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3.07 gears???
- Thread starter aceroth
- Start date
Swap the 3.07's for 4.10's in the OP's truck. Unquestionable as to which accelerates better and has a better crawl ratio.
Go get on the freeway. Do you like the RPM's at 60? No? Throw a .7 OD in there and now what? 2500RPM down to ~1750RPM? Hardly inconsequential. Better crawl, better freeway RPM's.
No, you don't need OD to get there. But for the vast majority that don't prefer manual trans, it's OD to get decent gearing and performance while keeping RPM's where people like on the freeway.
I'll posit that trying to get 33's and 3.07's moving, with the 465 and a small block, under many conditions, is going to suck. 3.42's are doable in (edit) second gear on flat ground, 3.07's would probably be near horrid. I can't imagine how much additional (painful) shifting I'd have to do between the un-synchro'd first and second, that I'm able to avoid due to slightly "better" gears. Considering the 465's first gear for any sort of normal everyday shift scenario is disingenuous IMO. Sure, you can do it. But it's no fun compared to the synchro'd second. Valid for crawl ratio of course, but even ignoring first, the gear spread is horrid. 3.58 to 1.7 is a massive drop, and no converter to somewhat mitigate it. Something like a 60% drop between those two gears, vs 40% for the TH350, and I assume the 700 is similar.
Go get on the freeway. Do you like the RPM's at 60? No? Throw a .7 OD in there and now what? 2500RPM down to ~1750RPM? Hardly inconsequential. Better crawl, better freeway RPM's.
No, you don't need OD to get there. But for the vast majority that don't prefer manual trans, it's OD to get decent gearing and performance while keeping RPM's where people like on the freeway.
I'll posit that trying to get 33's and 3.07's moving, with the 465 and a small block, under many conditions, is going to suck. 3.42's are doable in (edit) second gear on flat ground, 3.07's would probably be near horrid. I can't imagine how much additional (painful) shifting I'd have to do between the un-synchro'd first and second, that I'm able to avoid due to slightly "better" gears. Considering the 465's first gear for any sort of normal everyday shift scenario is disingenuous IMO. Sure, you can do it. But it's no fun compared to the synchro'd second. Valid for crawl ratio of course, but even ignoring first, the gear spread is horrid. 3.58 to 1.7 is a massive drop, and no converter to somewhat mitigate it. Something like a 60% drop between those two gears, vs 40% for the TH350, and I assume the 700 is similar.
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I can vouch for the idea that 3.07's with 33's would bring the suck for acceleration. My 75 with a 350/465 and 3.73 with 35's absolutely sucked on acceleration. Pulling hills? Yeah that sucked too. It's more dynamic than just looking at the straight math of gear ratios. Like it was said earlier, larger tires are heavier and you always loose mechanical advantage when going larger on the tires and staying the same on the gearing. Like my 75 I could cruise at 65 almost 1000 RPM's less than I could with the same gearing but with 31's. But with the 35's it took a hell of a lot more to get up to speed than the 31's did.
There is no free lunch as they say.
There is no free lunch as they say.
As already stated in some of the replies the new transmissions have the low gearing which means you don't need the low axle gears. Even with "only " 3.23 axle gears a truck with a 8L90 has the same 1st gear take off ratio as an older TH400 truck with 5.89 gears. Plus with the extra gears of the newer transmissions you can keep the engine in the right powerband without the big RPM drops between shifts.
For some of the other comments made by people about why the manufacturer didn't do it some other way.....trust me, I'm sure they had teams of engineers doing the calculations and testing prototypes of different transmission vs. axle gear combinations to determine which works best. There are many factors to consider such as which combination offers better fuel economy, better performance, cost benefits, manufacturing capability, design parameters......basically what may look best on paper may be very expensive to make or just will not fit. For example, may be very hard to design and cost a lot of money to make a 1.5:1 axle gear set for a rear axle, and again not practical to make a 7.5:1 gear set for an automatic transmission.
I have LS3 with 4L60E on 33's. Went from 3.73 to 4.56 and my fuel economy went way up. Probably doubled. All of my driving is local. Up and downhills and around curves no trips longer than 20-25 miles. Why did my mileage double? Accelerator never needs to move more than 3/4" and I am ripped off the line like a rocket with no effort on the engine or the tranny and I'm cruising 2000 @ 60. Even at cruising speed I may be turning 2000 but with almost no skinny pedal. More than RPMs skinny pedal effort is fuel economy. Who wants to drive a K5 with no anti-locking brakes and no airbags 80 MPH for a 100 miles down the interstate anyway. I drive my truck almost every day and love the way it accelerates and love the fuel economy.
To your first point, I'm not concerned about high final drives for low speed crawl / take offs. I'm well aware that transmission gearing can overcome that for the short moments it takes to get up to speed, hell even my 160hp 305 feels like it can pull a house down in low / low gear with 3.08 axles. What I do care about is how well it can maintain 75 with a load behind it (as in not making 4 gear changes on every hill), and the final drive ratio plays a significant role there. That ratio is literally the size of the lever you have on the axle, and once you are in a 1:1 or higher gear, it doesn't care how many gears you have, extra leverage always helps.
