From 3:42 to 4:10 worth it?

[xavierny25]

Got a good deal on a used set of diffs from a 06 tbss and I wondering if it's worth switching it out? Also what else Id have to do to make it work on my Voy? I know a retune is a definte.

 

[HARDTRAILZ]

Retune wont help unless yours is 06 or newer.

I would put 4.10s in every one of these from factory to lifted.

You only need an adapter ujoint on the rear of the rear driveshaft and possibly if lifed the driveshaft shortened. I saw stock it worked without shortening, but all us lifted guys had to have an inch or 1.5 inches slicedout.

 

[xavierny25]

@HARDTRAILZ My Voy is an 08. So a tune should help right?

I planning to drop it 2" from where it sits now. So all I'll need is that adapter u-joint? Do you have apart # for that.
This might bite me in the az to ask but will this change anything as far as me being 4wd?(since the tbss is awd)

 

[HARDTRAILZ]

You can dial in the speedo and such then, so i would retune. I think it was the right thing when I swapped gearing.

The 4wd or awd makes no difference. as far as diffs go.

With the drop it should be fine with just adapter. It is 446 or 447. I dont remember right off

 

[xavierny25]

@HARDTRAILZ thank you sir for that info. Guess what I'll be picking up tonight.

 

[djthumper]

Guess what I'll be picking up tonight.

My new 4.10 differentials?

 

[xavierny25]

My new 4.10 differentials?

Turns out it will be more like Friday or Saturday at the latest.

 

[xavierny25]

Question for you guys...
Can I switch out the rear diff and run?
I plan to do the rear 1 weekend and the front diff the following weekend.
The front is a little more involved hence why I want to take a whole day in it just in case I run into any issues.

 

[Mooseman]

Probably but you have to be damn sure you don't turn that switch or pull the encoder motor fuse. I had done the same thing on my '93 S Blazer with the manual T-Case.

Unless you're adding bigger tires, your MPG are going to tank.

 

[Reprise]

Unless you're adding bigger tires, your MPG are going to tank.

Just curious, as I thought I'd take a hit no matter what...is the new size readily available? Guessing there might be two, depending if you're going to 4.10 from 3.73 or from 3.42 (etc., etc.)

There's another one available in my local area (sadly, he doesn't have the front diff, so I'd have to sacrifice the 4WD)

 

[xavierny25]

Unless you're adding bigger tires, your MPG are going to tank.

I'm getting great mileage right now. OCD maintenance will do that I guess. Lol.
What are you thinking I'd be looking mpg wise running a stock wheel setup?

 

[djthumper]

You will be fine as long as you don't engage the front differential. You may find that you get better gas mileage with the new gears.

 

[carshinebob]

My blue Bravada has a 4.10 and I get slightly better fuel mileage in town compared to my silver Bravada with a 3.73. Although I do drive very gently and the blue one is 2wd compared to awd on the silver one. I like driving the 4.10 much more. It just feels like it can accelerate with no effort where as the 3.73 needs a little more push on the gas pedal to get it moving. I've found the highway mileage to be about the same. ~BOB

 

[littleblazer]

The 02 does around 23 highway and 16 city while mine does 14 and 22. I drive it like I stole it.the rpm difference is going to be around 800 at any given speed. I don't think you'll take too much of a hit on mpgs.

 

[Mooseman]

Imagine my 4.2 with the 3.42. Bloody slow acceleration. I was thinking of swapping in 3.73 as they feel pretty damn good on the Saab with the 5.3. I could see better MPG city but hwy will take a bit of a hit because of the higher RPM.

 

[littleblazer]

It's funny, we lined up the voy and TB and the voy takes it off the line every time somehow.

 

[djthumper]

If I put 4.10 in my TB I will actually get MPG back due the larger tires.

 

[Blckshdw]

If I put 4.10 in my TB I will actually get MPG back due the larger tires.

I'm gonna chalk it up to the long day I've had today, but can someone break this down for me real quick? How does this work?

 

[Sparky]

Partly because of offsetting the larger tires with the lower gear ratio. Makes it easier for the engine to get those tires moving. Can help with in-town driving when you're doing a lot more stop and go. Lets you get to the higher gears faster with less effort and actually keeps the average RPM lower. Then, depending on your tire size and gears, your cruising mpg may even be better because you're not downshifting so easily.

My old 98 Camaro gained something like 2 mpg highway going from the stock 3.08 ratio to 3.42, and that was even before a tune for the change and just doing the math to compensate for the difference. And it was better to drive around town too. Not sure why GM didn't just stick 3.42 in all of them, but whatever.

 

[littleblazer]

Partly because of offsetting the larger tires with the lower gear ratio. Makes it easier for the engine to get those tires moving. Can help with in-town driving when you're doing a lot more stop and go. Lets you get to the higher gears faster with less effort and actually keeps the average RPM lower. Then, depending on your tire size and gears, your cruising mpg may even be better because you're not downshifting so easily.

My old 98 Camaro gained something like 2 mpg highway going from the stock 3.08 ratio to 3.42, and that was even before a tune for the change and just doing the math to compensate for the difference. And it was better to drive around town too. Not sure why GM didn't just stick 3.42 in all of them, but whatever.

On the c4s you either got a 2.56 or 3.08 with the 700r4 or manual. In later years the performance axle went to 3.31. For how you had to drive and shift for the old EPA tests it needed it.

Gaining mpgs with taller tires and gears works by balancing the taller tire by putting it back in its sweet spot with the new gearing. At least that's how I see it.

 

[HARDTRAILZ]

Gear Ratio Guide
When ever you change tire size from the original size to another there will be a direct effect on power and drivability. We have developed this chart to help you select the optimum gear ratio to put your performance back where you want it.

Using the chart below, first determine your original gear ratio and tire size and follow to the intersection that should be your approximate RPM at 65 MPH. Next find your new tire size and follow that across to the closest RPM to your original and that will be first choice.

If you are interested in a change that will give more power or better fuel mileage use the color coding as a guide.

• Highway Driving, Good Fuel Economy--BLUE
• Daily Driver, Best Overall Performance--GRAY
• Most Power and Towing, Reduced Fuel Economy--YELLOW

This chart is based on 65 MPH and a gear ratio of 1:1, on a manual transmission in 4th gear.

Note: If you have an automatic transmission your RPM will higher due to slippage in the transmission and the torque converter. With an overdrive transmission your RPM in overdrive will be 15% to 30% less than indicated.

 

[xavierny25]

According to the info @HARDTRAILZ posted and checking in more detail with my current wheel and tire set up I can live with the slightly higher rpm and mpg loose.

 

[HARDTRAILZ]

FYI the 4l60 is like a 0.7 overdrive ratio so RPM are lower. But it is a good basic guide for how things are affected

 

[Sparky]

Also something worth noting is in OD the TCC should be locked so there is next to no RPM slippage. Pretty much any modern auto trans does that... not sure why that chart does not mention a torque converter clutch.

I saw a similar chart at one point a while ago that was set up for an overdrive gear. I'll have to see if I can find it...

 

[HARDTRAILZ]

I think the chart I posted is OLD and its from a 4x4 place that is far more manual or turbo 400 type supported