How To Figure Out Rear Gears

Discussion in 'GM Powertrain' started by MTM, Dec 6, 2011.

  1. MTM

    MTM Rockstar ROTM Winner 100 Posts

    Just want to know how to figure out what rear gears my truck has. So any input would be great
     
  2. 99'HEARTBEAT

    99'HEARTBEAT Epic Member Staff Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    Inside your Glove Box is a White Sticker, which is your.....Service Parts ID Tag.....and on it you will see your Trucks Vin Number # and Series of Letters and Numbers......those are RPO Codes which stands for.....Regular Production Options.....In short what your Truck came with from the Factory.

    To find out which Gears you have, you will be looking for the one Following,
    GU5........3.23
    GU6........3.42
    GT4........3.73
    GT5........4.10

    and if you see.......G80 that is the AXLE POSI-TRACTION, LIMITED SLIP
     
  3. MTM

    MTM Rockstar ROTM Winner 100 Posts

    Found it i have 4:10's. Do you know where i could find gears for a gear swap?
     
  4. kburb

    kburb Rockstar ROTM Winner 100 Posts

    East Coast Gear Supply, Randy's Ring and Pinion, Drivetrain warehouse and 4wheel parts. Hit up local race shops they can also get you gear and either hook up with the install or somebody who can if you go the mail order route
     
  5. aloxdaddy99

    aloxdaddy99 Rockstar 3 Years 1000 Posts

    Why would you want to change out the 4.10's? Looking at your sig you are running 33's. I would think that is a good gear for what you have.
    There are a few other ways to find out what you have. Look on the axle, it should be stamped into the housing. This is helpful if you bought the truck used. Another way is to put a mark on one of the rear tires, and drive shaft. Move the truck either forward or backwards. Count the number of rotations the tire turns in one complete revolution of the drive shaft.
     
    Last edited: Dec 7, 2011
  6. MTM

    MTM Rockstar ROTM Winner 100 Posts

    Okay ill have to make some calls and see what i can find.
    [FONT=arial, helvetica, sans-serif]The reason i was thinking about changing gears is to pick up a little fuel mileage. It is not set in stone that changing gears is the best option that's way i wanted everyone's opinion before i did anything. So all suggestions are appreciated.
    [/FONT]
     
  7. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner Gold Member 1000 Posts

    Unless you are driving a whole lot, its gonna take a long time to make up the 1500 dollars or so for the gear change. if you went down you wouldnt want to go much taller than a 3.73 with the 33's. you will start to make the truck work real hard if you went to 3.42 with 33's negating the possible fuel economy benefits of lower rpms at highway speed.
     
  8. MTM

    MTM Rockstar ROTM Winner 100 Posts

    Yea i drive a good amount...I know people wonder why I got the truck but still. I didn't buy it for fuel mileage and I'm still not really that worried about it i would just like to do a few things to help get a little if it's possible. dsfloyd^^^do you think i will pick up a considerable amount of mileage or just 1-2mpg?
     
  9. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner Gold Member 1000 Posts

    I would figure only 1-2 with the gears (other driving techniques might get another 1-2). so thats why I would think at only 1-2 mpg increase it will probalby take a few years to maybe break even. I did something similar with my gears when I lifted mine with 35's. only went to 4.10 from 3.73 because I do mainly highway driving. the lower rpms kept my mileage the same as before it was lifted. but i did lose some acceleration (not important too me), and the truck has to drop to 3rd more to maintain speed up hills (I typically drive 65 which is the speed limit to help with mpg's as well) this still only gets me 12 mpg if I'm lucky but I have the 6.0. If and when I go to more towing I will switch to 4.56 for my truck but it does fine for now with the small amount of towing I do.

    speedo will also need to be calibrated with a gear change. probably off now if it wasnt calibrated after going to 33's
     
  10. MTM

    MTM Rockstar ROTM Winner 100 Posts

    Yeah and I've looked into chips and programers but haven't had any luck on a straight answer if they will help with fuel mileage. Like i said i got the the look i want and now just trying to get a little mileage. I lost a little with the 33's but when i did exhaust i gained what i lost plus some. I also did plugs,wires,cap and rotor and that helped a little. I get 15 now but would like to up that if possible.That's why i wanted some suggestions
     

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