Gear swap from 3.42’s to 3.73’s worth it?

[4Eyedturd]

Just brainstorming, if I find a rear end with 3.73’s and Abs sensors if I would see any gain in fuel mileage around town? Current Yukon XL does fine and I’m not disappointed in the 14mpg but if I could get 2+mpg I’d do the swap. It’s not a hotrod and I don’t intend to make it either. I’d say I do 85% of in town driving which is why I’d think it would help just not sure how substantial it would.

 

[Marky Dissod]

if I find a rear end with 3.73 and ABS sensors, would I see any gain in fuel mileage around town?

Cannot quantify the answer in MpGs for you for sure, but GOTTDAMNT, YES, it's a forgone conclusion.
Look carefully at the first gears of the 6L80, 8L90, & 10L80, until you understand why.

Current Yukon XL does fine and I’m not disappointed in 14MpG, but if I could get +2MpG, I’d do the swap.
It’s not a hotrod and I don’t intend to make it either. I’d say I do 85% of in town driving which is why I’d think it would help, just not sure how substantial it would.

Again, cannot quantify the answer for you, but since you said you've an XL, I'd say you ought to even consider 4.10.
My Tahoe already has 3.73, and I'm seeking 4.10 axles as we speak - and I do MUCH more highway driving than you do.
The other benefit I cannot quantify for you is that the 4L60 will last longer between rebuilds.
How much longer depends on how much easier you are on the throttle once you realize that it takes off with less effort,
and that it will spend much more time in 3rd and 4th, and much less time in 2nd.

You won't regret it - you'll wish you did it sooner.

 

[15burban]

If gas is $3 a gallon and you're getting 14mpg that equals 21 cents for every mile. Now if you were getting 16 that drops it down to 18 cents per gallon. Is the savings of 3 cents per gallon worth it? And that's if you gain 2 mpg. If the rear-end is cheap and you have the free time. Go for it and see. If it's 4 wheel drive and you have to get a matching front it's really going to take a long time to recoup the money and time.

I'd jump up even more in gears if it were me but then again I wouldn't be doing it for miles per gallon. It would be for smiles per gallon.

 

[Marky Dissod]

If gas is $3 a gallon and you're getting 14mpg that equals 21 cents for every mile. Now if you were getting 16 that drops it down to 18 cents per gallon.
Is the savings of 3 cents per gallon worth it? And that's if you gain 2 mpg. If the rear-end is cheap and you have the free time. Go for it and see.
If it's 4 wheel drive and you have to get a matching front it's really going to take a long time to recoup the money and time.

I'd jump up even more in gears if it were me but then again I wouldn't be doing it for miles per gallon. It would be for smiles per gallon.

I stipulate to everything above, to which I'll add:
Everyone chooses to forget that, if you're the type who does not gain in smiles per gallon, you WILL gain in transmission longevity between rebuilds.

 

[4Eyedturd]

Follow up question, any particular GMT800’s come with the abs sensors in the rear? And is there a cheap way to change the ratio in the computer?

 

[swathdiver]

Follow up question, any particular GMT800’s come with the abs sensors in the rear? And is there a cheap way to change the ratio in the computer?

You're looking for JL4 which was pretty standard after 2004 but not certain.

The 2005 Yukon XLs came with either 3.42 or 4.10 gears from the factory. The short RWD Tahoe/Yukon models could have come with a 3.73 gear.

Try to stay with an axle from the GMT800 as the 900s are an inch wider if memory serves.

FuelEconomy.gov gives the RWD 2005 Yukon XL and extra mpg on the highway and the rest of the numbers between it and the 4x4 and AWD are the same with no mention of gearing.

These 3 charts show what kind of ratios and speeds you'd be looking at with the three gear sets:

3.42s

3.73s

4.10s

As for improved city mileage? Guys have reported in the positive for years, especially with pickups and the lighter Tahoe/Yukon models. I switched over to 3.73s from 3.42s last year in my Yukon XL with a 6-speed and can say the city mileage has improved and even the highway when readings are taken for a few miles at those speeds. The efficiency after a whole tank of gas seems to be a wash, no downside in mpgs and more horsepower and quicker ETs at the drag strip and around town.

If yours were mine, I'd follow GMs lead and go 4.10s.

 

[Joseph Garcia]

I'm currently in the process from going from 3.42 to 4.10 gears to improve my 'smileage'.

 

[DoubleDingo]

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[rj100]

Cannot quantify the answer in MpGs for you for sure, but GOTTDAMNT, YES, it's a forgone conclusion.
Look carefully at the first gears of the 6L80, 8L90, & 10L80, until you understand why.Again, cannot quantify the answer for you, but since you said you've an XL, I'd say you ought to even consider 4.10.
My Tahoe already has 3.73, and I'm seeking 4.10 axles as we speak - and I do MUCH more highway driving than you do.
The other benefit I cannot quantify for you is that the 4L60 will last longer between rebuilds.
How much longer depends on how much easier you are on the throttle once you realize that it takes off with less effort,
and that it will spend much more time in 3rd and 4th, and much less time in 2nd.

