Re-gear and Detroit Locker in a 2017 2500HD 6 Liter

SierraHD17 · December 24, 2017

13 minutes ago, sdeeter19555 said:

I knew something had to be changed, but it was my understanding that it was a "check box" and you were limited to factory gear options...

Steve
2012 2500hd 6.0l

If that were the case everyone changing tire sizes would be screwed too... But you aren't. There are lots of newer trucks now with 4.56 or deeper out there as gears became available for the half tons. It's not tough to change in the tune. I would say 3/4 tons which holds true for Duramax guys... but nobody regears the gas ones... Just complain about the stock ratios instead lol.

Edited December 24, 2017 by SierraHD17

Big Whiskey · December 24, 2017

In for the updates!!

rocnrol · December 28, 2017

The axle reduction ratio has to match what the pcm is expecting the ratio between transfer case out put and wheel speed. It's not hard to adjust with the software. I drove my AVY a little bit after going from 3.73 to 4.10 without re-flash. About 5 miles from a start-up it would disable traction and stability because the transfer case was reporting too many revs for wheels.

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Using that logic, then why isn't my truck having a fit because of my larger tire? The reason I had mentioned going to a 4.56 ratio is that running a 35" tire, the math works out that, that ratio will bring the truck to an overall ratio the same as stock.

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XSKIER · December 28, 2017

Wheel speed sensors on the axle shafts read rpms. Those rpms are then factored by the revs per mile of the installed tires for the speedo display. While your speedo display may be correct, if you don't re program the pcm you'll get stabilitrak errors. Even if you don't care, the pcm needs to know the ratio between the transfer case output and the wheel speed not observed vehicle speed.

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SierraHD17 · December 28, 2017

Shift points in the trans won't be right either as they are speed based. Its a bit of changes to make but it's not difficult at all.

gearheadesw · December 28, 2017

Had 35 inch tires on the last truck, no issues in 25 k miles, no reprogramming of anything. I think you're over thinking it.

8 hours ago, XSKIER said:

Wheel speed sensors on the axle shafts read rpms. Those rpms are then factored by the revs per mile of the installed tires for the speedo display. While your speedo display may be correct, if you don't re program the pcm you'll get stabilitrak errors. Even if you don't care, the pcm needs to know the ratio between the transfer case output and the wheel speed not observed vehicle speed.

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sdeeter19555 · December 28, 2017

Had 35 inch tires on the last truck, no issues in 25 k miles, no reprogramming of anything. I think you're over thinking it.

35 inch tires aren't much of a change from factory. The truck doesn't know about the actual ground speed, only what it calculated based of RPM and speed sensors.

Steve
2012 2500hd 6.0l

XSKIER · December 28, 2017

2 hours ago, gearheadesw said:

Had 35 inch tires on the last truck, no issues in 25 k miles, no reprogramming of anything. I think you're over thinking it.

You didn't re-gear your last truck, no problem.

SierraHD17 · December 28, 2017

How about you guys just let me do it and I will give you a step by step lol. This isn't my first re-gear either but it is my first on an E78 ECM.

gearheadesw · December 28, 2017

Not trying to start a fight, but what is the difference if the drive shaft is slowed, or sped up, by different tire sizes or a re-gear. I had a %10 difference in speed verse speed readings on the speedometer. 4.10:1 to 4.88:1 is what, a %20 difference, I can see how the computer would get confused.

rocnrol · December 29, 2017

Wheel speed sensors on the axle shafts read rpms. Those rpms are then factored by the revs per mile of the installed tires for the speedo display. While your speedo display may be correct, if you don't re program the pcm you'll get stabilitrak errors. Even if you don't care, the pcm needs to know the ratio between the transfer case output and the wheel speed not observed vehicle speed.

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My speedo isn't correct.... Because I have taller tires..... And my truck isn't having a freak out.

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rocnrol · December 29, 2017

How about you guys just let me do it and I will give you a step by step lol. This isn't my first re-gear either but it is my first on an E78 ECM.

I'm with you. And waiting with great interest

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4wdriver · December 29, 2017

10 hours ago, rocnrol said:

My speedo isn't correct.... Because I have taller tires..... And my truck isn't having a freak out.

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Mine either but my shifts are definitely different.

SierraHD17 · December 29, 2017

Shifts are speed based so if you have the stock tune and larger tires they will occur differently because your vehicle speed is wrong and your shifts are based on that speed. Even correcting the speedo does not correct the shift speeds as they will still be the stock speed values. If you wanted the shifts at the same rpm as stock you have to change them too. And honestly the stock shifts in these things are way too early anyway lol.

4wdriver · December 29, 2017

38 minutes ago, SierraHD17 said:

Shifts are speed based so if you have the stock tune and larger tires they will occur differently because your vehicle speed is wrong and your shifts are based on that speed. Even correcting the speedo does not correct the shift speeds as they will still be the stock speed values. If you wanted the shifts at the same rpm as stock you have to change them too. And honestly the stock shifts in these things are way too early anyway lol.

I agree about the stock shifts. The shifting is the one thing I liked better in my 02 hd, that tranny was predictable and always reacted the same. I just might look into some tuning next summer.