Thread: need to knows for my truck

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I drive a 1993 GMC sierra regular cab long box, 2wd trim package: SL. 305 CI motor 4 bolt main, 4 speed automaic OD transmission.

I need to know what the gear ratio is, and what rear end i have and whats its ratio is.

Can anybody help me out?

Well #1 GM never made a 4 bolt 305... On the glove box door the axel ratio is printed. along with tire sizes and other info. I bought a 93 GMC in 93 and still have it. They had several different ratios. if not in glove box you will have to count turns or pull cover.

ya on the door its faded away and glove box to. i was just tryimg to save pulling the cover.

i forget the exact way but as fisher says you can jack up the truck and turn the driveshaft by hand and count how many times the wheel turns or vise versa .. someone will know ...

Unless your rear end has been swapped out, it is in all likelihood a 30 spline 8.5" 10 bolt carrier with 3.42 gears.

If you can read anything on the glove box, here’s the codes for the rear end:
G80 = limited slip
GU6 = 3.42
GT4 = 3.73

4.11's were available also, along with some uncommon ratios that could be ordered. 3.42's were a very common ratio.

GM RPO Axle & Ratio Identification Codes - Sierra Gear & Axle

The old standard is to raise the drive wheel off of the ground, note/mark the orientation of of a fixed spot on the driveshaft (say a u-joint cap facing directly at you), note/mark the orientation of the bottom of the wheel. slowly rotate the tire one revolution while counting the revolutions of the driveshaft. This should get you close. If the driveshaft rotates say just over 4 complete revolutions to one revolution of the wheel then a close guess is a 4.11 to 1 rear gear ratio.

If yu need it more accurate than that you will need to pull the cover and start counting.

Sometimes there is a tag on one of the bolts on the cover that will tell you but you cant trust that. Someone could have changed the ratio and left the old tag on it.

Originally Posted by Bug

The old standard is to raise the drive wheel off of the ground, note/mark the orientation of of a fixed spot on the driveshaft (say a u-joint cap facing directly at you), note/mark the orientation of the bottom of the wheel. slowly rotate the tire one revolution while counting the revolutions of the driveshaft. This should get you close. If the driveshaft rotates say just over 4 complete revolutions to one revolution of the wheel then a close guess is a 4.11 to 1 rear gear ratio. If you need it more accurate than that you will need to pull the cover and start counting. Sometimes there is a tag on one of the bolts on the cover that will tell you but you cant trust that. Someone could have changed the ratio and left the old tag on it.

Using Bug's approach, you can also spin the wheel multiple revolutions, keeping track of the driveshaft rotation, to increase the accuracy of the estimate. Maybe you rotate the wheel ten times, and count the driveshaft at just past 41 turns. You have a 4.11 gear. Or ten times yields just over 34, you have a 3.42. Pretty easy to find the numbers, actually.

of course then you must consider if you have a posi---did both wheels turn or just one?????????????