# 3.73 or 4.10 gears ?



## CAT 245ME (Sep 10, 2006)

I would like to what would be a better gear choice for my 85 Chevy K10, I plan to swap out the 6 lug axles that have 3.08 gears infavore of a set of 8 lug axles. 

The truck had a 350 engine, TH350 Tranny & NP208 T case. For tires I ran BFG's 31x10.50r15 MT's. I found the truck was fine around town but out on the highway the truck was a little sluggish. 

I plan to go from the 31's to BFG's 285/75r16E's (a full 33" tire), the drivetrain will be the same but need to know what gear ratio would be better as well as for plowing. Also the truck is pushing an 8' Fisher. Also the engine is stock.


----------



## wild bill (Feb 10, 2007)

*gears*

the 4: will really help pick it up around town and plowing with the taller tires .


----------



## Mark13 (Dec 3, 2006)

I'd go with 4.10.

My 98 chevy- 350/4l60e/np241 with 3.73s and 285s is ok, but I'd rather have 4.10s. Especially for towing.


----------



## Triple L (Nov 1, 2005)

Id take the 3.73's anyday... I got those in both my truck and have never wanted nothin more.... Id be afraid going on a long highway cruise with 4.10's... I wouldnt have anymoney left by the time i got there LOL.... I think my duramax 5 speed allison revs too high on the highway to start out with.... but i dont drive at 55 mph either............................


----------



## BigDave12768 (Nov 17, 2006)

CAT 245ME;776549 said:


> I would like to what would be a better gear choice for my 85 Chevy K10, I plan to swap out the 6 lug axles that have 3.08 gears infavore of a set of 8 lug axles.
> 
> The truck had a 350 engine, TH350 Tranny & NP208 T case. For tires I ran BFG's 31x10.50r15 MT's. I found the truck was fine around town but out on the highway the truck was a little sluggish.
> 
> I plan to go from the 31's to BFG's 285/75r16E's (a full 33" tire), the drivetrain will be the same but need to know what gear ratio would be better as well as for plowing. Also the truck is pushing an 8' Fisher. Also the engine is stock.


285's are 32.5 Not a 33


----------



## Mark13 (Dec 3, 2006)

BigDave12768;776624 said:


> 285's are 32.5 Not a 33


Depends on the maker, Most seem to be about 32.8. Which is close enough 33 for me.


----------



## CAT 245ME (Sep 10, 2006)

BigDave12768;776624 said:


> 285's are 32.5 Not a 33


Actually the BFG's AT LT285/75R16E's are 33" in diameter according to there tire chart, there is also the D version that is 32.8" in diameter.

I have a choice on a set of 8 lug axles, one set is 3.73, the other is 4.10's.

My first truck was an 86 GMC K15 that had a 305ci, TH700R4 tranny, NP208 case and 3.08 gears. Tires were 235/75r15, so this was how the truck came from the factory, It drove great around town as well as the highway but when comparing the GMC K15 to my 85 Chev K10, there was a very noticeable diffrence.


----------



## scottL (Dec 7, 2002)

3 or 4 gears... What are you planning on doing? 4:10's are going to rev your engine more and suck more gas but, will give you more get up and go from a dead stop. The 3:73 relies a little more on the hp but, has a good ability to cruse and keep weight moving. If your over torqued and plowing then you want the 3:73 to keep the wheels from spinning all the time.

I'm guessing with the tall tires and swap out your really looking for a play toy with some voom voom so, the 4:10 is probably you - it will limit top end but, then your in a truck and above 120mph is probably not your range in the first place.


----------



## aeronutt (Sep 24, 2008)

Rather than me telling you what you want, plug your numbers in HERE and figure out how fast you want your engine spinning for a particular vehicle speed. Keep in mind the percentage of time you spend doing various tasks and how much highway time your truck will get.

My F-350 with a 3-speed non-overdrive transmission is better off with 4.10s even though 60 MPH has the engine screaming. It only does highway when heavily loaded and for short distances. 70% of my time is spent below 40 MPH. The other 30% of the time I wish I had either 3.73 gears or overdrive. For me, 4.10 is the better compromise. My D-Max has insane torque and 6 speeds so there are no compromises on gearing. I get the benefit of both high and low gears.


----------



## CAT 245ME (Sep 10, 2006)

Thanks for the reply's guy's. 

I'm not building a play toy out of the truck (but it would be nice). Since I am doing a frame up rebuild of this truck I want the truck to have more ground clearance compared to stock. 

I believe now that I would be better off with the 3.73 gears for what I plan on using the truck for (mainly plowing), I have a choice between two sets of 8 lug axles to go with. The first is a 10 bolt & 14 bolt semi floater with the 3.73 gears. The other set is a Dana 60 & 14 bolt full floater with the 4.10's.

I could leave the truck stock and run the factory 28" tall tires but I dont think any body here would want to run car sized tires on a full size truck. Keep in mind the engine in this truck was rated at 160HP and 260lb-ft of torque, not very impressive numbers by today's standards.


----------



## Mark13 (Dec 3, 2006)

CAT 245ME;776834 said:


> The other set is a Dana 60 & 14 bolt full floater with the 4.10's.


I'd go with those. 1 ton full floating axles would be my choice way over a 10bolt front and a 14b sf rear.


