3.73 to 3.42

[johnnieflash]

I have a TB with the 3.73 rear and would like to replace with a 3.42. Would the best way be just to by a used 3.42 rear and swap? I don't do any heavy towing and I'm looking to increase my MPG. How much difference would this change make? Thanks.

 

[Boog2006]

Come to KY and I'll swap you mine straight up. Seriously...I'd like a lower ratio.

 

[jimmyjam]

not a lot of difference. but you should be able to get a whole rear axle from a u-pull for around $150 so its not a lot of money

 

[CaptainXL]

I have a TB with the 3.73 rear and would like to replace with a 3.42. Would the best way be just to by a used 3.42 rear and swap? I don't do any heavy towing and I'm looking to increase my MPG. How much difference would this change make? Thanks.

Nil. Especially if you drive in the city at all. I tow with my 3.42 and wish I had lower gears.

 

[Mikie]

If I remember what Rodie has had to say in the past, both the front and rear differential ratios must be the same.

 

[CaptainXL]

If I remember what Rodie has had to say in the past, both the front and rear differential ratios must be the same.

Technically yes unless you disconnect the front driveshaft and never engage the disconnect .

 

[HARDTRAILZ]

If I remember what Rodie has had to say in the past, both the front and rear differential ratios must be the same.

If its 4x4. 2wd can sling any rearend under there.

 

[tblazerdude]

Gonna be in Chicago? I have one sitting in my garage I will sell you for $50

 

[navigator]

I have a TB with the 3.73 rear and would like to replace with a 3.42. Would the best way be just to by a used 3.42 rear and swap? I don't do any heavy towing and I'm looking to increase my MPG. How much difference would this change make? Thanks.

what year TB do you have?
in 05 or 06 the sensors for the rears changed.
If I recall correctly if you put an 04 rear in an 06 TB you won't have ABS or traction control.

 

[HARDTRAILZ]

06 and newer have sensors in the axle for Stabilitrak. You can use any rear end in a pre-06 and just plug the sensor holes if its an 06 or newer. An 06 or later will accept any year rearend, but if pre-06, the sensors are not there and you lose ABS and Stabilitrak. Still completely drivable, but the dash will be lit up like a Christmas tree.

 

[johnnieflash]

Thanks for all the replies. If I can't improve my mileage much, then maybe it's noteworthy trouble. Thanks for the offer BOOG2006, but it's a little far for me. Mine is a 06 model with Stabilitrak so I'll keep that in mind.

- - - Updated - - -

Thanks for all the replies. If I can't improve my mileage much, then maybe it's noteworthy trouble. Thanks for the offer BOOG2006, but it's a little far for me. Mine is a 06 model with Stabilitrak so I'll keep that in mind.

 

[Shdwdrgn]

In light of this thread, does anyone have some good info on how best to determine an 'ideal' gear ratio? There's a lot of us here who use alternate-sized tires, and it would be interesting to set up a chart based on the three standard gear ratios versus various tire sizes, and color-code it to which combinations would work best for city/towing, standard-duty, or highway use.

Also, I believe that highest gear ratio does not always equate to best mpg (if you gears are too high, your engine has to work harder to maintain speed, especially when wind or hills are involved), but I don't know if there would be a way to estimate where you would get the best mileage -- perhaps there's a standard used for an ideal rpm at a given speed that generally equates to best mileage?

 

[navigator]

I expect the best way to maximize your mpg is to make sure everything is in good working order(tstat,02sensors, etc) and modify your driving style.

My Suburban has the DIC with the instant fuel economy and it will show you quickly where you lose your mileage at.
Take off easy and coast to a stop whenever possible will help your mpg a good bit.

 

[HARDTRAILZ]

In light of this thread, does anyone have some good info on how best to determine an 'ideal' gear ratio? There's a lot of us here who use alternate-sized tires, and it would be interesting to set up a chart based on the three standard gear ratios versus various tire sizes, and color-code it to which combinations would work best for city/towing, standard-duty, or highway use.

Also, I believe that highest gear ratio does not always equate to best mpg (if you gears are too high, your engine has to work harder to maintain speed, especially when wind or hills are involved), but iI don't know if there would be a way to estimate where you would get the best mileage -- perhaps there's a standard used for an ideal rpm at a given speed that geinerally equates to best mileage?

I know there is a link on offroadtb for bigger tires.

 

[Shdwdrgn]

Based on some info I dug up from various sites... This represents the engine RPM at 65mph for different tire sizes and gear ratios.
It seems like this would indicate that anyone with tires larger than the stock size would benefit by going to 3.73 gears for economy, or 4.11 gears for general use... Anyone care to criticize the data?

[color="#399"]	3.42	3.73	4.11[/color]
[color="#399"]28[/color]	2668	[color="#0f0"]2909[/color]	[color="#f44"]3206[/color]
[color="#399"]28.5[/color]	[color="#cc0"]2621[/color]	[color="#0f0"]2858[/color]	[color="#f44"]3150[/color]
[color="#399"]29[/color]	[color="#cc0"]2576[/color]	[color="#0f0"]2809[/color]	3095
[color="#399"]29.5[/color]	[color="#cc0"]2532[/color]	2761	3043
[color="#399"]30[/color]	[color="#cc0"]2490[/color]	2715	[color="#0f0"]2992[/color]
[color="#399"]30.5[/color]	2449	2671	[color="#0f0"]2943[/color]
[color="#399"]31[/color]	2409	[color="#cc0"]2628[/color]	[color="#0f0"]2896[/color]
[color="#399"]31.5[/color]	2371	[color="#cc0"]2586[/color]	[color="#0f0"]2850[/color]
[color="#399"]32[/color]	2334	[color="#cc0"]2546[/color]	[color="#0f0"]2805[/color]
[color="#399"]32.5[/color]	2298	[color="#cc0"]2507[/color]	2762
[color="#399"]33[/color]	2263	[color="#cc0"]2469[/color]	2720
[color="#399"]33.5[/color]	2230	2432	2679
[color="#399"]34[/color]	2197	2396	[color="#cc0"]2640[/color]
[color="#399"]34.5[/color]	2165	2361	[color="#cc0"]2602[/color]
[color="#399"]35[/color]	2134	2328	[color="#cc0"]2565[/color]

Factory ratios
Fuel economy
Increased power

 

[HARDTRAILZ]

I think thats for a 1:1 final drive but we have overdrive.

 

[Shdwdrgn]

I think thats for a 1:1 final drive but we have overdrive.

Yes, you are correct. If you happen to know the ratio of the overdrive, I can make up a new chart taking that into account.

 

[Shdwdrgn]

So I noticed I made a mistake on the original chart... We have 4.10 gears available, NOT 4.11's.

I also found some info that a typical Chevy transmission has a 0.7:1 overdrive.

I put everything together into an interactive web page here. You can change the MPH to calculate at, you can select overdrive on/off, and you can also add a custom gear ratio in the 4th column. If nothing else, it makes a good visual guide to how different gears and tire sizes will affect you.