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3.07 gears???

A

aceroth

1/2 ton status
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When I first got my 73 k5, me and a buddy did the "turn the driveshaft, count the wheel turns" test and figured I had 3.73s (tags on both diffs are long gone). It was getting late in the evening when we counted if you know what I mean so I had it in the back of my head to pull the diff cover and double check (hoping they're really 4.10).

Finally did that today and saw a some not-super-clear numbers that looked like "14:43" and either "CV" or "CW" on the ring gear. (Quick internet research says "CV" is 3.07 open and shows nothing for CW). I counted ring teeth and got 43. Not sure I counted the pinion right but sure looked like 14.

I am 99% sure my drivetrain (350/350/203/D44/12b) is untouched from factory but WTF? Did GM really send k5s out with 3.07s? Is that what I have?

Anyone disagree that this moves axle swaps up the priority list? I have a 388 almost built for it. Pretty dumb to spend money on a new engine and hobble it with 3.07s, no? I do want to be able to cruise at 65 without it screaming but with 33s or 35s, 4.10s should allow that, right?
 
That gear ratio is extremely common.
Run a gearing calculator like the one at grimmjeeper.com and select all your options and see where it puts your trucks rpms for different ratios. Gear it for how you want your truck to run with your motor specs.
 
I've read that many 4x4's have axle ratio's that are not "perfect matches" front to rear--a GM manual I have states a truck with 4:10's in the rear actually has 4:09 gears up front,they "round off" the ratio's --I guess a slight variation doesn't matter all that much..
 
Yep very common. I have the 3.07 / 3.08 in my K10. Good gear for cruising, but even with no overdrive the towing performance is non-existent with my fire breathing 305. Pretty sure ive had the manifolds glowing red pulling 2,000 lbs up the slightest grade. *yawn*
 
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. :haha:
 
I've had a few "too high geared" Gm's too--one was the '80 El-Camino Royal Knight edition I had with a 267 V8 and a TH350,with a 2:56 posi behind it..take offs were sluggish and you could wind it up to 60+ mph in first gear merging onto a highway,and cruise at 80 mph at fast idle..
Surprisingly it didn't bog down on hills,I guess it was light enough not to matter..that and an '82 GMC Cabalero I had with a 229 V-6 and 3:08 gears non-posi were the worst vehicles I ever had in snow or ice,all they wanted to do was go in circles,the rear wheels spun so easy..

My '81 G10 with 2:73 gears isn't much better,the 307 V8 hasn't got enough low end for a fast take off and like the Royal Knight I can wind it up to 75 mph in second gear before it'll hit 4000 rpm.
These vehicles all had stock sized tires..

High gearing isn't so bad if you have a BBC under the hood,and they seem to be a decent combo if you still have an old three speed automatic..
 
And then there's the oddballs like myself...I wish I could get 3.07 that fits in a 14BFF..then it would make for the perfect jack of all trades/master of none build that I want with my 454/SM465 combo on 35s. Low RPMs on the freeway with a not quite so dismal MPGs, make up the lack of low axle gears with the granny of the 465 trans, and a low range crawl ratio similar to that of the 700R4 with 4.10s. Would work fine on a rig that's not a hard core off roader. I likely don't NEED the 14 bolt at this level, but I'd like to have the FF axle for ease of maintenance, and enough beef back there that I can run a spool and have absolutely zero concern about ever breaking the axle 50 miles deep in to the open desert.
 
3.23's are out there for the 14FF.

OD and gearing are the only ways to get anything close to a multi-purpose setup running good both on and off road.

Anything that helps highway hurts crawl ratio, and vice versa. OD allows you to gear well, and still bring engine RPM's down on the freeway. With the 203 being roughly 2:1 in low, you could always play around with low range being the "primary" for off road use, you'd have to look at where the TH350 gear ratios fall in terms of MPH and engine RPM. If your goal is being able to use that power on-road under daily driving conditions, better gearing would pretty much be a requirement.
 
I really don't understand why GM is gearing the new trucks so high again, you'd think they would have learned this lesson. My dad's 6.2L 8-speed only has 2 overdrives of which 8th is on par with 4th in a 700/4L60e, yet the the only gearing options were 3.23 or 3.42 with max tow. Why not give it a 4.10 and a higher overdrive gear?
 
JoeliusZ28 said:
I really don't understand why GM is gearing the new trucks so high again, you'd think they would have learned this lesson. My dad's 6.2L 8-speed only has 2 overdrives of which 8th is on par with 4th in a 700/4L60e, yet the the only gearing options were 3.23 or 3.42 with max tow. Why not give it a 4.10 and a higher overdrive gear?
Click to expand...
Fuel economy. Plain and simple. Ever look to see what your Dad's truck is tach is riding at 65 MPH? Not going to come close with a 4.10 ratio.

Look at the gear ratios on an 8L90:
1st. 4.56
2nd 2.97
3rd 2.075
4th. 1.688
5th. 1.270
6th. 1.00
7th. 0.845
8th. 0.652

Deeper gears early negate the need for the deep gears in the diffs. But for fuel economy the tcm will get the trans into the higher gears sooner to burn less fuel. Which offsets the nice deep first gear in the frist place. I don't like it either, but it's the way things are going. This goofy logic forces multiple gear downshifts that will spook someone if they aren't ready for it. Like dumping from 7th to 4th or 3rd. Rpms jump from 1500 to 5500 in a snap.
 
