Which axle 3.08 or 3.42?

[dmarty]

Hey Guys. I’m spec’n out a new 2012, 5.3 LTZ 4WD to replace my ’99 and want to know what axle ratio to get. Dealer says 3.08 is standard, but I’m think’n that’s gona be too doggy, but maybe I’m wrong. He says most people get a 3.42. That’s what I thought I had in my ’99 5.3 4WD 4L60E, but I found my window sticker and it says I have a 3.73 which I really like. Tire diameters are the same ‘99 vs. ’12 (different wheel size, but overall diameters are same) and ratios of the 6L80E in the ‘12 are 4.03, 2.36, 1.53, 1.15, 0.85, 0.67 and the 4L60E in the ’99 are 3.059, 1.625, 1.00, 0.07 so it looks like the ‘12 will have a slightly higher gear ratio (lower numerically) in OD, but much lower in first than the ’99 so I’m thinking that I might go with the 3.42 as the 3.73 will be way too low in first. I’m an old guy and like a little performance, but still want decent mileage as I drive about 30k per year. The truck is lightly loaded at about 200-300 lb plus driver most of the time. I have a small utility trailer that I take to the lumber yard a few times a year, but never pull a boat or RV trailer and all of my driving is in the Midwest on freeways with no mountain roads. So what do you think is the best ratio for me 3.08 or 3.42? Thanks!

[dmarty]

I think I just answered my own question. I should have done the math before my post. If you multiply the trans ratio by the axle ratio you get the overall ratio. The '99 OA ratios are 11.41, 6.06, 3.73, 2.6 (first to fourth) and the '12 with a 3.08 are 12.41, 7.27, 4.71, 3.54, 2.62, 2.06. It looks like the '12 has a little lower first gear, a 5th gear that's equal to the '99 4th gear and an even higher 6th OD. Looks like the 3.08 might actually be pretty similar to my old 3.73 and may be the way to go. So, my new question is how do you like your 3.08 or 3.42? Also has anyone had a 4L60E with a 3.73 and switched to a 6L80E 3.08? Thanks!

[willinwtx]

my 08 rclb had a 3.73 with the 4l60 and my 11 rclb has a 3.42 with the 6l80 i find them pretty comparable. the 08 was around 2100 rpm @ 70 and the 11 is 1800 rpm @ 70. as far as driving the 11 actually feels like the 1st gear is a tad bit lower than the 08. I have had a few people tell me that there truck feels pretty sluggish with the 3.08 gear.

[dmarty]

Thanks for the info. If you look at the overall ratios, your first gear is lower in your '11. I'm still on the fence here. I've heard that a 3.08 can be a little doggy, but I'd like the better MPG. A friend says his '08 is constantly downshifting at the slightest hill. Can't trust the salesman, he says whatever I want to hear. Seems like a big jump from 4l60 3.73 to 6l80 3.08, but the OA ratios aren't that different in the midrange, just a little lower first and a lot higer sixth. Anyone else?

[piecesparts]

It depends on your tire size, but my 3.42 is a good combo with my 2011 GMC and it's 20" rims and tires. I get a good acceleration feeling and really decent mileage. I am running a 30.4" tall set of tires on my truck.

[dmarty]

Thanks for the info. The 265/65 R18's on the 2012 and the 265/75 R16's on the '99 both have a dia of 31.6". With your smaller tire dia, your overall ratio will be a little lower. I'm curious, do you use the manual button much? If I get the 3.08, and it turns out to be a little too low, I may use the manual +/_ button to drop down a gear on hills. Have you tried that?

[willinwtx]

i run a 245/75/17 which is 31.5 tall and rarely does my truck shift out of 6th with 4-500 lbs of weight in the bed. the only time i had to use the manual buttons was with 10k worth of pipe and trailer then i had to use it to make it hold a gear or it was all over the place. you have to think of what motor is in it, these ls motors really like to rev you get the 3.08 it is going to put it down around 1400-1500 rpm cruising well out of where the motor is making power thus making it work harder or search for a different gear.

[dmarty]

Thanks for the feedback. You're right, the 6l80 with a 3.42 has OA ratios of 13.78, 8.07, 5.23, 3.93, 2.91, 2.29 wich means that 4th in a 4l60/3.73 falls between 5th and 6th in a 6l80/3.42. But you have a much lower 1st which from my experience I don't need. It seems that the extra gears of a 6l80 are wasted on lower first gears. I'm leaning toward the 3.08 and hoping for better MPG, but it may be too sluggish. Gona place my order tomorrow, not sure which way to go. Thanks again!

[piecesparts]

First comment for my perspective---the 3.08 will make you hjate it by the time that you get the truck home from the dealer.

I have the 6-speed auto in my truck and I like the acceleration of the truck with the 30.4" tires. My truck came with 255/55/20 (31.9") tires and I downsized due to the fact that I lowered the truck 4" in the front and 6" in the back. I will tell you that the RPMs on the truck are just about right for my driving and I have no issues.

[dmarty]

Nice looking truck. What axle you running?

[piecesparts]

Originally Posted by dmarty

Nice looking truck. What axle you running?

I have a 3.42 rear end gear on this truck and it runs at 2000 RPM at 75 MPH. My 91 SWB daily driver had a 3.42 and it was good all around gear for getting around and also for getting traction when needed. My Son's 86 had a 3.08 gear in it and that limp piece of a arag was worthless. We upgraded it to a 3.73 and now the truck is a truck not a moving violation.