----------



## sven_502 (Nov 1, 2008)

CAT 245ME;776549 said:


> I would like to what would be a better gear choice for my 85 Chevy K10, I plan to swap out the 6 lug axles that have 3.08 gears infavore of a set of 8 lug axles.
> 
> The truck had a 350 engine, TH350 Tranny & NP208 T case. For tires I ran BFG's 31x10.50r15 MT's. I found the truck was fine around town but out on the highway the truck was a little sluggish.
> 
> I plan to go from the 31's to BFG's 285/75r16E's (a full 33" tire), the drivetrain will be the same but need to know what gear ratio would be better as well as for plowing. Also the truck is pushing an 8' Fisher. Also the engine is stock.


Ouch. I've got 3.42s with stock 245/75/16s and I thought it had no balls, 3.08s must be just hurtin slow. Gotta love the 1600rpm highway though.


----------



## CAT 245ME (Sep 10, 2006)

sven_502;776872 said:


> Ouch. I've got 3.42s with stock 245/75/16s and I thought it had no balls, 3.08s must be just hurtin slow. Gotta love the 1600rpm highway though.


When it comes to being on the highway, the truck is a DOG. It is hard to take, around here on the 4 lane highways were the max is 120 km's the truck wont go that fast. This is why I need lower gears.


----------



## sven_502 (Nov 1, 2008)

I meant low rpm as in better mileage on the highway. the chevrolet v8s definitely do better with lower gears they need to roar before they make any power. My dad has a 5.3L sierra and its got way more power than my 5.7L 3.42. Has to be screaming though. I would love to have 4.10s. Then run some 33s or something, instead of the wimpy 245s which are probably like 28 inches.


----------



## FBN (Dec 20, 2008)

Mark13;776840 said:


> I'd go with those. 1 ton full floating axles would be my choice way over a 10bolt front and a 14b sf rear.


What he said!!! No ball joints to worry about and those semi floater rears tend to eat up axle bearing if they're used hard. Take those 1 ton rears, freshen them up and throw the under. Will easily last 100,000 miles.


----------



## Mark13 (Dec 3, 2006)

FBN;776884 said:


> What he said!!! No ball joints to worry about and those semi floater rears tend to eat up axle bearing if they're used hard. Take those 1 ton rears, freshen them up and throw the under. Will easily last 100,000 miles.


Not to mention he would never have to worry about breaking those axles even with pretty extreme abuse.


----------



## aeronutt (Sep 24, 2008)

Don't listen to those guys! Use the 10-bolt. I'll install it for you and just charge you the front Dana 60!


----------



## 2COR517 (Oct 23, 2008)

It's not a simple question to answer, but I will share my experience. I have 4.10's in both of my trucks. But because of the transmissions, they are very different animals. They both are running (or were this winter) 235/85/16. About 31-32 inches. The 97 has the 4L80 overdrive, lockup converter. The 81 has a turbo 350 - no overdrive, no lockup. 
The 97 does about 2000 RPM at 60. I don't have a tach in the 81 yet, but I'm guessing it would be pushing 2750 at 60. So the 97 is OK for long trips/highway travel, the 81 not so much. Not for plowing, it gets interesting. The 4L80 has a 2.48 first gear, the TH 350 is 3.48. That is a HUGE difference. For the plowing, the 81 will walk all over the 97. It's unbelievable how much power the 81 has. Either set would probably be OK, but there's no substitute for low gears. And considering the fact that it's 10 bolt/14 bolt SF versus Dana 60/14 boltFF, it would be a no brainer for me. Get the one ton Dana 60 and Full Floater. And  smile  every time you hit the gas.

Oh yeah, you could also upgrade to an overdrive transmission if you want to.


----------



## B&B (Nov 4, 2006)

2COR517;777206 said:


> Not for plowing, it gets interesting. The 4L80 has a 2.48 first gear, the TH 350 is 3.48. That is a HUGE difference.


The T-350's have a 2.52 first gear....not 3.48. :salute:


----------



## 2COR517 (Oct 23, 2008)

Ahh.

Humble Pie is a dish best served.......online LOL

So why does the 81 feel so much more snappy?


----------



## B&B (Nov 4, 2006)

Just meant to inform. :waving:


Many things can influence the "feel" of vehicles. Drive train mass (1/2 ton vs 3/4 ton), overall vehicle weight and the power range that an engine develops it's best power in are just a few among many. And also in the case of these two specific trucks and their differences between an '81 and a '97 you also have electronic controls manipulating the overall feel of both the engine calibration as well as the trans calibration. It can all stack up.


----------



## aeronutt (Sep 24, 2008)

Better torque curve from the engine, better torque converter in the tranny, fewer moving parts, and possibly less weight to get moving. It doesn't take much of a change in torque characteristics from the engine to make a noticeable difference in the seat-of-pants feel. I'm not sure if the '97 era had "torque management" yet, but it's a worthless concept that is intended to prevent the engine from making enough torque to damage the transmission rather than building a transmission that can handle the torque. Not one of GM's better ideas...


----------



## B&B (Nov 4, 2006)

aeronutt;777407 said:


> I'm not sure if the '97 era had "torque management" yet, but it's a worthless concept that is intended to prevent the engine from making enough torque to damage the transmission rather than building a transmission that can handle the torque. Not one of GM's better ideas...


They most certainly did although not nearly as much as newer vehicles. And it's also certainly not just a GM thing. ALL auto manufactures use some level of TM to control torque output on virtually every vehicle. Ever noticed the torque specs on a specific vehicle model creeping up over the yeas yet not a single mechanical component has been changed? Yep, torque management and powertrain control via electronic programming..


----------

