Could you guys explain to a noob learning all this what your talking about when you mention gear ratio. Is this how big the gears are in the differential casing ? Or is it something else ? I dont have a dodge truck i have a 98 Jeep ZJ with the 5.9 engine, and it has a D30 in the front and a D44A LSD in the rear, i belive it is 3.73 for the gearing.

 

It is the ratio of the ring gear to the pinion gear in the differential. A 3.73 gear ratio means your ring gear has 3.73 times as many teeth as the pinion. So for one turn of the ring gear, your pinion turns 3.73 times. Going with a lower gear (numerically higher gear ratio like 4.10 or 4.56) means that the pinion turns more times for one turn of the ring gear. This helps increase the mechanical advantage the drivetrain has on turning the rear tires.

Here's a good link:
http://auto.howstuffworks.com/differential2.htm

 

So the more it turns the less it will bog down ? More room to move vs trying to bog something heavy am I right ? Sorta like a bycicle go to a higher gear and it makes it easier to go up a hill or to carry your fat *** ?

Wouldnt this cause the pinion to heat up more tho ? Would a higher gear ratio also make it easier on the transmission when pulling very heavy things ?

 

Yes, just like on a bike. When you change the gear to go up hills, you pedal a lot faster but your legs aren't having to push as hard and you are able to keep moving up the hill. If you change gears the other way, you pedal slower but you don't have enough strength to push the pedals going up hills. So ya, the more the pinion turns the less likely to bog down. That's why changing to a lower gear ratio (higher numerically) is important when upgrading to bigger heavier tires that can cause trucks with stock gears to feel bogged down.

I suppose it could cause the pinion to heat up more since it is turning more for each turn of the ring, but it is not so much that it makes significant difference for most general applications.

Yes a lower gear ratio (higher numerically, which is what I think you meant) does make life easier on the transmission when pulling heavy things. The downside is that lower gears can limit your top end. So when you start picking up speed, the engine will be at higher rpm for the same speed. That is why you don't want to go to low with the gears. You won't be able to get your truck up to highway speeds because the engine would be doing too high of an rpm. The key is to find the happy medium, and then depending on your driving style, you can adjust from there to a gear ratio that you can live with.

 

There's some good info on here, so here's my two cents. I just did the whole lift/wheels/tires/gears/axles/lockers/steering thing on my 98 1/2 ton with the same equipment as yours. Replacing the axle shafts, gears, and differentials goes a long way with the stock equipment on these trucks. If you're looking to go to 35s, a set of yukon axles, gears, and some good u-joints will work just fine as long as you don't get crazy on the throttle climbing big rocks. If you keep the 38s, you can keep the 9.25 as long as you go for good chromoly shafts and a strong locker/lsd, since it's damn near a 60 right now (something like 1/16th" smaller in diameter). The steering 44 would cost as much to upgrade as it would to swap a 60 from a 3/4 ton. Randy's Ring and Pinion has a good calculator for axle gearing vs engine speed to help you find the right combo. I'm running 4.11s with my 35s and am very satisfied.

 

tire size x 0.12 will give you the minimim gear ratio to use. I've run 54" tire with Dana 44's with no problems, you just need to know what to use to make them tough.

 

somewhat of a 4x4 newbie here...this thread answered about 5 different questions I had!

 

What other questions you got?