2nd Gen Non-Engine/Transmission Changing Gears

[sparks57]

I had absolutely no clue how bad these 3. 55 gears work with the extra high OD in the auto transmission. I plan on running D25 springs and 315/75s, but that is out of the question with these gears.



I'm not in the possition to pay for new gears and all that, but if somebody close by wanted to swap, I'm all for it.



So let me ask this: how hard would it be to just swap with somebody who has a 4. 10 or 3. 73? I have the D70 in the rear.



How would I compensate for both gearing and tire changes? Can the computer just be adjusted?



Right now I run at 1850rpm at 70mph, what gearing would be best if I want to run at about 2000rpm at 70mph with 315 (~34") tires?

 

[Sixpack]

Right now I run at 1850rpm at 70mph, what gearing would be best if I want to run at about 2000rpm at 70mph with 315 (~34") tires?

That is what I run with 285's and 3. 55's. The final drive ratio of the auto and the 5600 are very close. 6th gear is 0. 73 and overdrive is 0. 69.

 

[Silver_Ram]

My 02 ETH/DEE has a Dana 80 rear axle & Dana 60 front axle. I thought all CTD did.





I run 295/75/16 BFG's & when I changed gears from 3. 54 to 4. 10, I didn't have do anything to the computer. My truck has been checked by a MAC scanner & radar, and the speedometer/computer recalibrated itself. No one has been able to explain it to me.



In about a month I will be putting 315/75/16 BFG's on, because I want to drop the rpm's (2300) @ 70 to around 1900-2000. All of the tire-gear ration calculators gave different results, than what I ended up with.



If some one wanted to swap, I don't see why you couldn't, no difference on 2002 I know of.



I would do the gear swap again in a heart beat.

 

[ndurbin]

1 tons have Dana 80 rears.

3/4 ton manuals have a hybrid Dana 70.

3/4 ton autos have a reg. Dana 70.



Nathan

 

[sparks57]

3/4 ton manuals have a hybrid axle??? Never heard of that, I thought all manuals had d80's.



I'm pretty sure I have the 70 in back.



But anyways, are 4. 10's going to put me between 1900-2000rpm at 70mph with 34" tires (315's)? Anyone with a 4. 10 auto, please chime in!

 

[ndurbin]

I believe its an Dana 80 center with 70 tubes if I remember right. Or something like that.



I dont remember the formula exactly but I think its something like every 1" your tire is over stock it drops the gear ratio . 10. Its been awhile since I heard that.



So if the formula were true. If ya had 30" tires (not sure what size stock ones are) and went to 34" with 4. 10 gears. It'd drop the ratio to 3. 70.



Nathan

 

[Mingoglia]

1 tons have a Dana 80h (h=hybrid)

3/4 tons with a manual also have the 80H

3/4 tons with auto have a Dana 70



I believe the 80h is the other way around. I believe everything is Dana 80 but the internals. I believe the reason for this was because a limited slip wasn't available for the Dana 80 so they used 70 guts... Isn't a big deal as you still at least have the static carrying capacity of the 80 which helps for the higher pin weight 1 tons are allowed... . but the GCVWR is the same regardless of 1 ton or 3/4 ton so the 70 guts are sufficent... . actually more than enough.



Mike

 

[Mingoglia]

One more thing, I think it's only the 3/4 tons with manuals that have the cummins or V10 that have the 80h... I'm pretty sure the V8's have the 70's regardless of transmission... . or maybe just the cummins has it. Don't remember off hand.

 

[sparks57]

Thanks a lot for the input, guys.



So anybody here with an auto and 4. 10's running 315's??? What RPM are you running at 70mph?



Thanks again everyone!

 

[SS]

Manual and 4.10's

All 1 ton trucks have the Dana 80 hybrid.

All 3/4 ton manual transmission trucks have the Dana 80 hybrid .

All 3/4 ton auto transmission trucks have the Dana 70.

(3/4 ton 5. 9L V8 gas engine trucks may have the Dana 60. )



The Dana 80 hybrid has a Dana 80 ring and pinion and internals with Dana 70 axle shafts and outers. The Dana 70 ring gear is 10. 5". The Dana 80 ring gear is 11. 25"



I run 4. 10's and 36" tires - it's just over 2000 RPM at 70 mph. A 315 would run a higher RPM at 70. I ordered the truck that way planning to install larger tires, but if I had it to do over I think I would opt for the 3. 55's. Of course with the manual transmission you can always downshift, but I find myself often looking for 7th gear as it is today.

 

[sparks57]

I see... unfortunately, I don't think anyone here has 3. 73's to swap.



But then, isn't the OD in the auto higher than the NV5600? Maybe the 315's will run close to 2000 then...

 

[Silver_Ram]

When I did my swap, my buddy at Six States couldn't locate a DANA 80 3. 73 ring & pinion, it would have to be aftermarket (ie: more money). Price, OEM parts & availability were the reasons I went with 4. 10's.

 

[SS]

But then, isn't the OD in the auto higher than the NV5600? Maybe the 315's will run close to 2000 then...

Yep, seems that your RPM would be about the same as mine. By my calculations a 36" is 5. 9% larger than a 34" and a 0. 69:1 overdrive is 5. 8% more than a 0. 73:1. Still, personally I would add power instead of changing gears - if I want to go 80 (on a closed course driven only by professional drivers ) I feel like I'm turning the engine faster than I care to. Just one guy's opinion and you know what that's worth...

 

[sparks57]

So do you guys think it's safe to run 315's with these gears? I was told it would be a bad idea.



What kind of an RPM drop would I see? Someone told me he had a 300rpm drop from his stock tires and 4. 10/nv5600 setup.



But if anybody looking at this post wants to swap, PM me.

 

[Silver_Ram]

I curious, why would it be a bad idea to run 315's with 4. 10 gears? Everyone I know with 4. 10's is looking for ways to drop the rpm's down a little and use power upgrades to find the sweet spot.



I don't know about other trucks, but my transmission doesn't act up as much since I changed the gears.

 

[Howard Durand]

I think CB Parker stated that he has 3. 55 gears but wants to trade for 4. 10's.



The 3. 54 gears on my 94 and the auto transmission is a bad enough combination and putting on larger tires would just compound the problem.

If money was no problem, I would get a US Gear underdrive unit. It installs between the transmission and transfer case so there would be no problem with 4X4 operation.

The drawback is that the drive lines and fuel tank would have to be modified.

 

[Mactruck]

I too have been seriously debating changing gears from my 3. 54's to either 3. 73's or 4. 10's. I have been running 315/70 r17's for a little over a year and although I enjoy my highway mileage(2000 rpm =75-80 mph) I would like my sweet spot to be a little more inside the allowable speed limit



4. 10's would help my towing but I don't tow that much. Last December I towed a little 6X10 ft trailer and wish I had a little lower gearing.

It is also the cause of my somewhat smoky starts.



I know one or two members have done a switch to 3. 73's with good results. Most of these were done on 2wd units though.



If and when I do the change I would love to add an ARB or a Detroit locker.

I do know of a few competent shops that would do the change I just don't want to be charged an arm and a leg. :{

 

[sparks57]

Thanks for the input!



So nobody has numbers on 315's at 70 with 4. 10's???



I really like how this truck is geared with these 32" tires, so I'm looking to just compensate for the 34" tires... so if I'm at 1850 at 70mph with 32" tires, I want to run that same RPM or slightly higher with 34" tires.