3.42 to 4.10

silveradoHO · February 17, 2007

I am thinking of swapping out my 3.42s for 4.10s on a Z71. Just curious how much difference it made in others trucks. Did the gas mileage change much, and if so how much? Was there a big difference in take off and pulling power? Just want to know all the pros and cons before pulling the trigger.

Also, how much did you pay for your swap? Always like to know if I'm gettin' rip or not.

MrLM7 · February 17, 2007

My buddy did it to his 2000 Z71 and regrets it. Threw off the speedometer reading and he still has to swap out his front gears eventually. Can't tell accurate gas mileage yet 'cuz the speedometer is off. He bought his (Richmond) gears through Summit and then paid $300 to have them professionally installed-twice. First time, the ring lost some teeth after only 4,000 miles... Ha perfect backlash and everything... perfect break-in also. Second time, with a second set of gears, the diff lost some spider gears. Now, we're looking for a rear axle out of a 2500HD to put under it. Hopefully, it will last. (Found one for $475 at junkyard). For a grand total of about $1,400, you can easily find a better and more fuel efficient way of getting power to the ground. The only real difference it made was the truck would shut off at about 87 mph, because the speedometer was off and the truck is supposed to shut down at 98. No real power difference.

silveradoHO · February 17, 2007

My buddy did it to his 2000 Z71 and regrets it. Threw off the speedometer reading and he still has to swap out his front gears eventually. Can't tell accurate gas mileage yet 'cuz the speedometer is off. He bought his (Richmond) gears through Summit and then paid $300 to have them professionally installed-twice. First time, the ring lost some teeth after only 4,000 miles... Ha perfect backlash and everything... perfect break-in also. Second time, with a second set of gears, the diff lost some spider gears. Now, we're looking for a rear axle out of a 2500HD to put under it. Hopefully, it will last. (Found one for $475 at junkyard). For a grand total of about $1,400, you can easily find a better and more fuel efficient way of getting power to the ground. The only real difference it made was the truck would shut off at about 87 mph, because the speedometer was off and the truck is supposed to shut down at 98. No real power difference.

Thanks for the input. I already knew that I would have to get front and back done, and I have a tune from wait4me, so I can send it back to them and they can fix the speedo. I thought about getting the rear end out of a 2500 but I've had a hard time finding one. I want to put a 3" lift with 33" tires on in a couple months, that why I'm thinking of regearing.

silveradoHO · February 17, 2007

Anyone that has switched to 3.73 is welcome to comment too.

xsports33 · February 18, 2007

i went from 3.42 to 4.56. I lifted my rig 6" and put 33" on, so with the 3.42 it lost so much power and pulling abiliy off the line. My tranny was also working a lot harder. However my MPG (i drive mostly highway ~85%) was around 19-21 even with the lift and tires. Pulling my 4K boat i got about 10MPG and it was incredibly slow coming off the line and i would drop down to 2nd climbing hills. I got 4.56 because i plan on getting 35"s when i run down the 33"s. The 4.56 gave me more power than i had stock coming off the line and towing. I avg ~16-17 MPG (mixed city/highway) and my city MPG went up because i didn't have to give it so much gas to get moving. Towing I avg about 13MPG and i almost never drop out of overdrive regardless of the climb unless i decide to punch it.

HOWEVER... I installed a supercharger a few weeks ago and OMG the power and torque. Coming off the line, especially with the 4.56, is insane. i lost about .5 MPG highway and city just depends on how much i can keep my foot off it, but it went down ~1mpg. With that said, i wish i would have gotten the 4.10s with the supercharger because most of my driving is highway and i can easily chirp the tires and do burnouts when want. I figure the supercharger would have made up for any power gains i would have wanted if i got the 4.10

BUT... You don't buy a truck for MPG. Also, after much research i found out that the difference between 4.10 and 4.56 is one tooth on the ring gear, the pinion is the same size. Once i get the 35"s i'll probably stop wondering if i should have gotten the 4.10s.

Getting back to your question, changing out the gears to a higher ratio definitely increased my power and pulling ability (without the supercharger). MPG went down about 3-4 overall, but IMO worth it because i tow often and climb a lot of hills. It depends on your application. If you tow a lot around town, up hills, or an extrememly heavy trailer get the higher ratio. It really depends on your application and what you're trying to accomplish. Also, it cost me $1400 to re-gear both front and rear end

silveradoHO · February 18, 2007

Sounds like you have a sweet ride, xsports. I personally don't do alot of towing, but when I do it's about 7000lbs. I have to move my dads tractor around sometimes. Also, most of my driving is city stop and go. I checked out a couple websites and found that my rpm's would only be about 300 higher with the 4.10's and 33"s at 75mph than what my current setup is, so I'm sure it would affect highway some, but shouldn't be to bad.