Hi all, I'm new to the forum and hoping to be a new Cummins owner within the next couple of weeks. I have been reading topics on this forum for about a couple of weeks trying to decidde what is going to suit us best. I think I have narrowed it down to a 3500 Quad 2wd DRW Cummins 555. The only thing I haven't decided on is whether to get auto or 6-speed.
The question I had was has anyone thought about or changed the axle ratio back to 355 or even 342 to help with get better mileage at higher highway speeds? Would a 342 and 6-speed be a good setup? I would not have the axle changed right away but maybe later down the road when I may want to up the power. I was not sure what the effects would be besides making reverse gear even taller than it already is. I live in Georgia and the towing we do would be primarily to Florida. We will be towing our boat which is about 6000# total and thinking about getting a small slide-in camper.
Thanks

 

Welcome Aboard bubblechaser. I don't think I've read here where someone took a 3rd gen AAM to 3.55 or higher. FWIW, the difference between 3.73 and 3.55 is so close, that if you did see any improvement in fuel mileage it would probably be neglible, and probably take a hundred thousand miles for the cost savings to cover the cost of the gear change.

I'd stick with the the 3.73 and use the money you saved for other toys....

 

Has anyone got an overdrive unit like from US Gear. What kind of setup? Something like a 410/6-speed? Just trying to look down the road when I get a slide-in. Usually I'm driving @75 and was looking to help improve mpg.
Thanks in advance
Steve

 

If you get an auto, and you're only towing 6000#, 3.73 will be fine. My truck with bigger than stock tires flings around my 5000# trailer like its not even there.

If you plan on towing heavy, get 4.10. My truck with oversize tires and auto and 3.73 had a hard time with 19500# GCW.

 

Or swap it over to 19.5s tires and wheels.Like Ricksons.Lower RPM and LONG tire life.When I can thats proberly the route I'm going.

 

I'm a bit confused; you are purchasing a 1 ton DRW diesel truck which is designed to pull 15,000#+ with the right axle and you will be pulling a 6,000# trailer. I think a 1500 Hemi would do the job reasonably well (a bit thirsty on gas). Most people that buy a 2500 get the diesel(80%+ DC says - the 3500 only comes with the diesel). On top of it, you want to make the rear end taller - to save fuel cost - thereby reducing the towing capacity of the truck.

I think the automatic would be fine for your application - My truck pulls a 6,000# horsetrailer on the flat easily at 120km/h (which is as fast as I want to haul horses) and gets about 12mph (us gal) at 65 mp/h.

Some people (on this forum and others) have concerns about the longevity of the auto. I'm sure there will be more problems with the auto compared to the manual - so I'd consider that. As for the axle, I'd leave it alone - the cost won't be easily recouped by the savings in fuel and any prospective purchaser wil run the other way if they know your truck has a 3.55 axle in it.

Just my opinion, of course

 

Thanks gor the input. I'm trying to look farther down the road because I may be doing more camping and less fishing (I can't believe I said that) later thus moving from a slide-in to a fifth-wheel. Currently we tow the boat with a '88 Chevy van (Also sleep in van) but it works that van hard. I'm hoping to come across a resonable slide-in while we're pulling the boat and doing the fishing thing. I'm probabaly about 2 weeks away from getting the truck and its been awful hard waiting.
Thanks again for the responses.

 

If you plan on ordering it?
The only way to get the 555 Cummins is if there is one on a lot somewere,if you order it it will be the 600 Cummins..

 

Well I finally got the truck. A lot of thanks to everyone one this site, it really helped me to decide. I had to fly from Atlanta to Pensacola to get it, they were the only ones close by with the options I wanted. My dealer wanted an extra $4000 to do a dealer trade.
Well anyway, I got an '04 3500 Quad Cab DRW 305/555, 6-Speed, 4.10, White, Dark Slate Cloth Seats. This is the first diesel I've onwed and I love it, so far. I just went over 600 miles on it so I should be about ready to start putting so weight on it to really break it in.
I'm still thinking of an U.S. Gear overdrive unit seeing how I've got such a heavy foot on the hwy.

 

Congrats
And enjoy that 305/555 HO,I love mine

 

BubbleChaser,

Congratulations on the new truck. I know how you felt waiting and waiting. I know you'll have fun with it.
If you decide to get an overdrive I would be very interested in hearing about the results. It may be hard to get an accurate comparison of before and after, but it would be fun to find out if there was a difference.
My question to you is why are you so convinced you'll get better mileage with higher gearing? It's not a gasser, it's already turning fairly slow, the overdrive unit adds another gear set that robs some power, and the engine seems to be right in the sweet spot of the cam. Do you have an idea of why this will work?
I'm just curious.
I have a '93 with the 3.45 gears and I put larger tires in it that raised the gear ratio. I did not get any better mileage, of course the bigger tires added more drag, but the truck felt overgeared and sluggish afterward too.
Thanks,

Wetspirit

 

To me it seems that it runs good @ 2000rpm so if I could get back to that rpm at 75 - 80 mph I would think I would be getting better mpg where it has better power.