FAQ - what gears does my truck have???

[K5Chris]

so basically, this question comes up 3 or 4 times a week.... can we get a sticky on this or something?

option A: if you know the gears nor the glove box have not been changed since the factory, open your glove box and look at your RPO code list.

GENERAL MOTORS RPO CODES:
RPO............Ratio
GM1............2.59:1
GU2............2.73:1
HC2............2.76:1
HE3/G44.....3.07:1
GU4............3.08:1
GU5............3.23:1
GU6............3.42:1
GT4............3.73:1
GT5/GT8.....4.10:1
HC4............4.56:1

option B: pop the diff cover and look at the number stamped on the ring gear. look at the last 4 group of numbers. should look something like this: 11 41 10 76
11 = teeth on the pinion
41 = teeth on the ring gear
10 76 = manufacturered in october of 1976

take the teeth on the ring gear, and divide by the teeth on the pinion, and round to the nearest hundredth. or use this:

Ratio | Ring | Pinion
2.59 | 44 | 17
2.72 | 49 | 18
2.73 | 41 | 15
2.76 | 47 | 17
3.07 | 43 | 14
3.08 | 40 | 13
3.23 | 42 | 13
3.42 | 41 | 12
3.55 | 39 | 11
3.70 | 37 | 10
3.73 | 41 | 11
3.90 | 39 | 10
4.09 | 45 | 11
4.10 | 41 | 10
4.11 | 37 | 9
4.56 | 41 | 9
4.86 | 34 | 7
4.88 | 39 | 8
5.13 | 41 | 8
5.29 | 37 | 7
5.38 | 43 | 8
5.71 | 40 | 7
6.14 | 43 | 7
6.17 | 37 | 6
7.17 | 43 | 6

option C: pop the diff cover and count teeth. it can be hard to see the pinion teeth, and is usually just easier to read the number on the ring gear. use the method above to find ratio from teeth count.

option D: spin the pinion yoke and count the revolutions of the wheel (not very accurate, but will give you an approximate value)

[Hoss4x4]

What if we changed the chevy FAQ and change the subject title and added just post of stuff like that!

[AJMBLAZER]

Another vote to make this sticky. Useful and pertinent info.

[Chris]

Good info.

[Mr.SelfDestruct]

Been wanting to ask. But thought i would look like an A**






Thanks

[cummins4x4]

Instead u can do this http://www.currieenterprises.com/calcula...orlist.htm

[Country Boys Ram]

thanks man...

[chevy87]

Great info!

[.v.]

I'm new at this. Option D sounds closest to how national drivetrain told me to find my current ratio. 3.05 was the answer. Mark the driveshaft with chalk and with the rear wheel off the ground, turn it twice. Call them with the number of times the chalk went around and they'll tell the ratio so they know what extra parts are needed to change the ratio.

I hope their formula is right.

[jreece20]

(11-18-2004 02:00 PM)K5Chris Wrote:  so basically, this question comes up 3 or 4 times a week.... can we get a sticky on this or something?



option A: if you know the gears nor the glove box have not been changed since the factory, open your glove box and look at your RPO code list.



GENERAL MOTORS RPO CODES:

RPO............Ratio

GM1............2.59:1

GU2............2.73:1

HC2............2.76:1

HE3/G44.....3.07:1

GU4............3.08:1

GU5............3.23:1

GU6............3.42:1

GT4............3.73:1

GT5/GT8.....4.10:1

HC4............4.56:1



option B: pop the diff cover and look at the number stamped on the ring gear. look at the last 4 group of numbers. should look something like this: 11 41 10 76

11 = teeth on the pinion

41 = teeth on the ring gear

10 76 = manufacturered in october of 1976



take the teeth on the ring gear, and divide by the teeth on the pinion, and round to the nearest hundredth. or use this:



Ratio | Ring | Pinion

2.59 | 44 | 17

2.72 | 49 | 18

2.73 | 41 | 15

2.76 | 47 | 17

3.07 | 43 | 14

3.08 | 40 | 13

3.23 | 42 | 13

3.42 | 41 | 12

3.55 | 39 | 11

3.70 | 37 | 10

3.73 | 41 | 11

3.90 | 39 | 10

4.09 | 45 | 11

4.10 | 41 | 10

4.11 | 37 | 9

4.56 | 41 | 9

4.86 | 34 | 7

4.88 | 39 | 8

5.13 | 41 | 8

5.29 | 37 | 7

5.38 | 43 | 8

5.71 | 40 | 7

6.14 | 43 | 7

6.17 | 37 | 6

7.17 | 43 | 6



option C: pop the diff cover and count teeth. it can be hard to see the pinion teeth, and is usually just easier to read the number on the ring gear. use the method above to find ratio from teeth count.



option D: spin the pinion yoke and count the revolutions of the wheel (not very accurate, but will give you an approximate value)

Ok appreciate the help, that is useful information. But also on my K10 it hasthe original gearing and motor on a little decal in the door.