Anyone in here have a avalanche 2500 and swap from 4.10 to 3.73 or vise versa? Did you notice much loss or gain in fuel economy? I'm buying an 05 with 4.10s. Wish it had 3.73s I wont tow much or ever. Considering swapping gears out.

Thanks

 

It's a bigblock and 4L80-E I'd assume, so you've got low end torque but a narrow gear ratio range. If you're using this truck for highway commuting with OEM sized tires it's worth your while to replace the 4.10:1 gears since the overdrive ratio is only 0.75:1.

Figure a 30.6" tire and 65 mph:

with 4:10:1 gears - 2200 RPM
with 3.73:1 gears - 1970 RPM
with 3:42:1 gears - 1830 RPM

If you don't need it to launch strong off the line consider 3.42:1 gears. The 1-2 shiftpoint would only move up by about 8 mph.

You can expect a 1 mpg increase in highway fuel economy doing that.
If you really want to get crazy there's always the Gear Vendors Overdrive. 22% more overdrive in any gear and reduce your 65 mpg cruising RPM from 2200 to 1700 even with the 4.10:1 gears

 

Yeah, Since I first posted this a few days ago, I've found some info of guys that had the 3.73's and went to 4.10 gears and lost 0.3 mpg. on the highway, and picked up 2mpg towing. For that kind of loss i'm not even worried. Hell I drive the truck about 3k a year so who cares anyway lol. I figure jumping up to a 32.5 tall tire will almost put me into the 3.73 ratio anyway.

 

Went from 3.73s to 4.10s in my truck...would never look back. That was with a 33" tire. Picked up a solid mpg around town and with those tires had no loss on the highway. Have 35" tires now might go 4.56....The move to 4.10s the truck felt soo much better around town. The real problem is the gearing of the 4l80...I wish they would figure out the electronics for a 6l90. If it were me I'd leave the 4.10s

 

i have an 06 2500hd and ill absolutely swap gears if youd like. i have the 3.73 axles

 

PM'd You ls2 Dude,

Just an update, I drove truck home from San Antonio To My home town in MN. 1280 miles, Truck had updated 265/70/17's on it, vs the 245 75 16's. Speedometer has not been calibrated so when the truck says its going 64mph it is going 71 according to my gps. I figured its about 10 % off. And according to all the speeds I went it is about that much. I had it between 71-72mph entire trip at around 2250-2300rpm.

1st tank was about 13.1mpg, Sat in san antonios disaster of a traffic jam on 35 for a few hours. Second tank was 14.3 and last tank was 13.7. Should have been better, temp dropped about 20 degrees between last tanks, And My clutch fan is completely stuck on through all rpm ranges. sounds like a jet in front of the truck. So that probably didn't help mileage at all. Truck is real torque down low. I know it has a big block, My dad has an 8.1 and I don't think it feels that snappy off the line. But with that fan clutch locked up its very slow. belt squeels if it gets up past 3k. I'm ordering a gatorback belt. belt that's on it is for the 145 amp alt. which is a tick longer, it does feel like it has some slack. I ordered the shorter one. My alt is only a 105 according to rpo number.

Plan on changing diff fluids and trans fluid.

Didn't know the 05 8.1 had shiny aluminum intake. My dads 01 has black plastic I believe.