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Gear Help

745 Views 10 Replies 5 Participants Last post by  Dirt_devil
first off i have a 96 ext cab 3.9L v6 dakota. it has stock gears. i am gunna put on some 33x12.50x15 tires on there. my truck already doesnt have alot of power. when i put these tires own its gunna have no power. so i need bigger gears. What size gears should i get? 3.83 or maybe bigger? im not to sure about the gear thing. i need some help. also how much will gears cost? and where can i buy them from for my truck?

Thanks Matt
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or if its cheaper ill even buy a whole new rear. i just need more power to turn the 33's.
Some dakotas came with 3.91 gears check your local junkyard buy the whole diff. Tag on diff should say 3.9 or 3.91
I would go straight to 4.56 if you do not do a whole lot of freeway driving. You can get gears on e-bay and many other places online. You will need Chrysler 7.25 gears for the front axle... there is apparently no difference (gear-wise) between it and a 7.25 rear.
I have a set of 3.91- 8.25 gears I would sell for $100
if they fit my truck ill prolly buy them off u i just have to look at my truck. once i find out what rear i have in my truck ill let u know.

PS. if this is any clue to what rear my truck has it is pretty damn slow now with not much power.

by the way should i buy the same gears for the front of my truck and the rear?

Thanks Matt
The same ratio... Yes, same part numbers... No. I would Highly recommend 4.56's if you are concerned about acceleration... My guess is that you have 3.55's right now. Going from 3.55 to 3.91 is not a big jump, throw in the fact that you are increasing your tire size to 33" and you will probably end up with slower acceleration than you have now. Good luck!
im trying decide between 3.91 and 4.11 i have heard that most guys that put 4.11 in there truck also put posi rears in it. i wanna refrain from putting a posi rear in my truck. so would 4.11 work right in my truck without a posi. i do alot of highway driving because of hunting but i do go muddin quite a bit so i wanna have power but fuel economy so thats why im thinking the 4.11's

Thanks Matt
I have 33s and I put in a 3.9 gears. And I did notice a big diffence jumping from 3.55 to 3.9. So If you want econmy stick with the 3.9. If you dont mind a little less gas milage go with the 4.11s. the 4.11s will give you more power. Check out They have a chart for best power and best economy. And they also have a tire change calculator. Check out for good deals on ring and pinion sets. They have good quality stuff.
Keep in mind dodgef25 has a 5.9L (hell of a lot more torque) and Max4hdmatt has a 3.9L (a lot less torque). There is a balance point as far as engine size versus gear ratio when it comes to economy. If you need to hold the v6 wide open to maintain speed with 3.91 gears you will get better economy with the 4.11's (as well as put less wear on your drivetrain). The 5.9 can run along with a small throttle opening and low rev's with the 3.91's because it has a lot more torque.
Those gear tables are nice to look at, but one thing they do not account for is the additional rolling mass that the 33's have. You would want a taller gear than what the table says to maintain or improve over the current acceleration your truck has.
Also, you don't have to put a different differential in your truck just because you put different gears in.
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