Re-gearing a '98 Dakota

[280Z Turbo]

My dad's 1998 3.9L 4x2 Dakota (5 speed) is torquey, but it doesn't seem to be living up to its potential due to tall gearing. To make matters worse, it has taller 235/75/15s in place of the puny 215/75/15s.

Would it be possible to regear the rearend for some more power and low-end torque? We wouldn't want to spend a lot of money.

It really doesn't make sense to have a 3.21 differential on such a torquey engine that doesn't even rev to 5k. I think that shorter gearing would not only help acceleration, but it might even improve gas mileage, because of the way my dad drives (likes to lug it).

[sparkplug]

The difference in tire sizes is about an inch.
235/75/15
Conversion to inches
235/25.4 = 9.25  Width of tire
9.25*.75 = 6.93  Aspect ratio or rim to top of tire.
(6.93*2)+15 = 28.8 Height of tire

It would probably be a good idea to have something like a 3.40 to 3.55 range. Taller tires does help your gas mileage. It would be less expensive to go back to a smaller tire.

[Catman]

The difference in tire sizes is about an inch.
235/75/15
Conversion to inches
235/25.4 = 9.25  Width of tire
9.25*.75 = 6.93  Aspect ratio or rim to top of tire.
(6.93*2)+15 = 28.8 Height of tire

It would probably be a good idea to have something like a 3.40 to 3.55 range. Taller tires does help your gas mileage. It would be less expensive to go back to a smaller tire.

Welcome aboard sparkplug! :D  

[280Z Turbo]

The difference in tire sizes is about an inch.
235/75/15
Conversion to inches
235/25.4 = 9.25  Width of tire
9.25*.75 = 6.93  Aspect ratio or rim to top of tire.
(6.93*2)+15 = 28.8 Height of tire

It would probably be a good idea to have something like a 3.40 to 3.55 range. Taller tires does help your gas mileage. It would be less expensive to go back to a smaller tire.

Taller gearing does NOT always help gas mileage.

For example, if you started out in top gear on your bike all the time you'd have to work harder than if you started out in a lower gear. Additionally, it wouldn't be good for your chain if you were always standing on the pedals and forcing them down.

The motor turns under 2.5k at 75 mph. That seems too low, IMO, seeing as how we don't use the Dakota very much on the freeway.

I was just wanting to know how trucks are "regeared". I hear about guys doing this all the time, but I don't know what would be involved.

BTW, we just got brand new tires! We don't want to replace them with a tire that doesn't fill up the wheel well as well.

[Run Away]

It would probably be just as expensive to change the ring & pinion gear in the rear axle then to buy new tires (depending on the cost of the tires).

IMO, live with it or get your father to allow the engine to rev more between shifts.
You won't be saving ~$400 in gas by changing the gear ratio.

[Run Away]

Do you know what kind of rear axle it has?    
* Dana 35
* Chrysler 9.25 in
* Chrysler 8.25 in

Mark might know.

[93JC]

As far as I know V6 Dakotas had Chrysler 8.25" rear axles.

(The Dana 35 was used as the front axle in 4x4 models, never in the rear. The 9.25" was exclusive to 5.9 R/Ts, again, as far as I know.)

[Run Away]

http://store.summitracing.com/default.asp?...8962+4294902626

http://store.summitracing.com/default.asp?...2355+4294902626

Purchase price of those two items, then the labour (an hour and a half should cover it I think). Depends who does the work.

[sparkplug]

I think regearing would definitely help overall acceleration. I mean you would probably want to put different gears in despite the size of the tires. I mean if you were to drive your mother-in-law around you would definitely need stronger gears.  :D
I also believe the lower gears would allow you to go uphill and downhill without shifting as often and without lugging.

As a friendly guesture let me figure out how much they charge.

$50 hour.

1 hour scatching his posterior
2 hours getting the vehicle on the lift.
3 hours getting the vehicle off of him.
2? hours of actual working on the vehicle.

The bill comes to $10,000 plus 2? for pain an suffering.

I know that was a bigger help. Now you can ask a real mechanic for a real price. I'm just a big joker. Ok, a big, fat, ugly joker.

[280Z Turbo]

Sounds like it would be cheaper to pull the whole rear axle out of a wreck. That would still cost too much, I'm sure.

I didn't think that a ring and pinion would cost so much. I guess I'm just spoiled...I changed my differential for free.

Thanks anyway guys.