Help Me Choose A Gear Ratio!

[CyberSniper]

If it already has 4.10s in it I'd just run it. The 6.2L makes more torque at 1200 than a 5.3L peaks at. It will never want to go past 4th, but... ?

If you do change gears, swap out the front for something beefier and go to 5.13s. Anything else is kind of a waste of time/money.

 

[sweetk30]

Tuning can compensate for lesser gearing but why not start with a more ideal setup?

 

[toomany]

I voted 4.88's.

Have 4.88's with 35's on my current truck with a mild 5.3/4L60E. That works out to one set deeper than the donor truck had math wise. Driving around town it's great, on the highway just under 2500 is 75mph, don't really need to go much faster than that. I feel like I could use more on the highway. Passing someone usually requires a downshift. That's more of a power/motor issue than gearing though. Also feel I could use more converter. It gets up and goes just fine as it is, just would like to get into the power right away. Moving trailers or pulling things around the yard it's perfect the way it is. I haven't tried pulling anything any distance yet so no comment there.

As @Chevy305 said, being able to tune the transmission to the truck is a huge benefit. I tried driving it with the stock tune and it plain sucked. Was into 3rd gear too soon and wouldn't down shift unless you were way into the throttle. 1st gear was way short unless you had it to the floor. That was with everything correct in the tune (tire size, gear ratio, vss, etc). Once I started playing with shift points it got much better. Now, it drives like a stock truck as far as when it shifts up/down. Having the ability to change shift rpm vs. road speed vs. throttle % is huge. Can safely say I spent more time tuning shift points than I did VE/MAF/timing tuning...and I spent a good month on it tuning those pretty much every time I drove it. So don't be surprised if you need to log some hours here.

 

[RoccoK5]

I daily drive a '12 Silverado with the 6.2/6L80/3.42 and 33" tires. The 3.42s and stock tires were an okay compromise combo for both economy and power. Since upgrading to 33"s I do wish I had 3.73s or 4.10s. However to compensate I've raised the shift points and got quite a bit of power back. The stock shift points put it in 6th at 42mph which is just ridiculous. I have it set to shift to 6th at 54mph now. There's a lot to be gained with transmission tuning on these 6L80s.

As far as power goes, the torque really starts coming in at 2000 rpm so I'd shoot to be at or just above that with highway cruising. With worse aerodynamics and much more rolling resistance, I'd shoot for a little higher. Tuning can compensate for lesser gearing but why not start with a more ideal setup?

Thanks for the post! Definitely planning on spending time tuning, and am probably going to pull the trigger on 5.13s.

If it already has 4.10s in it I'd just run it. The 6.2L makes more torque at 1200 than a 5.3L peaks at. It will never want to go past 4th, but... ?

If you do change gears, swap out the front for something beefier and go to 5.13s. Anything else is kind of a waste of time/money.

Currently have 3.73s in the 10 bolt and 4.10s in the 14bff. I need to rebuild both, so re-gearing at the same time. I'd love to go D60 up front, but haven't been able to find any locally that were within my budget. Besides, I really don't plan on doing any hardcore wheeling with this truck. If plans change and I break the 10 bolt, will cross that bridge when I get there!

I voted 4.88's.

Have 4.88's with 35's on my current truck with a mild 5.3/4L60E. That works out to one set deeper than the donor truck had math wise. Driving around town it's great, on the highway just under 2500 is 75mph, don't really need to go much faster than that. I feel like I could use more on the highway. Passing someone usually requires a downshift. That's more of a power/motor issue than gearing though. Also feel I could use more converter. It gets up and goes just fine as it is, just would like to get into the power right away. Moving trailers or pulling things around the yard it's perfect the way it is. I haven't tried pulling anything any distance yet so no comment there.

As @Chevy305 said, being able to tune the transmission to the truck is a huge benefit. I tried driving it with the stock tune and it plain sucked. Was into 3rd gear too soon and wouldn't down shift unless you were way into the throttle. 1st gear was way short unless you had it to the floor. That was with everything correct in the tune (tire size, gear ratio, vss, etc). Once I started playing with shift points it got much better. Now, it drives like a stock truck as far as when it shifts up/down. Having the ability to change shift rpm vs. road speed vs. throttle % is huge. Can safely say I spent more time tuning shift points than I did VE/MAF/timing tuning...and I spent a good month on it tuning those pretty much every time I drove it. So don't be surprised if you need to log some hours here.

Thanks for your input! I absolutely plan on spending some time tuning with HP Tuners. I'm actually looking forward to that stage of my build, because that'll mean the truck is mostly back together. As for the gears, I agree that 75mph is as fast as I need to go in this rig. I'm not too concerned about a downshift (or two) when passing, but really want to avoid gear hunting when cruising.


