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axles and gears

954 Views 7 Replies 6 Participants Last post by  Ikonoid, 
B
how do i figure out what my gearing is?
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Philip
Your listing a 91. Is it intercooled?

I found your other post. You have a nonIC'd truck. If you have a auto trans it has 3:08 gears. If it is a stick shift it is a set of 3:54's.
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Begle1
How do you know it's 3:54's and not 4:11's?
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89cummins
ok quick question, i hear that my truck has 3:07's then I hear 3:08's, are the 3:08's for the later years?
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Philip
Ok Begle I was in a hurry and forgot the 4:11 optioned axles. Blowback the 4:11's were an option also. From what I have seen around these type of websites you have a 1 in 10 chance of having them.

3:08's were the rear axle ratio. The fronts are 3:07's. Most MFG's run the front axle with a slightly different gear. Don't ask me why eather. I have never found out good reason. Just think of those two ratios being interchangable.
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B
its a stick, so im lookin at 3.54's?? can someone explain to me exactly what those numbers mean
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S
What those numbers mean is that if you have a 3.54:1 axle ratio, the drive shaft turns 3.54 times for every one revolution of the wheels. If you want to know for certain what gearing you have you can take the cover off the diff and count the teeth on the big ring gear and divide that number by the tooth count on the small pinion (the one attached directly to the driveshaft). Actually you wouldn't have to count them, the tooth count of the two gears is stamped on the ring gear.

To get an approximation of the ratio you can jack up the rear of the truck, mark both rear tires and the driveshaft yoke with chalk. If you have a positraction axle you can turn just one rear wheel and the other will turn equally with it, but if you have an open rear end (non posi) you need to turn both rear wheels together. Turn them one complete revolution and count how many times the drive shaft turned in that one revolution of the tires. In your case the driveshaft should turn about 3 and a half turns if you have a 3.54 diff.

So what does it really mean to you? Just as with your standard transmission, when you are in a lower gear (lower gear means numerically higher, but mechanically lower), first gear for instance, you have much more pulling power, but you can't go very fast. So a low rear axle ratio like 4.10:1 will give you lots of pulling power but will reduce your top speed and increase your eng speed for a given vehicle speed. Generally speaking not good for fuel economy unless most of your driving is done with a significant load.
Steve g
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I
The slightly higher gear is installed in the front on 4x4s so the front tends to pull the rear ever so slightly with 4wd engaged.
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