Hello guys, I feel bad I haven't been around much, been busy setting up and working at my new shop. But since I've had time to get acquainted to my baby, I like her, a lot. So I want to start digging in. She's not the same as my first gen, but this will do just fine. The only issue that I'm having is the gearing. I'm squeezing about 16-17mpg never exceeding 65mph. So it just so happens that the mechanic next door to us specializes in rear ends/gears. He suggested throwing 3.54's in it. I thought it was a good idea but I've heard you would have to change the carrier out and it would be a little more involved than just doing 3.73's. But I figured I should go with one of the two options. I live out in the country and do almost nothing but highway driving. My shop is only about 10 miles down the road. I never tow over 10k, and I rarely tow much anymore anyway, if I do it's usually just transporting a light vehicle at the most. I've been searching high and low and haven't really found or received an answer from people who have done it. So my question is what do y'all think? Is there anyone that has first hand experience with either gearing? And if so what are you thoughts, likes, dislikes? Any info would be appreciated!

Ps: On a side note, would it be ok if I just did the rear end for now and drop the drive shaft from the front? I don't use the 4x4 much during summer anyway. I just don't want to spend a load of $$$ all at once if I don't have to and this is my only means of transportation, so I can't afford much down time. But I will do the front asap when the funds come in. Thanks again!

 

I'm almost positive the carriers are the same for 3.5-4.10, 4.56 I thought was the cutoff point. Would certainly cut the cost down. If you have a bunch of miles on it rebuilding the LSD wouldn't be a bad idea. And if you don't use 4wd, I don't see any problem with doing one at a time with the front shaft out to make sure it doesn't happen.

 

Truck only has 163k, but I may just do it while it's out. I'm getting pretty confused about where the split point is for the carrier. I read in one place that the front d60 will be fine either way, and that d80 is 4.10 up and 3.73 down. If that's true I might just have to buy the parts a little at a time. If anything I'll bug the gear guy next door when I see him again and ask if he knows. Maybe someone here knows for sure?

 

I would go the 3.54 route. Cheaper to find and less headache for speed sensing etc to get OEM change parts.

 

Contact a gear supplier, like ringpinion.com. They should know where the break is.
How much do you drive? You can buy a lot of fuel for the cost of gears and the labor to change them. If you drive a lot of miles, it may be worth it. If you don't, You will be driving a long time before you break even.

 

D80 is for sure different 4.10 to 3.54, not sure the exact ratio break.

D70,D60 is 4.10 to 3.54 the same for sure.

 

D80 is 3.73 and down, 4.10 and up.

Go with 3.54's if you swap. No point in going half measure when its gonna cost a good chunk of change. Might look at getting something like a Detroit TruTrac for it while you're in there, mechanical limited slip.

 

I'm with Tate, if they had a 3.07 option, I would almost change my 3.54's out.....

 

There's a 3.31....

Chris

 

Thank you all for your suggestions, I'll call a specialist for more detailed info for parts and such. I don't do a whole lot of driving, but I do go on some trips in the truck. But since all my driving is highway it bugs the heck out of me hearing that poor thing screaming every where I go. So how do y'all like the hauling performance of the 3.54's? I know cost wise I may not come out ahead, but it's a project truck and I plan to keep it for a long, long time.

 

I really like mine, I tow about 10k or so when I do tow and it goes down the road great, I have a manual also.

 

Go rob the diffs out of a 1st gen.

 

Didn't know they had 80's under First gens...........

I am NOT giving up my 80, unless I find a SRW 110.......

 

I asked a reputable cummins mechanic that a few months ago, & he told me with all the power & torque of a bombed cummins he knew guys that were tearing up rings & pinions using 3.08 gears. I'd love to have it personally for highway mpg.....

 

I tow 10K all the time with 3:54's running 285 tires and it's a great combo. It's the best of both worlds and I would easily do it again for the next truck.

The break is 3:73 on the carriers....3:73 and down/4:10 and up

Jeff