And to your second point I agree as well. I'm sure part of it is they had to make one transmission to fit a variety of applications such as 5.3 and V6 trucks, vans, etc. However, when you tell me that I can get a 3.73 with a 5.3 but not a 6.2, i tend to believe the only reason they make decisions like that is to cover their own ass on warranty claims. Similar to not offering a 6.2 in a regular cab.
Similar to not offering the 6.2 in anything but the high trim levels?
That too. Let me buy a muscle truck dangit!
So someone already hit on this a bit but to make it clear
You want 4.10 or 4.56 gears on the new trucks but they offer 3.23.
Compare the new trans 4.56 first gear to the 700r4 3
05 first gear.
So swap axle gears with first gears you have the same take off ratio in first.
Now you get to overdrive, not only you have more with the 0.61 but it's paired with 3.23 gears so rpms are low and it fine with the new engines because their torque curve is more flat and starts pretty decent just off idle.
Now you mention the multiple downshifts going uphill that is the result of more speeds.
When you have a powerglide with only 2 speeds, you will hardly ever see it shift.
8 gears it will shift 4 times as much to stay in the powerband
More speeds is only part of the problem. Having less leverage on the axle is the other component because it applies to my sm465 K10 with 3.08 gears just the same. At 65 on the highway 3.08 isn't enough of a torque multiplier and it cant maintain speed up a hill to save its life. In comparison my overdrive / 3.73 trucks seem much less bothered by hills.
I'd agree that a modern 6.2 has enough torque to overcome it, but considering that most people opt for the 6.2 for towing purposes, limiting the gear selection seems ludicrous.
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urbex
1/2 ton status
Are the OD/3.73 trucks set up identical to the 465/3.08 truck other than the trans/axle gear? I'll bet not...and I'll also bet that the 465 truck is an older carb'd model, whereas the OD/3.73 trucks are newer EFI trucks, which plays a much bigger part in this than many realize, even if they're producing similar power numbers.
They are, and I fully admit those things are playing a role in that too. But I still believe anything less than a 3.42 sucks in a full size no matter what the config. One of my good friends leased a 14ish K2XX silverado with a 5.3 and a 3.08 and he made the comment that he should have paid more attention to the window sticker when he got it and that he couldn't wait to get rid of it because of how much of a dog it was. It had the big chrome wheels on it which probably made the problem even worse. About a year ago he traded it in for another one with a 3.42 and he's much happier. Same engine/trans.
Boy, you really started a debate!
When I first bought my '79, I "assumed" that it had what my '77 has, 3.73. NOPE, my '79 has 2.76. 4WD Low isn't slow enough when the road or trail get rough. I have a brochure for the '79 and 2.76 is listed. Out of curiosity, I looked for '73 K5s and found the below page, 3.07 is listed as factory. Be glad you don't have 2.76!
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Same set up on my '79 K5 when I bought it. I feel your pain! Still have the 2.76 and SM 465. Couple yrs ago bought a set of Cooper 235/85R16 and rims from Discount Tire. That made a noticeable difference, but still isn't very good on the trail at low speed.My 81 Jimmy came stock with 2.76:1 gears and a SM 465. You needed to use low to get it moving before shifting to first and so on. If you didn't the clutch would chatter something horrible. It cruised great on the highway though...as well as terrible gears it had 33's on it too.
Plan to put either the 3.73 from my '77 or 3/4 ton (4.10) set up from a '76 pickup. Issue of time and $....
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I lost those 2.76 gears in a hurry, went with 3.73's and some 35" General grabbers...then 36" TSL's..then eventually to tons with 4.56's and 39.5 TSL's. It's a progression, kinda like a bad coke habit. (and almost as spendy) 
Read and heard the same, which is why the "older" 4X4's isn't recommended to run in 4WD on dry pavement.
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I lost those 2.76 gears in a hurry, went with 3.73's and some 35" General grabbers...then 36" TSL's..then eventually to tons with 4.56's and 39.5 TSL's. It's a progression, kinda like a bad coke habit. (and almost as spendy)
Worse. I could probably break a coke habit!
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My theory is that the Fed may have required a minimum fuel economy or the manufacturer just wanted to falsify it for the window sticker so they put a real tall gear in one, got it on a flat stretch of highway with a tailwind and done their testing.
In reality the trucks would’ve gotten much better fuel economy with 4.56 gears because most driving is local.
My truck lugged itself to death trying to drive 60 in OD with 3.73s.
I used to think the same and I drive a semi, most used to be 3.55-4.10
Now they run 2.23
And they pull 80k lbs and can easily go 80mph on highway and pull up the hills 40mph.
My 3.55 geared 2012 runs 30mph up the hills and struggles with 80mph on flat.
Newer engines have more power but also have it at lower rpms.
Mine dies below 1200rpm the newer engines are still pulling at 1000rpm.
We can go on with this debate but the point is that absolute numbers are not necessary, combos define a successful truck
