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Regear and tune

chrislcrews

By chrislcrews
in Modifications & Accessories

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chrislcrews Enthusiast

chrislcrews

Posted
Posted

Hey guys so I have a 6 inch lift and 35s

 

Truck is a 2015 4x4 z71 slt GMC Sierra unsure what hears I have currently but was told but a guy at work that if I want my transmission to last I should regear my truck. Question is with those tires and lift, what ratio should I go for and should I tune it after?

 

Thanks!

brad519 Enthusiast

brad519

Posted
Posted

If you have a 2015 3/4 ton gas engine, it should have 4.10 gears in it. I'm no pro but my 2500 with 4,10 turn my 34.6 with no problems. Someone else may chime in but I don't think a 2500 needs new gears running 35's. Now my 1500 I had with 35's I regeared to 4.88.

chrislcrews Enthusiast

chrislcrews

Posted
  • Author
Posted

Yeah sorry I have A 1500 haha. Forgot that!

 

 

From what I saw in the web people say 4.56 if I do highway to keep mpg but 4.88 for city.

 

I live in a beach town that's also country I do a lot of highway driving and off road and city driving so would the best combo be 4.10?

SouthpawHD Enthusiast

SouthpawHD

Posted
Posted

You should slide over to the 1500 section of this website, you'll get more responses.

 

EDIT: I guess the powers at large moved it for ya.

GRN69CHV Enthusiast

GRN69CHV

Posted
Posted

Going to 35" tires, you only increased tire size by 10%, if truck had 3.42 gears [you really need to find this out, odds are good that having been ordered with the Z71, they checked the 3.42 rear axle box on the order form], the only option to fit that housing without having to get a new carrier and adapting parts is a 4.10 gear set. 4.10's would be a 20% increase in gearing over stock, but net 10% increase in gearing with the larger tires which should work out nicely.

chrislcrews Enthusiast

chrislcrews

Posted
  • Author
Posted

Oh okay. Well do you guys think re hearing the truck is worth voiding the warranty, I mean it being lifted already voids it some I am assuming.

 

If 4.10 is all I can go too. I'm fine with that but even with driving highway. I assume my Rpm will ramp up to 2k?

 

All info regarding this is helpful as I am a noob when it comes to this kinda thing.

 

Anyone here have 4.10 gears and suggest still going this route?

arcasey Enthusiast

arcasey

Posted
Posted

Oh okay. Well do you guys think re hearing the truck is worth voiding the warranty, I mean it being lifted already voids it some I am assuming.

 

If 4.10 is all I can go too. I'm fine with that but even with driving highway. I assume my Rpm will ramp up to 2k?

 

All info regarding this is helpful as I am a noob when it comes to this kinda thing.

 

Anyone here have 4.10 gears and suggest still going this route?

 

The only portion of your warranty that is voided is anything that has been replaced. They can't just take your entire warranty away. They won't cover anything that has been modified from stock or that they can prove malfunctioned due to the aftermarket parts.

 

With that said, your truck, unless it has the max trailering package should have a 3.42 rear end. Assuming this, the way to find out what your new ratio should be to keep stock performance is:

[(New Tire Diameter)/(Old Tire Diameter) ] * Old Ratio = New Ratio. Your truck likely came with P265/65R18 (31.6") or P275/55R20 (31.9") tires. Just for example let's assume you have the 18" rims which would mean you have 31.6" Diameter tires. Your new ratio to keep stock performance will be: (35)/(31.6) * 3.42 = 3.79.

If you have the 20" rims then the new ratio would be 3.75. In all honesty, you would probably be alright going to a 3.73 (a standard GM ratio that you may be able to install without harming your warranty) and your performance and fuel economy wouldn't change all that much. It WILL change though, mainly due to the heavier weight of the bigger tires. The max that I would go would be 4.10's. Much past that you'd be able to pull the world but your fuel economy would be crap.

 

Here is another thread where this was discussed extensively:

http://www.gm-trucks.com/forums/topic/189486-regearing-truck-after-lift-kit-and-35s-tire/

GRN69CHV Enthusiast

GRN69CHV

Posted
Posted

Manufacturer for the current 9.5" rear is AAM, they don't make a 3.73 that Installs on stock carrier in that housing Option is 3.42 or 4.10. To confuse the issue, GM offers 3.73 with Max Tow, it does use stock carrier, but housing is different. My guess is housing is machined deeper at pinion support to accomodate the larger ring gear

Matthew Kashima Enthusiast

Matthew Kashima

Posted
Posted

I have a 2014 Silverado and recently swapped to 4.10s from 3.08s and I am running a 305/55/20. The 4.10 is perfect for a 33 and has my RPMs around 2k at 75mph. I would suggest 4.56. On a side not my MPGs went up to an average of 15+ and i have a heavy foot. Good luck

GRN69CHV Enthusiast

GRN69CHV

Posted
Posted

I have a 2014 Silverado and recently swapped to 4.10s from 3.08s and I am running a 305/55/20. The 4.10 is perfect for a 33 and has my RPMs around 2k at 75mph. I would suggest 4.56. On a side not my MPGs went up to an average of 15+ and i have a heavy foot. Good luck

 

When you did the gear swap, what did you do for a carrier? Did you do the Yukon setup using the earlier 9.5" gear set with the adapter yoke,etc or did you get a stock GM carrier and use the AAM gears? I believe you also had to replace the complete front 8.25" assembly?

chrislcrews Enthusiast

chrislcrews

Posted
  • Author
Posted

I'm going to check my truck to see what hears it has in it when I get off work and I can post you guys what I found. I can't remember if I have the max tow package or not.

 

What is te code I'm looking for to know what's heard I have? Is the info located in the glove box or door seal?

 

 

Thanks!

arcasey Enthusiast

arcasey

Posted
Posted

Manufacturer for the current 9.5" rear is AAM, they don't make a 3.73 that Installs on stock carrier in that housing Option is 3.42 or 4.10. To confuse the issue, GM offers 3.73 with Max Tow, it does use stock carrier, but housing is different. My guess is housing is machined deeper at pinion support to accomodate the larger ring gear

 

Ah, I did not realize they were so different, thanks for the info as I was contemplating doing this in the future. I have read a few other threads and just want to make sure I understand but basically what I have gathered from it is that it is just a clearance issue with the stock housing, is that correct? I can't believe GM wouldn't have tried to standardize the housing so that all factory options would work.

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