roll the 465 down a hill and shoot it and it would still work. Also you cant beat the gear driven cast iron durability of a 205, I had one behind a T-18 4speed granny in my F-250 that I beat the cr@p out of and it never complained. You want something tougher your only option is the Atlas
     
  8. u2slow

    u2slow 1/2 ton status

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    Location:
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    $150 for bell & pedals
    $150 for new master, slave, & line
    $50 for flywheel machining

    Other items I traded for work
    - fork & ballstud
    - driveshaft lengthening

    Stuff I already had kicking around:
    - trans hump
    - SM465 trans
    - clutch
    - flywheel
     

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