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Determining Differential Gear Ratios From the Information Plate
    You can determine what differential gear ratio your Toyota truck or 4Runner came with from the factory by looking at the Information Plate located on either the driver's door jamb or under the hood.  This information tag can be found on Pickups from 1984-1988 and 4Runners from 1984-1989 under the hood on the top center of the firewall right above the engine.  Trucks from 1989-1995 and 4Runners from 1990-1995 have a tag on the driver's door jamb.  Note that this information is only valid if your vehicle still has the factory gears. 

     For the easier method, you will be looking on the tag for the following:

C/TR/A/TM

     In the above, "C" stands for vehicle color, "TR" stands for trim type, "A" stands for axle type, and "TM" stands for transmission type.  Below or to the right of these abbreviations are the codes for each.  It can sometimes be tricky to read the codes as they aren't seperated very well from each other, so make sure not to get them confused.  The different codes are sometimes only seperated by a small space or a bullet.  Look at the third code for "A" and you can determine your ratio from this.  It will consist of four alphanumeric characters--the first being a letter and the last three being numbers.  For example, the axle code for my 1985 Toyota 4x4 is "G292."  This tells me I have 8" differential with a 4.10 ratio and two pinions.  This will make more sense after you look at the charts below.  Most 4x4 axle codes start with a "G," and most 2WD trucks start with an "F."  The 4 digit axle code is actually 3 different parts.  Below is a listing of the different possible codes and their meanings.
Second and Third Digits:
Fourth Digit:
First Digit:

Code     Gear Diameter

  F     =     7.5"
  G     =     8"
  H     =     9"
  J      =     9.25"
  K     =     9.5"
  L     =     10.5"
Number of
Pinions

2
2
4
4
Code

  01
  02
  03
  04
  05
  07
  08
  10
  14
  25
  28
  29
  30
  37
  38
  39
 Gear Ratio

3.30
3.36
3.54
3.56
3.70
3.90
4.11
4.37
4.87
4.56
4.30
4.10
3.73
3.58
3.41
3.15
Code

  2
  3
  4
  5
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
     If you happen to have the differentials out and can see the gears, you can count teeth and be 100% accurate of your ratio.  To do this, count the number of ring teeth, and divide that number the the number of pinion teeth.  Let's say  you count 37 ring teeth and 7 pinion teeth. 

37/7 = 5.29

     There is another method which consists of spinning a tire and counting the revolutions of itself and the number of times the driveshaft spins.  I'm not sure of the validity of this method and removed my previous instructions for it.
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