[white cummins]

I just purchased a 99 24v 2wd auto w/ 4.10 gears. I know I will have to change the rear end gears, but what eles will I have to due. Will I have to replace the ECM, speedo gear in the rear of the trans? I would like to change the rear gears to 3.55. I thank this would help with fuel economy. All the help is great. If you need more info., please just ask.

 

[nickg]

you'd have to have the ECM re calibrated at the dealer...or mount a GPS on the dash and use that to watch your speed

 

[99BigRed]

Is there something wrong with the gears now? It would take a long time to recoup the money spent redoing everything for the mileage difference. If your going to do alot of highway driving it would be good to keep the rpms down and boost your top speed thou. I would recommend getting a limited slip rearend put in if it doesn't have already if your gunna swap gears.

 

[white cummins]

Thank you for all the advise from 99BigRed and Nickg. Now I have a direction to go in. Yes I do alot of freeway driving.

 

[99BigRed]

I've had both sets of gears. Maybe less than 1/2 mpg difference between the two. Top speed was the bonus with the 3.55's. I can go over 100. Ok I did it once cause that guy with the 2wd dodge was tailgating me and I thought I'd ride his rear for a spell and see how he liked it. I think he figured out that I was marginly unhappy with him.
Hill pulling was the 4.10's bonus. I still do 62 towing heavy up the hills with the 3.55's thou. IF I had to build a new truck I'd pick the 3.55's. If my truck had 4.10 I wouldn't change them. Just my 2 cents.

 

[TheWelder]

Imma have to pay attention to this thread cuz at some point imma swap from my 3.55's to 4.10s. Is there a substantial difference between the 2 acceleration wise? Not tryin to jack the thread but just curious.

 

[99BigRed]

Imma have to pay attention to this thread cuz at some point imma swap from my 3.55's to 4.10s. Is there a substantial difference between the 2 acceleration wise? Not tryin to jack the thread but just curious.

Towing I think it did a little. Empty it was slower believe it or not. I think prolly a auto would be faster with the lower gears maybe. The motor is so torqy that it'll pull the 3.55's easy empty.

 

[dodgediesel59]

Actually to swap gears you do not need to have anything recalibrated on these trucks. I was told how it was calculated before, but i have forgot. I know its fact because i have swapped gears on my truck. I would not swap 4.10s for 3.55s mileage gains is very very small unless you drive 80 all the time. Driving conservative with 4.10s and a stock motor i pulled high 18s low 19s. With my comp and 125HP injectors and 4.10s i can pull high 19s to low 20s. But to accomplish that i had to set the cruise at about 63. I will say that mileage pulling is way better with 4.10s. I pulled my gooseneck to Spooner which is about 260 miles from home. Total weight behind me was 14,200 lbs. Half way up there it gets hilly for 30 miles or so. I was affraid to fill the truck. But i got 13.5 miles a gallon. With 3.55s a trip like that would have got me about 11-12 depending on how i drove. It all depends on application i suppose.

 

[dodgediesel59]

It just came to me. The reason gears dont affect speedo. The sensor reads an exciter ring on the carrier for the abs. The sensor is reading how fast the wheels are turning, not how fast the driveshaft is turning. Therefore gears dont affect speed reading.

 

[SmokinRed]

I would go with 3.55 on a 2wd...the only reason why i wish i had 4.10s is cause i'm sitting on 37" tires

 

[Phily]

It just came to me. The reason gears dont affect speedo. The sensor reads an exciter ring on the carrier for the abs. The sensor is reading how fast the wheels are turning, not how fast the driveshaft is turning. Therefore gears dont affect speed reading.

Correct. Here is a good picture. It's a D-60 and not a D-80, but you get the point:

http://upload.wikimedia.org/wikipedia/commons/9/9b/Dana_60_Dodge_4.10_gears.jpg

 

[JZOMBEK]

Yes, like mentioned before theres a sensor on the top of the axle housing that reads that gear mounted on the differential, so no calibration needed.