It's seems clear (as mud?) that I likely will not be happy with 4.56 as I had originally thought -- that said, going to make up my mind today on either 4.88 or 5.13. I need to get this project moving along! Honestly will probably exchange the 4.56s I have sitting in my garage for 5.13 and be done with it. This ratio will put me at ~2400 RPM at 75mph, which is a little higher than I was hoping for, but sounds like my best bet for what I my goals are. As a bonus, this ratio will net a 56:1 crawl ratio without a doubler (although as stated before, I care less about this than the highway manners).

Thanks again for all the input, and feel free to keep the opinions coming.

 

[RoccoK5]

Thanks again, everyone! I ended up swapping out the 4.56s for 5.13s today. Working on getting the front setup now, and damn, that pinion does look tiny!

5.13 pinion on the left, 3.73 on the right:

I'll make it a point to report back on how I like the gears once I get this thing back on the road. Who knows, could be years from now at my current rate though! Feel free to follow my build and give me shit about lack of progress!

 

[chulisohombre]

Thanks again, everyone! I ended up swapping out the 4.56s for 5.13s today. Working on getting the front setup now, and damn, that pinion does look tiny!

5.13 pinion on the left, 3.73 on the right:

I'll make it a point to report back on how I like the gears once I get this thing back on the road. Who knows, could be years from now at my current rate though! Feel free to follow my build and give me shit about lack of progress!

I think you’d be happy with those gears. With the double od you need a deep gear set with bigger tires. Ten bolts look tiny already which makes that gear set look even smaller. Lol

 

[imiceman44]

Thanks again, everyone! I ended up swapping out the 4.56s for 5.13s today. Working on getting the front setup now, and damn, that pinion does look tiny!

5.13 pinion on the left, 3.73 on the right:

I'll make it a point to report back on how I like the gears once I get this thing back on the road. Who knows, could be years from now at my current rate though! Feel free to follow my build and give me shit about lack of progress!

That's the reason I don't like the 5.13
Pinion too small and not enough gears engage at the same time. But hopefully if the gearing is comfortable enough it will not put much of a load on it and it will not break

 

[diesel4me]

I never thought much about how "lower gears" have smaller pinion gears and larger ring gears...no wonder the 3:08's never seem to fail,they have more teeth in contact and more surface area..!..

 

[chulisohombre]

4.88 would even be a huge difference from 3.42 with a bit more pinion. It’ll definitely get you into a better rpm range either way. With 37s I have 4.10 and no od and it’s usable but with overdrive and big tires it’ll burn up the trans without good gearing or running it in manual to keeping it in a good rpm range. There’s definitely a lot less tooth engagement. But it’s a trade off. Hopefully you have no problems. For what you’re doing if it’s a open diff, the 5.13 shouldn’t hopefully esplode.

 

[imiceman44]

4.88 would even be a huge difference from 3.42 with a bit more pinion. It’ll definitely get you into a better rpm range either way. With 37s I have 4.10 and no od and it’s usable but with overdrive and big tires it’ll burn up the trans without good gearing or running it in manual to keeping it in a good rpm range. There’s definitely a lot less tooth engagement. But it’s a trade off. Hopefully you have no problems. For what you’re doing if it’s a open diff, the 5.13 shouldn’t hopefully esplode.

That was my vote

 

[MAXMAN]

I think you made the right choice! I have the same engine/trans combo I going to run 5.38's with 40's. I have a buddy running same combo in his 4 door jeep (5.38's and 40's) and it works perfect. He drives that thing all over the country and the combo has worked out perfectly.

 

[diesel4me]

Despite the lower ratio gears having smaller pinions,I cant say I have seen that many diffs break them or wear out bearings,a lot of P-30 step vans had 6:17 gears up here and they hauled a lot of weight daily on highways and back roads..

I suppose the lower the gearing is,the less strain there is on the pinion in ways..like how you can crank a winch by hand,and move 2,000 lbs...

 

[RoccoK5]

I think you made the right choice! I have the same engine/trans combo I going to run 5.38's with 40's. I have a buddy running same combo in his 4 door jeep (5.38's and 40's) and it works perfect. He drives that thing all over the country and the combo has worked out perfectly.

It's encouraging to hear that there are others out there with similar combos.

Tonight I finally got some time to start setting up the gears in the 10 bolt. For initial setup I used the old pinion shim and played with the carrier shims until I had backlash within spec (0.006-0.010"). Here's what that the contact pattern looks like so far:

Pinion Shim: 0.035"
Backlash: 0.006"

Drive:

Coast:

Am I right in thinking that the pinion may be too close to the ring gear and that I should decrease the pinion shim thickness slightly? Maybe open up the backlash a bit too? How does this look to you gear setup pros?

 

[chulisohombre]

I’m no pro but it looks pretty good to me. Not too far in heal or toe and pretty well centered on the gear. Mine looked similar and ran fine. You could try moving the backlash to try and get a tad more since you are at the minimum but it will wear in and just have to watch the heat as it breaks in the first few miles. If it’s too hot you are too tight on clearance. I did that in my 14 bolt. Luckily i only went a couple miles on it and checked. Went home and opened it up .002 to get it at .008 and has been running good 10 yrs.