Gearing Help and Opinions

[Callan]

OK here is the deal.

I am considering swapping the gears in my 1993 4x4 cummins. Originally it came with a A518 and i have swapped the whole truck over to the NV4500. Love the conversion but i find that when i'm running around 60 mph i would like a few more RPM when pulling trailers and it seems to really dog the motor down when i'm around 55 MPH so often i just keep running in 4th. I even seem to get better mileage in 4th than i do in 5th.

Anyway the truck has 33" tires and 3:55 gears currently. Tire size will not be changing so i am considering changing the gears out for 3:73's or 4:10's. I have had experience with these trucks way in the past and found that the 3:73's work really well as an all around gear. But considering that i have larger tires than stock really makes me wonder if i need to go to the 4:10's to get the truck to a similar spot that i remember with the 3:73's.

Regardless i am not enjoying these 3:55's at the moment. Work great at 70-75mph but i am rarely cruising with the truck at that speed.

The truck is a fun work truck. 75% of the time there is a trailer on it.

Any thoughts or opinions?

Appreciate any feedback that you guys can give

[Remps]

I dont know if there is 373's available for 1st gen diffs, might have to go with 410's. Either that or put some pizza cutters on it. I was going to say put a Gear Vendors on it, but 4th over probably wont be much different than 5th gear anyway.

[CumminsPower59]

I dont know if there is 373's available for 1st gen diffs...

As long as you aren't going from 3.07's and using the same diffs, 3.73's can be had for the standard D60F and D70.

[Remps]

Cool, I didn't know that. 3:73's should be just right then, unless you are going to be towing really heavy. 4:10's wont be any fun when you aren't pulling anything, unless you plan on going with 35" rubber.

[RCCUMMINS89]

3.73s are what the common rail trucks have. When I had that, I felt that was the best gearing with a manual trans, I also had 35s.

4.10s are ok if you plan on not wanting to drive voer 65.... after that it's like pissing in the wind.

[bmoeller]

Had 35" rubber on my 92, and 3.54 gears with a Gutbag. I really didn't need to use 5th for towing, and still did good in the lower gears (even starting out). Sometimes it was a bit fast in R, but if it was a problem, I just used low range. No more hopping.

[Mark Nixon]

You won't re-gear a 60/70 with AAM gears.
3.73s for a Dana 70 are likely aftermarket only, but Ford used them in the Dana 60s in the 1980s.

I've an AAM from a 2007 2500 with 3.73s and disc brakes, which I have contemplated putting in my 1996, along with an NV5600, but it's like anything else, the place and the money to do it.

Mark.

[oldestof11]

I loved my 33's and 4.10's. Both truck that had 4.10's consistently got better mileage than the 1 auto I had with 3.55's.

The auto got me 14mpg unloaded.

[RCCUMMINS89]

Mark, I would love to have that rear axle and tranny..... the problem is I don't wanna pay for it.

[Mark Nixon]

Mark, I would love to have that rear axle and tranny..... the problem is I don't wanna pay for it.

I didn't want to pay for either of them, myself, though the rear axle is sorta' "free", anyway.
Bought an '07 6.7 truck that was crispy crittered and I saved the rear of it for a box trailer, but a 60,000 mile AAM should really be put to practical use.

I wouldn't even be THINKING of running this 2nd gen 2 wheel drive, except that, as usual, I can't sell a complete 2WD truck to save myself.

Mark.

[Callan]

After doing some math i think given my tire size 4.10's look like the way to go.

at 75 mph puts me at 2362 RPM

at 55 mph puts me at 1732 RPM

With my current setup i am getting

at 75 mph puts me at 1500

at 55 mph puts me at 2045

So this basically gives me a 200 RPM bump. Should put me where i want to be. 1500 RPM at 55 MPH is just too low.

http://www.grimmjeeper.com/gears.html

Awesome calculator, gives you all the info you need!

[dunes450r]

i think 3.55's are a great gear. they still allow you cruising gears, and pull well too. the cummins isn't meant to pull lots of rpms cruising either. 1500rpm at 55 is just about right IMO. someone posted a fuel consumption vs RPM graph and the lowest fuel consumption was between 1200 rpm and 1600rpm depending on the HP of your setup.

2400RPM is too high for me when cruising. i might get that high when pulling a long grade with a load.

[oldestof11]

I posted the graph and the 200+hp version had peak efficiency at 1700 rpms. The 160 hp graph showed peak around 1550.

[Callan]

do you have that graph? It would be interesting to see.

And to add a little bit of a twist to it all, i just picked up a P7100 motor that i'll be doing some mods to. I'll have to see how that setup works with the 3.55's and then see where i want to be. If 1700 rpms is going to be where its most efficient i'll want that at around 60mph i am thinking

[oldestof11]

180hp


200hp/500tq


Thread:
viewtopic.php?f=25&t=14132