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Rear differentials gear ratio

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Tarek, Apr 11, 2000.

  1. Tarek

    Tarek Newbie

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    Hi all, I need help on the rear differential and front gear ratios. I have newly installed a pinion gear with 15 sprockets with a 41 sprockets on the big gear. I have changed from 11/41 which had more torque. Obviously, I lost torque now and the max speed of the truck was limited to 60 mph not more. I have a GMC Sierra with a 350 engine and a 400 auto transmission. I need help on the optimal gears to install in my differentials. I hardly go off road and need both speed and torque !
     
  2. '73 K5

    '73 K5 1/2 ton status

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    To really be able to help you, we need to know what size tires you are running.

    '73 K5
    Chevy good...Ford bad
     
  3. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Well, you went from a 3.73 ratio to a 2.73 ratio, which definitely explains the loss in power you felt. As mentioned before, let us know what size tires you are running.
     
  4. BB454

    BB454 1/2 ton status

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    I would think that you changed the ratio from 3.73 to 2.73 (as correctly given by the other post) to try and gain some speed. Given the probibility of either 31 or 33's on the wheel side - you are now suffering on the take-off and if you had a manual gearbox, you would be rowing the truck like a boat on the uphill. This was my position some time ago. I changed the 350 engine for a 400 and when this only improved the situation somewhat, the 400 made place for a 454. The truck then had everything that I wanted but at some cost. The suspention had to be upgraded to carry the 454's weight. Other things like driveshafts, cooling etc. makes this the wrong way if you do not intend to offroad the machine. Do not forget the fuel bill the big engine runs up. Somebody must have a better solution for your case. Let's see what comes up.

    BB454
    IF IT DOES NOT HAVE 8 PISTONS - IT'S BROKEN !
     
  5. Goose

    Goose 1/2 ton status

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    FYI: the 'sprockets' are called teeth. Anywho, from what I can tell you want gearing to help out with highway driving and gas mileage. I believe GM put either 3.42 or 3.08 gears in for their trucks used mostly for highway. This is with stock tires (about 31"). This gives the egine engough rpm to be in its power band without lugging it down. If you gear up too much (as it seems you have) the engine is too low in the rpm to have enough power to move the vehicle efficiently. Good Luck

    '73K5,SM465,NP205,33"BFG,4"TuffCountry,3.73:1diffs
    350.4bolt+mods,Warn8000#,Factory skidplates
     

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