"Emissions" are why high gearing was phased in early in many vehicles also..up until the late 50's ,4:56 gears were pretty common in cars and trucks..(and they had overdrives for the 3 speed manuals too!)..
After the early 60's you saw mostly 3:08 gears in passenger cars and light trucks,or even higher...in the 80's 2:56's and 2:73's started being used more..
 
If you increased the overdrive appropriately for the larger rear gear, you could turn the exact same RPM at 65 and have more pulling power. Then the transmission doesn't have to make up the difference by shifting all over the place. But I get that UNLOADED the higher gear works better and that's what the EPA is after. to me its an insignificant improvement in every day driving compared to the major loss in towing performance and efficiency it comes with.
 
obijuank5 said:
General motors new truck clientele doesnt pull anything worth noting.
New gm trucks are cars.
Click to expand...

Ding ding. We got a winner. For no more than the typical 1/2 ton truck buyer is going to tow, gm is right. I don't agree either but they are the ones pumping out half tons like crazy. The next step of warped logic is if they need better towing ability they need to step up to a 3/4 or 1 ton . That means they can nail down another $15 to 20 grand more for a truck with a dmax/Allison combo to tow anything. (With Max gearing of 3.73 iirc)

But what that does is get more idiots into diesel trucks that have zero clue on what it takes to own a new modern emissions laden diesel truck. Add to that moronic sales staff that rarely understands the diesel emissions stuff and how to use it but are quick to sell anybody a truck that starts at $60,000 for the commission. I end up with these people in the service department whining why it cost to much for an oil change or fuel filter and what's the def fluid we have to add and where does it go? Oh yeah they only tow a boat twice a year with it. The rest of the time it gets run for little errands around town which is really good for the emissions system to never actually clean itself out. Then wonder why they have to bring it into us to clean it on a manual Regen.

Did I just jump on my soap box? Shoot. The joys of a dealer service Dept.
 
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dyeager535 said:
3.23's are out there for the 14FF.

OD and gearing are the only ways to get anything close to a multi-purpose setup running good both on and off road.

Anything that helps highway hurts crawl ratio, and vice versa. OD allows you to gear well, and still bring engine RPM's down on the freeway. With the 203 being roughly 2:1 in low, you could always play around with low range being the "primary" for off road use, you'd have to look at where the TH350 gear ratios fall in terms of MPH and engine RPM. If your goal is being able to use that power on-road under daily driving conditions, better gearing would pretty much be a requirement.
Click to expand...

I don't see where there's any difference between a low 1st gear, a 1:1 high gear, and high diff gears compared to a higher 1st gear, OD, and low rear gears.

700R4 (.70 OD 4th gear)/NP208/4.10 axle/33" tire - 32.75 crawl ratio, 2046 RPM @ 70 MPH
SM465 (1:1 4th gear)/NP208/3.07 axle/33" tire - 52.56 crawl ratio, 2188 RPM @ 70 MPH....150 RPM higher is hardly noteworthy. Even if I went to a 205 transfer case, crawl ratio is still above that of the 700R4 at 39.47. Going to a 35" tire brings freeway RPMs down to 2063 RPM.

This of course leaves out torque multiplication factors from the auto trans torque converter, which is a dynamically changing number, and a debate all it's own. But this does show that OD and deep gears are absolutely not necessary for an all around rig.
 
To be honest I don't get it either because when i do a torque multiplication equation it favors the 3.07 ratio which definitely has not been true in the real world for me.

Lets say for simplicity were pulling with 100 pounds of torque at a steady cruise:

Your first example: 100 x .7 (OD) X 4.10 = 287 pounds of torque at the axle.
Second example: 100 x 1 x 3.07 = 307 pounds of torque at the axle.

Apparently the 150 rpm is significant...

This seems like one of those situations where I'd flunk an engineering class for siding with trial and error experience over actual data.
 
"torque multiplication from the torque converter", which only comes into play at low RPMs, and lowers as the converter approaches stall speed. It's really not in play at highway cruise RPMs. More or less torque at a steady cruise also means little, assuming there's enough torque to maintain a specific speed. If you need 200 lb-ft of torque to maintain 70MPH, you're not going to feel the least bit of difference between having 201 lb-ft and 2000 lb-ft, until it comes time to accelerate or pull a grade.

There's also more to it than just static numbers, if you really want to approach it from an engineering standpoint. Automatic transmissions typically sap more power in friction and rotational mass losses compared to a manual, and higher ratio gears take more power to turn than lower ratio gears. There's also tire size and weight that can affect it. Bigger tires take more force to turn just by being larger and heavier, and merely matching RPMs may not give the same performance as a smaller tire.

Really though, I'm not entirely sure what exactly you're inferring by real world results as far as the gearing differences go. My numbers were just to show that OD and deep gears weren't the only way to accomplish a task.
 
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