You won't regret it - you'll wish you did it sooner.

A lot of positive results with 4:10 gears.

 

[4Eyedturd]

I found a new 3.73 rear end for $150. Not sure if I should hold out for a 4.10 or grab the 3.73

 

[Marky Dissod]

I found a new 3.73 rear end for $150. Not sure if I should hold out for 4.10 or grab 3.73?

Were I you, I'd hold out for 4.10.

 

[gregsmy]

I have a 2wd 2010 Suburban 5.3/6L80 and it’s got some soccer mom gears like 3.08. It’s lousy to even pull a little utility trailer. Been thinking about finding a axle with 3.73 gears, but would 4.10 be better?

 

[Marky Dissod]

I have a 2wd ... Suburban 5.3L / 6L80, ... 3.08. It’s lousy to even pull a little utility trailer.
Been thinking about finding ... 3.73 ... would 4.10 be better?

FYI, thread starter's GMT832 has a 4L60E, for which 3.73 is ok-ish (for y'all; I find 3.73 barely tolerable), 4.10 would be pretty good for the vast majority of cases.

For your GMT931 with a 6L80E ... how much weight / drag do you tow/haul? Does your bubba wear big-heavy wheels and/or tires?
If you've a 2WD with 6L80E, 3.73 is enough (unless most of your towing is heavy AND uphill).

 

[gregsmy]

FYI, thread starter's GMT832 has a 4L60E, for which 3.73 is ok-ish (for y'all; I find 3.73 barely tolerable), 4.10 would be pretty good for the vast majority of cases.

For your GMT931 with a 6L80E ... how much weight / drag do you tow/haul? Does your bubba wear big-heavy wheels and/or tires?
If you've a 2WD with 6L80E, 3.73 is enough (unless most of your towing is heavy AND uphill).

It’s all stock with stock 17” wheels. I do just general towing (boat, utility trailer 3000#?). The 3.08 just feels lousy when accelerating no load, in tow mode it’s somewhat better. I am getting a Black Bear tune for the transmission to improve the shifting and hopefully improve its life span.

 

[Marky Dissod]

It’s all stock with stock 17” wheels. I do just general towing (boat, utility trailer 3000#?).
3.08 just feels lousy when accelerating no load, in tow mode it’s somewhat better.
I am getting a Black Bear tune for the transmission to improve the shifting and hopefully improve its life span.

3.08 feels lousy because the RpMs are too low, even when unladen.
Instead of aiming to keep RpM as low as possible (Normal mode) to improve MpG,
Tow/Haul mode protects the powertrain, keeping the engine closer to its torque peak by avoiding unnecessary and early shifts.

Tow/Haul mode can't do what 3.42 or 3.73 will, though - 3.42 or 3.73 will improve the tow rating,
improve city MpG, improve MpG when towing, and will extend the life of the 6L80E too.

 

[gregsmy]

3.08 feels lousy because the RpMs are too low, even when unladen.
Instead of aiming to keep RpM as low as possible (Normal mode) to improve MpG,
Tow/Haul mode protects the powertrain, keeping the engine closer to its torque peak by avoiding unnecessary and early shifts.

Tow/Haul mode can't do what 3.42 or 3.73 will, though - 3.42 or 3.73 will improve the tow rating,
improve city MpG, improve MpG when towing, and will extend the life of the 6L80E too.

That’s kinda what I thought. I think I will look for a rear axle assembly with 3.73 gears.

 

[4Eyedturd]

How common are 4.10’s and any specific flavor of GMT800 come with them?

 

[West 1]

I owned a Tahoe, 5.3L with 4.10 gears and liked it a lot, the only time I did not like those gears was on a long highway trip we did every year. 780 miles one way, across Nevada and north to Salmon Idaho area. In Nevada it is flat and straight, I wanted to go 85 but the 4.10's wanted me to stay closer to 80. Beyond that mpg really dropped. We also had a Denali with the 6.0L and 3.42 gears, it was great on that trip, 85-90 across Nevada was easy. I hated the 3.42 gears below 70 mph in that truck with 4L60 tranny.

Next Yukon had 5.3L with 4L60 and 3.73 gears, a nice mix, good on highway, much better than 3.42 around town. Now I have a 08 Denali with the 6.2L and 6L80 tranny with 3.42. Even on the highway I would like it to have maybe a 3.73 gear set.

In the mountains and towing the 4.11 were perfect so it depends on what you are looking for. 3.73 is a good compromise. Maybe test drive rigs that have the gears you are considering before spending money?

 

[Marky Dissod]

How common are 4.10, and any specific flavor of GMT800 come with them?

More likely in burbans / XLs (but not ESVs), and longer Sielverrados.

 

[DoubleDingo]

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