4X4 drive gear ratio!!

Discussion in 'Chevy C/K Truck Forum' started by ICED-OUT-98-LOW-RIDER, Dec 22, 2011.

  1. how can i tell what my gear ratio is and if having different, differentials will mess up transmission, t.case, rear or front differentials?
    need help need to know before i drive it more so i dont mess it up.
  2. SurrealOne

    SurrealOne Former Member ROTM Winner 1000 Posts

    On a 4x4 you need the same ratio front and rear. Assuming no one's modified the truck, check your RPO codes in the glove box and compare to a RPO decoder, online. A quick search on this site will reveal several. You can even search this site to find out what RPO codes are if that's new to you.
  3. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    And if you can't assume no one's rebuilt/replaced an axle (and it sounds like you aren't sure), then you'll have to go out and count rotations. Mark a tire and mark the driveshaft in some way, then rotate the tires through one rotation while counting the number of rotations of the driveshaft. 3 3/4 rotations is a 3.73 gear ratio, 4 and little rotations is 4.11 and so on. Do the same thing front and rear to see if the front and rear have the same ratio.

    Depending on how you do it, you also have to keep in mind what can happen with open diffs and either do something to make sure both wheels on the axle go through one complete rotation, or do it so that only one wheel can rotate. The latter option introduces a factor of 2 (can't remember if it doubles the number of rotations of the driveshaft or cuts them in half -- it should be pretty obvious when you do it, if you do it this way).
  4. i found it out its the gt4 witch is the 3.73 i got the right front end in the truck i basicly had to rebuild the whole front end of this truck including the motor i bought it as a project truck and so far everthing is going smooth and im loving it cuz i know alot about chevys but not alot i just like getting more info and feed back so i know more of what im doing so i dont mess things up so i can do it right the first time every time but yeah i found that out today by a guy wanting to buy the rear axle off my parts truck.

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