Have been tossing around the idea of going to 3:55 gears from my 4:10. I know swaps are hard as well as expensive, so I thought I might be able to just find a 3:55 complete axle and swap it out. That seems doable, but are rear ends expensive? Just wondering. This may not even be worth it, but tossing it around. What say you guys?

 

As for rear ends being expensive or not, shouldn't be bad. I paid 350 for my dually rear axle. It had all new brakes on it too. I got a pretty good deal, but I wouldn't pay over 500. One thing though, it was an older axle, so had a shorter pinion in it. This I think would have worked with a ujoint swap in the driveshaft, but would have pulled the driveshaft another 1/2 inch out of the slipjoint. I don't think that would have been major, but I decided to put my ring and pinion in this housing, and completely go through it with all new bearings and seals.

If you know how to set up a rear end, you could buy new gears and use what you have. If you don't, you could still check around on costs to regear what you have. Won't be real bad since it would be only the rear axle. One thing, you never know what you will find when you get in an axle, so be prepared. When I pulled my ring gear out of my single axle, I found a bearing going out on it. That was part of the reason I decided to rebuild the whole thing.

Why do you want to switch to 3.55's? I thought you towed that camper quite a bit.

 

3.55's? that kinda low for a truck, what are you looking for mpg's? Is it 2 wheel drive i hope, cause you have to match the front as well. I would do that gear swap instead of the whole axle, its not that bad and if you dont have the tools or knowledge a local trans shop shouldn't charge more than 300 bucks to do the install, and you will know everything is new and ready for a beating. David 7.3

 

easier to swap axles than gear sets.

 

I tow 12k with 3.55s in my truck. No problems. Makes for about 19 mpg unloaded and 13 towing 12k, for me anyway.

 

It may be a six of one, half dozen of the other. I would lean towards a gear set with new bearings and I would probably tickle the fancy of 3.73s. I'm pretty sure that's what my sled has in it now I sit at 1900-2000 rpm on the highway 65mph. Someone correct me if I'm wrong on the ratio

 

OBS came with 3.55's or 4.10's.

Super duties come with 3.73.

I run 2100 at 65 with 4.10's and tires in signature.

 

Well there you have it. The only thing is I know I'm not that hight in rpm's, but maybe the aux. idle is out some. I'm pretty sure mine sits at about 1950. Who knows though. A neighbour of mine ordered his truck new and specified 3.73's. He did tell me that it was a custom order though. I'll take a look at the tag and maybe if I ever get the motor back together I'll pay a little more attention. It's been a while since I drove it and can't remember 100% what the speed a rpm sit at. I like to keep it just under 2k but I always do 70mph. Now I'm real curious to know what's in there

 

Um, it's the stock ratio......

We're at 2050-ish RPM at 70 MPH, 3.55s and ZF5s, stock 235/85R16s.

 

Thanks guys for the input. I am just wanting better mpg. I'll prolly just look at having a shop do the swap. I don't have all the tools and no clue bout lash and all that stuff. I may not even mess with it, but I figured better mpg, new bearings and gears, so what do I have to lose? I tow a decent amount, but my experience is that the 3:55 will be just fine. My trailer is just under 10k (9800). I should be good there. Sounds like a different axle may be more $$ in the long run due to the possibility of wear and tear, etc....

 

I think I was quoted $1k front, and $1k rear to set up a set of 4:10 gears.

Have you considered going up a size or so in tires? Sometimes that can help out on the RPM aspect without the cost of a gear swap (if you need new tires at the same time).

 

Well, I just got new tires a few month a ago, so can't do that. Plus, I like the look of the stock 235s. I think it would look silly to go any bigger. I have a 2wd, so swapping gears out is not too bad. I may not even do it. I just have to figure if the fuel savings is enough to justify a $700 swap. I plan on keeping this truck for quite some time. It just broke 200k miles so it should last quite a long time with the mods I have done to it. I get about 15 mpg now, sometimes less with all the around town driving, but I was able to pull off 17.9-18.2 on my Texas trip last January. That was all highway of course. If I could get up to 18 around town and 20-21 on the highway, I'd be pretty stoked about that!

 

I don't think you'll gain that much in mileage Byron. That dually is a big truck. Honestly with that big heavy truck I'd be suprised if you gained more than 1mpg. Town driving you are going to push the throttle more to get going with the taller gear. I'd almost say you may lose a hair in town driving, and pick up a hair on the highway. Towing mileage would kind of depend on how fast you drive, but probably wouldn't change much.

I don't think it would be worth it.

 

Thanks Darin! This is the kind of input I need before doing a big job like that. I only go around 65 when I am towing. I might do 70 on flat, open interstate, but not always. Looks like I'll be doing other stuff. My mpgs aren't terrible anyways. Sounds like it wouldn't be worth it like you said.

 

You bet Byron. It's about 300 rpm difference at 65 iirc with stock height tires between 3.55's and 4.10's. The dually won't like 3.55's at 65 towing unless you run in drive. Mine didn't when it was a single rear axle with 3.55's, that was with about 10k behind and stock injectors. Any hill I'd be kicking out of OD.

I think you're wise to put the money elsewhere too.