Rear gear decisions..

[RandyS8229]

Hey guys, I've got an 85 c10 350/th350. I am in the process of a 90s 4" spindle lift. I've decided to go with 33s. My truck came with 2.73 in the rear. I just finished rebuilding my th350 and it's time to regear. I'm torn between 3.73 and 4.10 or 4.11 or whatever it is for 12 bolt. Anybody run a similar set up and want to share opinions? I only drive 50+ very rarely and for short amounts of time. Like 30 40 min on the interstate to orlando

[RandyS8229]

If anybody wants to know it's a mild and tired 350. K1102 cam. Performer carb and intake. Poll like 8.2 compression. Headers 2.5 in exhaust. And probably poorly tuned.

[KQQL IT]

3:73 and 32's where decent In my 77, never tried 33's. Went back to low riders.

[N2TRUX]

Originally Posted by RandyS8229

Hey guys, I've got an 85 c10 350/th350. I am in the process of a 90s 4" spindle lift. I've decided to go with 33s. My truck came with 2.73 in the rear. I just finished rebuilding my th350 and it's time to regear. I'm torn between 3.73 and 4.10 or 4.11 or whatever it is for 12 bolt. Anybody run a similar set up and want to share opinions? I only drive 50+ very rarely and for short amounts of time. Like 30 40 min on the interstate to orlando

Has the rear end been changed? Your 85 didnt come with a 12 bolt, it should be a 10 bolt. Regardless of what axle you have, you cant go from a 2.73 to a 4.10 gear unless you change carriers too. I believe your 2.73 is running a 3 series carrier which will only accommodate up to a 3.73 gear. To go any lower you will need a 4 series carrier.

With that said, I think 4.10s would be a better choice if your running 33's and a TH350.

[RandyS8229]

Originally Posted by N2TRUX

Has the rear end been changed? Your 85 didnt come with a 12 bolt, it should be a 10 bolt. Regardless of what axle you have, you cant go from a 2.73 to a 4.10 gear unless you change carriers too. I believe your 2.73 is running a 3 series carrier which will only accommodate up to a 3.73 gear. To go any lower you will need a 4 series carrier.

With that said, I think 4.10s would be a better choice if your running 33's and a TH350.

I am aware or carrier breaks and whatnot thanks. I have a 12 bolt from a early 70s truck in my garage I'm going to rebuild then swap rears. It has 2.76 gears in it now. The carrier break is 3.42 iirc. But I have found "thick" gears that will fit the 3 series carrier. Do you have any advice on using those?

[tucsonjwt]

Of course, gas mileage will be affected by rear end ratio. When you are up in the high 3s or 4s your mpg will suffer. My choice has always been for the low 3s, even into the 2s, but I don't care about performance. If you want performance then you need the 4s, but highway driving will be limited. My squares have all ben 3/4 tons, so mpg is lousy with any rear end.

[RandyS8229]

Yeah I'm not worried bout gas mileage. I want that feel it in your balls when I punch it. But I also don't want it to be useless abovery 40mph lol. I've been driving around in 2nd gear the past couple days and it seems like it's running high rpms but I'm used to the 2.73 so I'm trying to get used to it. 2nd is 1.52 * 2.73 = 4.14 so it would be like 3rd with 4.11s. But I don't get the satisfaction of good launches so it's weird. Lol

[RandyS8229]

With 28 (stock) tires and 2.73 is stock. So 20% bigger tires is 33. 20% lower gear to compensate is 3.27. But I want a lower than stock feel. Some came 3.08 stock. 3.08 and 20% is 3.69. With that 3.73 would be stockish feel as well. So I'm thinking 4.10. I wish I could find some 3.90 for 12 bolt. Happy medium. SO MANY NUMBERS!! lol

[rich weyand]

If you are changing out gears, I would go with 3.73 and 31" tires. To go 33" tires, you would really want a 4.10, and that means a new carrier as well, as has been pointed out. The BFG All Terrain TA KO2 just became available in 31x10.5R15, so you can go to the best tire out there if you are an all-terrain tire guy.

Now, if you find a 4.10 axle for decent bucks (good luck with that), then do the axle swap and go with 33s.

[wilkin250r]

I've run several similar combinations. If you were like me, and routinely running 70mph freeway speeds, the 3.73 would certainly be better. I think you could easily run 3.73, but since you said you're rarely ever running over 50mph, the 4.10 sounds a bit better, but not by much.

My personal opinion would be, even though the 4.10 sounds better for your usage, I'd probably still opt for the 3.73 if it made a price difference with a new carrier.

[Mattchu60]

I went to richmond gears site - these RPM's are at 60 mph:

- with 4.10 gears it would be 2500 RPM
- with 3.73 gears it would be 2280 RPM

Personally I would go with 3.73 gears.

[RandyS8229]

Would there be a noticeable difference in feel between the 2?

[hatzie]

I put a spreadsheet up on the service manual thread that takes all the fun out of it...
If you input your transmission ratios, axle ratios, and tire size it'll generate a table of RPMs to road speed.
RPM_Gear_Axle_Transmission_TransferCase.zip
This is a screen grab with the .ODS file open in Libre Office.
Libre Office will open XLS files too but there are formatting issues.

[bmchevy1979]

I currently am running 33s with 3.73 gears in my k5 and it does great on the highway but it lacks a little down low my motor has a little bigger cam than yours but with the gearing I can hit the freeway and do 70mph without issues. With the lighter chassis of a 2wd and your cam it should do just fine 4.11 you will be wishing you had overdrive at higher speeds. I'll end up going to them in my rig but I don't drive it on the freeway everyday anymore and it's a trail rig so I need more gearing down low

[RandyS8229]

Lol lacks a little down low with muncie. I have never hadone a 4x4 but 6 something 1st and 3.73 is 24 somethin 1st gear ratio. Mine is 6.88 total for first. Hence getting rid of 2.73s. I've been riding around in 2nd and I think 4.10 is a Lil low. I don't like the feel of 45. But the 2nd gear band might be throwing the feel off. It's a breaking band for manual 2nd right? So it would make it not coast so well