Change Rear Gear Ratio?

[beerjay]

Is it feasable to change the gearing on the rear of a vehicle by a setting in the truck? Without a major overhaul of the drive train.

Fact or fiction?

I had heard there may be some options using the maintenance settings on the vehicle computer interface. My Suburban has a 3.43 rear end and would likely benefit greatly by changing it to 3.73. The Tow/Haul and Manual shift limiters do help with adjusting the shifting up and down but hills take me into 3500 rpm territory.

[raspivey]

I don't know of any vehicle you would want to tow with that has electronic differential switching. I think they're playing with it in some all wheel drive and electric cars. Generally, the only way to do that is to physically change the gears. 3500 rpm isn't too bad. As long as you're not overheating, you'll be ok. Change the fluids more often. I considered a gear swap in mine, but for around $1200 I decided it would take too long for it to pay for itself with no more towing than I do in a year.

[wyo700]

Originally Posted by beerjay

Is it feasable to change the gearing on the rear of a vehicle by a setting in the truck? Without a major overhaul of the drive train. Fact or fiction? I had heard there may be some options using the maintenance settings on the vehicle computer interface. My Suburban has a 3.43 rear end and would likely benefit greatly by changing it to 3.73. The Tow/Haul and Manual shift limiters do help with adjusting the shifting up and down but hills take me into 3500 rpm territory.

You spinning 3500 Rpms is nothing for that engine. And although changing gearing would help I also have to say the 5.3 also may lack the power to stay in the lower Rpms. Diesels are made for low end torque and will stay in low rpm while towing. Gas engines have a higher rpm torque curve. My tundra 5.7 peak torque is at 3500 rpm and when spinning at that rpm is a monster when towing. I have no problem pulling long hills and have more power to spare. If all you are doing is hitting 3500 or even 4000 you will be fine.

[Twisty]

Look up the horsepower and torque curves for the engine.
Find out where PEAK HP and PEAK torque are produced.
It is common for a gas V8 to produce the most power at 4200 to 5800 RPM's.
Don't be afraid to let the engine spin.
Every gas engine has an RPM when working when it "sings".
Pull a hill and you'll find it.
You might be in 3rd at 4200 RPM running at 58 MPH or you might be in 2nd spinning 5300 RPM at 62 MPH.
The 5.0 in my truck thrives at 3500 to 5500 RPM. You ought to hear it on a hill in 2nd gear running at 58 MPH when pulling 6200 lbs.
I am going to miss it.

[youroo]

Originally Posted by beerjay

Is it feasable to change the gearing on the rear of a vehicle by a setting in the truck? Without a major overhaul of the drive train.

Fact or fiction?

I had heard there may be some options using the maintenance settings on the vehicle computer interface. My Suburban has a 3.43 rear end and would likely benefit greatly by changing it to 3.73. The Tow/Haul and Manual shift limiters do help with adjusting the shifting up and down but hills take me into 3500 rpm territory.

You have (2) Differentials to change gears in your 4x4. Cant just change (1). Youroo!!

[John4th]

Correct on all! Gas engines are a higher RPM for torque. My 5.7 in my Tundra will sing to me at 3000 RPM when pulling up a steep grade, but it's suppose to do that. Changing gearing will not let you run RPMs like a diesel. It's a little nerve-racking if you're not used to it. Seems like it's going to shoot up through the hood. As long as it's not over heating (again, gear changing will not eliminate that either), it's doing what it's designed to do.

[beerjay]

Thanks for the informed insight folks!

I expected the change was a mechanical refit not settings.

The high RPMs are a bit unnerving when you are not used to the noise, glad its just doing what its supposed to!

[EXGMTech]

if it's crazy loud you may have a stuck fan clutch...my Duramax fan is quite loud when it kicks in.

[SaskCampers]

Originally Posted by beerjay

Thanks for the informed insight folks!

I expected the change was a mechanical refit not settings.

The high RPMs are a bit unnerving when you are not used to the noise, glad its just doing what its supposed to!

So are you under the impression going to 3.73's will cut your RPM's from the 3500 you are seeing when you hit hills? If so you would be surprised as 3.73's will increase your rpm's to probably in the neighborhood of 3800 or so. You would have to go the other way down in gears to slow the engine down. Going to 3.73's will give you more pulling power off the line and keep you higher in RPM's where your engine makes it's power whel pulling in the hills and slower gears like 3.25's will give better economy at the cost of pulling power. Hope this helps you understand what gears do a bit better.

[beerjay]

Sorry for muddying my own water ... towing vs. rpm.

Would the 3.73 increase tow capacity and make the pull easier?

The RPM was an observation that seems to be par for the course with a 'gasser'. So I had 2 issues but they may be related, and as The Sasks said, the 3.73 would require more RPM for the same speed.

[raspivey]

It will pull somewhat easier. You're trading low end torque for high end speed. Depending on a lot of variables, you'll see some improvement when starting from a roll and accelerating (and fuel economy to go along with it). You'll also see some (again, depending on a lot of variables) loss of fuel economy when you aren't towing...probably not noticeable in city driving and more pronounced at highway speeds. Honestly, if you're only pushing around 3500 rpm when climbing, I'd just continue to downshift and roll with it. It doesn't sound like it's really struggling and you'll likely only get about 2 mpg or so by swapping (while towing). Consider how long it would take for that to pay for itself based on how much you pull with it. Will it improve your towing?...probably. Is it worth it?....depends on your situation. If you have 4WD, double the price.

[EricInColorado]

Engines are tested at their red-line for hours and hours. 3500 rpm is nuthun'