Also, I just recently swapped my 4.10s for 3.55s, because I feel 4.10s are unecessary in a truck equipped with a Cummins; especially with a manual, but since you have an auto it may be different. 4.10s are usually sought after by someone with an underpowered vehicle looking to gain some torque, or someone who hauls often, or is into off roading. Since I don't fall into any of those categories 3.55s are perfect for me. 4.10s in a manual also makes 1st, and 2nd gear virtually useless. The swap can be done for pretty cheap as well. I got a ring/pinion set, and a installation kit with all new bearings, seals, and shims for under $400.

Thats just my .02, though...hope I helped you out some.

 

[Pork]

Imma have to pay attention to this thread cuz at some point imma swap from my 3.55's to 4.10s. Is there a substantial difference between the 2 acceleration wise? Not tryin to jack the thread but just curious.

yes, substantial difference acceleration wise. i had 3.55's in the truck in my sig. recently wrecked it. ended up buying another 02, same as mine but with 4.10s... i installed most of the stuff off my old truck to include my drag comp. i will say that this new truck runs like a raped ape! it is really fast.

only negative is that doing 75 on the highway i'm at about 2300 rpm, and it tops out about 109-110 at 3200 rpm with stock 265 tires


on my old truck, i could hit 115, and it still probably had some left in it.

the way i see it, as far as racing goes, i'm not fast enough to see 110 at the end of the 1/4 so for now its a good thing. at some point i'm gonna put 35s on it too and i'll want the extra grunt for those

 

[dodgediesel59]

If you do buy new gears, please do not cheap out and buy the cheap chinese gears as you will pay for it. The cheap gears do not hold up to the amount of power a cummins can put out. Get dana gears. I have 3.55's for a dana 60 front and dana 70U sitting in my shop with less than 20K miles on them, would sell if you want/need them.

 

[1975mack]

it all depends on tire size. if you stick with the 265 size 3.55 r the way to go for fuel economy. 4.56 is very powerful but you wont go very fast. 4.10 is in the middle good towwing, relitivly high speed, good power. personally i have 3.55 and they do just fine for towwing, and it goes pretty fast to. you can look up the ratio per tire size. The main thing that matters in the ratio is aplication and what size tires you want.

 

[Offroadjunkie]

unless your doing the work yourself, as far as the regear. it will be cheaper to just buy a used rear end with 3.55 gears and bolt it up yourself. Only hard part about swapping an axle like that is you have to bleed the brakes. all the rest is just nuts and bolts. You could probably do it in a couple hours. Otherwise your looking at say $150-300 for gears $130-150 for a rebuild kit plus labor for the install of the gears.

 

[Pork]

^^^ as far as that goes i got a rear axle you can buy! Dana 70 with 3.55's, limited slip, and rear disc brakes!
102,000 miles on it. PM me is ur interested

 

[HI HO Silver Away]

i wish i had 4.10's! i have the 3.55's with stock 265/75/16 tire, and an auto. during spring and fall i'm consisntaly grossed out at 25,000+. sometimes even hitting 30,000. pulling our chemical trailer and anhydrous tanks. when i had the 95 12v with 4.10's it wouldn't lose any speed on hills, my 01 with the 3.55's does, have to make sure i'm on the power going down the hill, and then back off about half way up. but i pull fast too...65-70 on county roads, 75 on interstate. both trucks were 4x4, but the 95 got 21mpg empty, 13.5 loaded. 01 is 11-12 loaded, and 18 empty.
i also shift it manually, and kick the od in at 60-65 mph. imo it saves on the trans. never had to replace it yet, still stock, with 180,000+ on it.
just my two pennies!!

 

[macaw]

If You are going to keep stock or close to stock size tires the switch to 3.55s is worth it. If You are going to put tall tires on it (kind of useless with 2wd) keep the 4.10s. I was just running 265/70-17s when I switched to 3.55s but with the 19.5s (33" tall) I wish I had the 4.10s back.