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2007 Silverado Changing Diff Gears from 3.73 to 3.42

lryfer

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lryfer Enthusiast

lryfer

Posted
Posted

Looking at buying a 2007 4x4 Silverado with 3.73 gears. Trucks has all options i want except the deeper gears. I will be driving truck on highway going places and not towing.

 

Is it feasible to change the gears to a more friendly highway gear such as 3.42 if not going to tow? Just will drive to work and other loactions and in snow.

 

 

 

Looking at the mileage for the truck. 3.42 gets 16.3-17. Just worried that the 3.73 gears will be a lot worse.

 

Input please.

 

Thanks

savillian Enthusiast

savillian

Posted
Posted

We have a 2007 Classic with the 4.8L and 3.42's and a 2006 with the 5.3L and 4.10's. Difference in MPG is maybe 2 and this is only in higher speeds like 120 KMhr (75 MPH?) Keep em down near 60 MPH and you almost dont notice it.

brainpause Enthusiast

brainpause

Posted
Posted

If you are going to the expense of changing gears and you don't tow, go ahead down to 3.23 or 3.08, especially if you have the 6 speed transmission. Changing the gearing only 10% isn't worth the cost.

 

If you have the 4 speed, the 3.73's are good, IMHO. I have 3.42, 4speed, and want 4.10 because I tow.

 

With my 4 speed, and NO significant towing, I'd drop it to 3.23 or 3.08 if it was a highway driver. However, if you spend a fair amount of time in traffic, leave it at 3.73.

lryfer Enthusiast

lryfer

Posted
  • Author
Posted

the truck i am thinknig of picking up has the 3.73 gears and 20" rims from factory. All on build sheet.

 

Will the 20s make a difference on MPG or should i go to stock 17" if i purchase?

 

Just looking at getting the best gas mileage.

pm26 Senior Enthusiast

pm26

Posted
Posted

the truck i am thinknig of picking up has the 3.73 gears and 20" rims from factory. All on build sheet.

 

Will the 20s make a difference on MPG or should i go to stock 17" if i purchase?

 

Just looking at getting the best gas mileage.

 

 

If the total height of the 20" wheel/tire is the same as that of the 17" wheel/tire, it will not make any difference. Well, minute difference from a standing stop, as 20" hweels are typically heavier and require more energy to get rolling.

 

If the 20" tire is taller than the 17" tire, then the increase in overall diameter will effectively change the gearing. For example, 10% diameter increase will effectively change your gearing from say 3.42 to 3.23.

LAGA Enthusiast

LAGA

Posted
Posted

I have a 07 VMAX 2WD that came with 3.73 gears. I changed to 4.10 and saw my mpg go up. It takes less throttle to get up to speed and once there the AFM kicks in and stays in longer. I have never had any issues with the AFM like other people. When it kicks in and out it is seamless. With the 3.73 gears I could get 20mpg on the highway if I watched my speed, hard to do with this truck. Now, if held to under 65 mph and with the cruise on I can get 22 to 24 mpg. When I don`t worry about MPG, which is most of the time, the switch in gears along with the Blackbear tune makes the truck really fun to drive.

Gurrzt Enthusiast

Gurrzt

Posted
Posted

Keep this in mind, whenever you change your differential ratio, you need to change the "shift points" of the transmission (assuming it's an Automatic).

 

I went from 3.23's to 3.73's in my 2001 Z28 (Sara) and had to have the shift points changed to compensate for the difference in RPM (in my case >500).

 

This was accomplished when I had a "dyno tune" to also adjust the 3200 stall I had installed :)

Silverado4x4 Senior Enthusiast

Silverado4x4

Posted
Posted

The money your going to spend in a gear swap will buy you alot of gas for the little bit of mpg differance. Do the math you will see how long it will take just to pay for the gears, then after you pay for the gears in the little bit of fuel savings you may get it will take a long long time to see the savings.

lryfer Enthusiast

lryfer

Posted
  • Author
Posted

the 07 i am looking at is the classic model. will the swap work if i got the truck? your local.?

Babyhauler Enthusiast

Babyhauler

Posted
Posted

Been there, tried that, would not do it again. Especially on a 4 x 4.

I changed my 02 5.3 ecsb 2wd from 3.73 to 3.23 a few months back. I had Blackbear change the computer for the change. No mods.

I keep good records of my vehicle expenses and I might have gained 1/2 mpg. Slight increase. Shortly after the gear change, I had to change the knock sensors & a few weeks later, I swapped the O2 sensors. That gained another 1/2 mpg to the 15.5 I am averaging for the past 7 weeks. This does include extra idling since it is cold. The good thing is the lowest has been 15.1, compared to the 13 & 14 mpg I got on half the fill ups in Nov & Dec. That's got to be the O2 sensors causing that. I use my truck in sales with a lot of suburban and some rural highway use with an hour trip or 2 every week. I fill up about every 5 days with Chevron 87. I usually leave traffic lights ahead of everyone and get thru traffic at a brisk pace. I can tell the town performance & mileage is not as good. I have to mash the gas more to take off in a hurry. But my tires do not spin near as often. So I guess I am saving money there. I recorded 19.4 once but that was strictly rural 55 mph trip of 112 miles. Fill up, ride, fill up at same pump again. It does down shift earlier and more often now. It is fairly flat around here. I have pulled a 1500 lb trailer around some and you can really tell it is weaker. It is quieter on the interstate at speed, so that is nicer. I think 3.42 would have been better for my mixed driving. Or a 6 speed tranny.

Improving from 15 to 16 mpg saves 2 cents per mile at $3.50 per gallon. That is $400.00 after 20,000 miles. Hopefully the sales rep that covers the western part of the state won't quit and I will not get to do some real highway mileage testing. I hope this helps someone.

 

Babyhauler

yukon25008.1 Senior Enthusiast

yukon25008.1

Posted
Posted

I have 4;10,s with a 5 spd allison and love it.. Had 4;10,s with a 4 spd 4l85e and loved it also, street/towing..

Also remember you can always knock down the gear ratio with a taller tire,

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