rear end gear changes

[jcarr]

Ok guys beat me up on this one.

i have a sterling 10.25 with 4.10's and i'm thinking of going to 3.55's for the fuel economy. let me know what you think.

i don't pull real heavy loads and living here in the mid-south not much mountain driving. probly 10k would be the heaviest i'd pull. the whole reason i got a F350 is for hauling hay and feed for my livestock and pulling the stock trailer. would 3.55's really hurt me more than the gained fuel mileage?

 

[DragRag]

10k is very heavy with 3.55's. You can do it, I have with my 92', but it will be a super ****. The gain would not be worth it, sounds like you really work your truck.

 

[typ4]

I put them in mine and if I tow heavy I drop a gear, I mostly commute or flat highway tow and the mileage difference was worth it to me. Oh and when loaded we gross at about 15k


If you dont have a turbo, get one. Big improvement.

 

[Shadetreemechanic]

I put them in mine and if I tow heavy I drop a gear, I mostly commute or flat highway tow and the mileage difference was worth it to me.

X2 I have 3.55s and tow quite abit. It tows fine on flat ground and I downshift for the hills.
My dad has the 4.10s in his 250 and I can tell you the gearing makes a world of difference on fuel economy and drivability. Only downside is 3.55's make first gear in my zf-5 a little tall for towing. If I am heavy and on a hill I put the transfer case in low range.

 

[DragRag]

I guess my experience is polar to yours. My two crew cabs have 4.10's in one and 3.55's in the other and the torque difference is very noticeable between the two. Both trucks seem to get about the same MPG's to. My 3.55 truck though with a true 10k lb load, so I am running at about 18k lbs, is a mega **** on a grade, oten bouncing down into 1st tached out at 3300 rpm pumping out black smoke! Man I need a turbo on that truck.

 

[BioFarmer93]

No thread hijack here, but a related question- How difficult is this to do? I have 4:10's & a ZF-5 and am very seriously looking into this. I'm not the Master Wrench like a lot you guys but I do follow directions well and am not afraid to get dirty. Is this swap something I can do in the driveway, or are there complex subtleties not in evidence here that can sabotage my effort? Are the new gears readily available/expensive?

 

[sle2115]

I have both and have pulled clost to a 10k load with each...all I can say is I hated the 3.55's! I don't do much highway driving, but do know that on the 65 MPH highways, the fuel guage moves about as fast as the speedo with the 4.10's! I know I pulled a grade with a load of wood (not a huge load) on the truck and small trailer that you have to start out slow on and I honestly didn't think I'd make it with the 3.55's...I can pull the same grade with the same load in 2nd with 4.10's, in fact, my truck is much heavier now too as I added the steel flatbed and DRW's since the 3.55's.

If your doing a lot of highway driving and not much towing, the 3.55's would probably be fine. I do more towing than highway, so the 4.10's worked good. I now have 3.73's and so far love them. I haven't pulled with them, but first gear doesn't feel all that much different than with the 4.10's and I turn around 400 RPM less at 65 to 70 than I did before. ZF5 going in when the weather gets better as well as a turbo whenever I can get it fixed up!

 

[Brimmstone]

I moved from Ohio to Texas in my 87 with 3.55s and a 4 speed. total rig grossed a little over 27k. I was told by a Tenn trooper to get out of his state because I was so heavy. Ran the whole way down doing 65 minimum except for one really long hill in Kentucky. Mileage sucked at 9mpg the whole trip but for the weight I could live with it.

 

[Full Monte]

I have two trucks with 4.10 in one and 3.55 in the other. Having overdrives in both, I think that would be step 1 before doing a rear end conversion. I like the 3.55s for freeway driving with the overdrive. The 4.10s on the freeway are a little too low without the overdrive on. GVW on the camper truck (see sig) is 11,660lbs. Going up grades, the 4.10s is even too tall. On a long grade, I get down to 25mph.