Has anybody went from a 4:11 or 3:73 to a 3:42?

[HANK1948]

I am contaplating using my 83 1 ton SW 2wd crew cab for my daily driver, but I would like to more MPG out of her, Iam sure it has a 4:11 or a 3:73. I was thinking of putting a 3:42 in it but I dont know if it would be worth it how much more can I get? I have a 88 R20 2wd burban right now and it gets 19-20 with a 3:73 I drive (no faster than 65-70) 120 miles to and from work a day.

[Ratau]

Hank

What size wheels? My Blazer got 33 X 12.5 wheels with 3.08 gears. It revs around 1600 at 75mph in OD and 2000rpm at 60mph. In 3rd. To little power on even small uphill. For the 33

[slagona]

I replaced the 4:10's in my '87 1 ton Dually Crew Cab with 3:52's. It was about 8 years ago - they didn't make any "higher" gears at that time for that rear end. I think they do have 3:42's now - or so I've read on the forum.

It didn't really affect fuel mileage that much - but I did it so I could go faster - it was my daily driver and 60 miles each day on the interstate at 60 mph just didn't cut it - was able to go 70 mph after the change...... More wind resistence was probably the reason why my mileage was about the same after the switch. I also swtiched the tires to a taller tire - allowed me to go about 75 mph. I have a peninsular 320HP 6.5TD in the truck, so power wasn't a problem - pulled a smaller 5th wheel up any hill at 65mph.....

For me it was worth it for the speed increase. Putting 30K miles a year on that vehicle - saved me a lot of time.....

[HANK1948]

tire size is 235/85-16, Iam not worried about towing thats what I have my 96 for.

[cschneider]

I made the switch to 3.42s but not for mileage, but for durability. With the TH400 I felt the engine was screaming at 70mph. I have a banks turbo so power is not a problem at all. I think I got the whole thing done for about $1400 including installation, new bearings, Auburn posi and quick loc for the front. I think it was one of the better investments I made in the truck.

[jbell]

I have 4.10's as well. Pulled th400 and replaced with 700r4. Was cheaper than gears, and with the lockup converter, I get 20mpg at 70-80mph. Was getting 16 before, and 65mph was MAX I could drive.

Have the same size tires as you, and can tell you that not only will it get better mpg with the 700r4, but it accelerates faster as well. (and the noise/rpm's are much much better)

My 2c.

[moondoggie]

Good Day!

In my 95 pickup, I went from 4.10 gears w/ 8% oversize tires (effective overall ratio ~ 3.80) to adding a Gear Vendors & 4% oversize tires (effective overall ratio ~ 3.08). I keep REALLY accurate (IMHO) mpg data, but it's still pretty hard to get an accurate idea how much my mpg changed. My best GUESS is a 2 mpg improvement.

To figure out when a modification will pay for itself, put this in your spreadsheet program (do NOT input the quotes

[Ratau]

Jbell

You run 700r4 tranny with 4.10 gears and what size tires to get 20mpg? I want to go to 3.74?? or 4.10 for better uphill performance.

Danie

[jcomp]

I get 16-19 MPG with a 700-R4, 4.10s and 37" tires. That's up in the mountains or here in the valley at 7800 ft. The engine lugs down going up the passes around here. I plan on switching to 4.56 or 4.88 gears and hopefully I'll gain a MPG or two.