The truck in the picture averages around 19 to 20 MPG and that is running with our new highway speeds of 75 MPH and has plenty of pull on an acceleration. I would like a lower geared rear end for more bite, but it would cost in fuel economy. The 3.08 will cost in both respects, because the economy will only exist if you don't work the truck hard to make up for the wimpy rear end gear and only if you drive it as a car.

[dmarty]

Thanks for the info. I ordered the 3.08 yesterday. I may regret it. I figure I will have to use the manual mode to keep it from going into 6th at 40 MPH. I've looked for a repromgramer, but only found ones for 4 speeds. I ordered the 3.08 because it didn't make sense to have two extra gears on the low end. First in my truck is pleanty low enough now and the new one with a 3.08 will have an even lower first, so I figured the 3.08 is the way to go as the 3.42 will have a much lower first. I'll just have to use manual mode, but that may get old fast. Time will tell.

[piecesparts]

OK, if that works for you Good Luck.. It would be my guess that you will be working the truck harder than you want to get the performance that you desire and in the long run using more gas to accomplish what you will want it to do. I would think that you could change your order before it gets too late. I have seen some with gearing to high to allow for a good driving ability and they have to make up for it otherwise. Then you see the truck on a used car lot.

I have no issue with the 3.42 gears and with the taller tires on my truck, I am definitely not to low in gearing. I run a decent RPM on the highway and get a good 19 to 20 MPG on my daily driving (That is mixed highway and city) Let us know how you do when you get it. Maybe I am too power hungry and performance oriented to see the good side.

There are programmers out there, but I had a friend do a EFI Live tune on mine. That is a little more adjustable than a small box program can do. I would also look at the power enhancers that are available on the market. Cold Air kit, free flowing exhaust.

The latest Super Chevy magazine had an article on getting more HP out of a 5.3 Chevy engine. They gained over 100 HP total, in stages to show what works. The cold air kit and the headers were a great combination and added approximately 40 horses. They did one at a time and showed on a dyno the changes. These engines respond well to a little massaging.

http://www.superchevy.com/technical/...ild/index.html

[grayharville]

I have a 2010 gmc crew Z71 with 3.08s and I actually like them. My motor has plenty of balls to haul the truck around without having to compensate for power with gearing. Its cruises at 70 and will govern out in 3rd gear. Its a six speed, id like to see what it'll do with a custom tune.
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Ps. The 6 speed is a great trans, I like the gearing and overall feel of it.

[piecesparts]

I just put on a set of Long Tube headers last weekend. Along with the Magnaflow and the dual 21/2" outlets, the truck runs pretty strong for a 5.3. Went to verify the tune after the headers and it was not off very much from what we left it, last spring. I still believe the 3.42 is the better rear end gear ratio.

[grayharville]

It might be a better ratio, to each his own though. Mine does what I need it to do.
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[dmarty]

Thanks for your input garyharville. I'm going with the 3.08 and hoping to get better mpg. I think the gearing is ok, but I'm thinking a reprogram for the trans will be needed.

[grayharville]

I drive mine fairly aggressive all the time and get around 15 mpg. If I drive right its more like 17-18. I think you'll be happy with it.

Today I towed an 18 foot trailer loaded down with a 79 chevy, I didn't even turn the tow/haul on! And Not a single problem pulling 65 mph
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[dmarty]

Thanks for the info.

[Bill72BB]

dmarty;
Just wanted to find out how you like your truck with the gears you ordered .
I just was pricing a 2012 1500 LT Crew cab and was looking at the 3.42 vs the 3.08 .
Would be interested in your MPG as we would us the truck for traveling .

Thanks

[piecesparts]

Just my .02 worth, the 3.42 gears are a better all around gear ration for a truck. Especially if your tires are relatively tall. I get 19 to 20 on th ehighway with a 30.5" tall tire and running at 70 MPH+. The 3.08 gears, in my worlkd would take to much torque away from driving and truck usefulness.

[dmarty]

I've got 10K on the truck now and I'm happy with the 3.08 gears. I don't do a lot of hauling, usually just 200 to 300 lb of equipment plus a fiberglass topper and the ocassional trip to the home store or landscape supply place with a small utility trailer, about 4000 lb max. The MPG wasn't that great at first, but now that it's broken in it's better. I recently did a 250 mile RT on the interstae with the A/C off and a little bit of in town driving and got 21.1 MPG. I'm happy with that. A couple of times I was driving with a light load in a hilly area and had a head wind and the trans was hunting between 5th and 6th gears. I put it in tow mode and it stopped. I've also tried the manual mode to keep it in 5th when it hunts and that works too. Just to repeat, this has only happend a couple of times and is not a big deal for me. If I had lots of $ and didn't care about MPG or did a lot of towing, I would go with the 3.42, but for my needs the 3.08 if perfect. BTW, my average MPG from day one with 10K miles is 15.7. That includes a lot of idling in the winter here in Wisconisn for my job as I do a lot of outside work and need the engine on to keep me warm. The truck and wheels are factory original. Like I said, I'm happy.

[Bill72BB]

Thanks for the imput .I would be happy with 21 on the road also the best I ever got with my 2000 and 2006 Tundra was the High 18's .
The thing that got me curious was how the 6 speed auto would react in town
at 25-45 mph . with the 3.08's .

[dmarty]

No complaints what so ever in town. One difference I didn't mention is that the '99 4-speed in tow/haul mode had very harsh shifts, but the 2012 6-speed has smooth shifts in tow/haul mode.

[piecesparts]

I found that my 6 speed auto tinds to get into the 6th gear and then a little detonation is noted when you try to accelerate in moderate traffic. This can be solved by dropping into manual and setting the gear selector to 5th gear and that issue goes away.