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Gearing..one more time :)

Discussion in 'The Garage' started by Tire, May 3, 2007.

  1. Tire

    Tire Registered Member

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    I have some questions if anyone would care to take the time to answer them. My 79 k5 building basically from scratch now has brand new 350 motor goes to origonal 350 turbo and np203, and the same 10 bolt front 12 bolt rear from factory with 3.18 gears. Interior stripped and bedlined. I will be running 37" goodyear mt's on 16.5 6 lug wheels ( those wheels are hard to find btw I have the tires but have yet to get the wheels). My question is are 4.56 gears to much for this truck to run 65-70 hwy are are they just right (has anyone tried). All my calculations tell me i am looking at running 2700 rpm and 65 on the hwy with 4.56 gears that seems a little high. I can drop this to 2450-2500 rpm with 4.11 gears, but how much will my low end power suffer? I am building it for some serious trials but i have radial tires for a reason i will have this on the street too, and that means long drives to the trails using the hwy. I know it's been asked before and answered but a few more opinions make all the difference.
     
  2. Mudstud

    Mudstud 1/2 ton status

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    Welcome, hmmm where to start. First off, IMO, 4.56 is a good choice if you are concerned about RPMs at highway speed. If not the deeper the gear the better (without loosing strength in the pinion). Anyways, If you are talking serious offroader running 16.5 wheel/tire combo you may want to invest in some type of beadlock. It doesn't take much for a 16.5 tire to come off teh rim, potentially ruining the expensive tire. Perhaps recentered Hummer rims would be a cheaper road then replacing/trading/selling your tires. I have afriend in Mephis that has a set of 8 bolt hummer rims with 6 lug centers he may be getting rid of. The Hummer wheels have dual beadlock. Food for thought. Keep posting questions. A serious off roader focuses on 3 main things- gears, lockers and tires- not necessarily in that order.
     
  3. 1977k5

    1977k5 3/4 ton status Vendor

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    I have 4.56's on 37's and the motor spins too high for me, ~3000 RPM @ 70mph. And I have a manual, yours would be higher than that (because autos slip).

    I don't plan on changing gears when I go to 42's. I'm not really low on power though.
     
  4. huntingaddict

    huntingaddict Registered Member

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    It really does depend on power. Guys with anemic 4 bangers have to run super deep gears because they have no power. I run 3.73's with 35's and don't plan on changing when I go to 37-38's. My truck ran better with 3.08's than a guy I knew's truck that had 3.73's because he had a stock 305 motor. I'm looking at going to 37's just to get the cruise rpm back down a bit. It has plenty of power to pull them. So I guess my answer is if you have some power the gear is not so critical.
     
  5. Chrisblazzer89

    Chrisblazzer89 1/2 ton status

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    OK these 3 thing dont add up to good.

    10b & 12b + 37s + Serious trails = lots of broken parts you need to go 3/4 ton or even 1 ton for Serious stuff.

    Btw 4.56s sound good
     
  6. Tire

    Tire Registered Member

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    Ok thanks for your help guys. I am aware that i could easily shell those diffs but they ain't broke yet :wink1: . and parts can be taken out and sold just as easily as they are put in. When i get a sweet deal on some already geared 3/4 or 1 ton axles I had planned on the swap. i'll run the 4.56's just b/c i want the low end more. please let me know a price on those hummer wheels. thanks guys!
     

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