Rear end gears and transfer case speedo gear

[sethv]

Hey guys. I need to find the correct speedometer gear for my truck. But first I'll need to figure out my differential gear ratios.

Using this calculator, http://www.apexgarage.com/tech/gear_ratios.shtml, and doing roughly 2100 RPM, I was doing 55 (passed a sign that tells you your speed), so I put this info in:

30.5" tires
4th gear's ratio of 1
And I assumed my rear end was 3.54, but it would also be close if I chose 3.42. (for the final drive)

So which was more common? I know it's gotta be one of those two, but I cannot pull my diff cover (I can't afford the extra fluids as of right now).

Also, which color was the speedometer gear for the rear ends? The junkyard told me they were color coded and to let them know which one I needed.

Thanks guys and sorry if I'm missing anything.

[79BIG10]

Look here for a great article on getting the rear axle gears found out. http://73-87.com/7387garage/drivetrain/speedo.htm

[gchemist]

Use this calculator.
Find the best whole number combo for gears.

http://www.tciauto.com/tc/speedo-info