4.56 gears and ABS

[AzEric]

My 2004 truck originally had 3.73 gears, and when I toasted the transmission oil pump and had to rebuild I decided to swap to 4.56 gears to match my 33 in Yoko MTs while it was down. I was well aware of the fact that this might cause issues with the ABS system from reading around this and other forms about the swap (i.e. https://gmtnation.com/forums/threads/ab ... wap.14024/) but I am possibly going to go to 35s in the future, and didn't want to have to do gears more than once. I am simply posting this as an update from most of the other articles, dated back in 2015. During gear break in on my truck, the ABS/brake codes set as expected. I used the sps system to update the software on all of the computers in the vehicle to the most current rev, and then used a Tech II to update my tire size to 285/75R16 LT. That's it. ABS issue has not returned. Going to verify the speedo with GPS today, but cruising in traffic I was reading about correctly if you consider most people drive ~5 over around here.

Cheers!

[Trail X]

I'm not sure I follow Eric. I've had this issue for years now, and I just unplug my abs fuse to keep the dumb alert from scaring the hell out of me every time I drive. What is the sps system you refer to? I can't imagine updating tire size would fix the ABS issue entirely, because it would not take into account the new ratio of rear ABS sensor to front ABS sensor due to the gear change. Can you explain further?

[Tricguy007]

I just changed gears 3.42 to 3.73 with a 31.5" tire my abs still works fine but lost my cruise control

[AzEric]

Apologies, James. Haven't logged on in a while, was trying out the Facebook group as a method of knowledge transfer.
The sps system is the third party software that can install new revs of the computer firmware that the shop I was having my 4L60E repaired at uses. All we did was update all the firmwares, and then used the tech II to input the tire size I am running. This fixed the ABS from triggering the alarm due to it bringing it within the margin of error allowed by the pcm. I still haven't set the ABS alarm since doing so. The speedo is off, though, as expected, so my cruise won't work above 43mph. Still working on a way to edit the parameter for gear size in the pcm.
Facebook groups are useless...

[gtblazer]

Hey, I'm pretty new to the forum and have been doing a lot of reading here and I can tell that changing the gears out in our older TBs will mess with the ABS. I have the 3.73 in my TB and am interested in going to the 4.11 which sounds like it will work but the 4.56 won't. I'm not even sure if a 4.56 is even an option with the 8" rear end so may be a moot point for me. Before I commit though, just wanted to see if anyone has figured out how to put a 4.56 in an older TB and get the ABS to work correctly.

Thanks,
Brian

[AlekG]

Hello everybody. Its been a looooooooooong time since I have contributed anything here (due to life circumstances). But I'm glad to say that my rig is still around, doing well, and in storage for now.

So here's some comments on the thread. I apologize if I am stating something obvious ... just a bit rusty.

There was (and still is to my knowledge) no 4.56 solution for the 8" rear end. That is why I swapped mine to a 8.5/8.6 inch rear end from an auto reclamation yard. You have to be careful though as there was a switch from a single sensor to dual sensor ABS for the rear on the 2005? model (could be off on the year). So you have to match the version to your vehicle or there is no way to plug in the sensor lead and the ABS light will be on permanently.

The good news is that Yukon Gear still has the 4.56 ring/pinion for the 7.2 inch front diff so you are covered if you go 4.56 on the 8.5/8.6 rear end.

As for the computer / speedo / ABS / etc. I used the HP Tuners product to change the settings for the tire size and gear ratio and that has kept everything nice and happy.


Will try to get back into this as I have some plans for additional mods this year. I have some parts sitting there and ready to go but there is a specific roadblock for me in my front suspension which has to be addressed first.

Alek

[larryk]

I went from 3.42 to 4.10 in my 2004 6Cyl, and it was a MESS. The ABS, as you note, reads wheel speed through a calculation from the output shaft speed from the trans/transfer case, and the hubs in the front....obviously AFTER the other side of the gearing. Changing tire size has zero impact on it, but changing gears....wellllll.... The solution for me, after trying the HPT method (which didn't work) was having a PCM programmed with the "C" version of the operating system. Its actually hardcoded in the OS and not part of the calibration file.....totally dumb, but it is what it is. GM has three version of the OS...A for 3.42, B for 3.73 and C for 4.10. Changing the OS in the PCM completely solved the ABS and Cruise issues. 100% back to working perfectly.

FWIW, if I recall the the 2006+ versions have 4 channel ABS (the rear axle has sensors on the outer axle tubes in the back), so you can update via HPT for speedo calibration...but the ABS and cruise should work fine as you are measuring axle speed on all wheels post gears.

[AlekG]

The solution for me, after trying the HPT method (which didn't work) was having a PCM programmed with the "C" version of the operating system. Its actually hardcoded in the OS and not part of the calibration file.....totally dumb, but it is what it is. GM has three version of the OS...A for 3.42, B for 3.73 and C for 4.10. Changing the OS in the PCM completely solved the ABS and Cruise issues. 100% back to working perfectly.

Wow, I wasn't aware of the hard coding of the gear ratio on our PCMs. But it got me thinking back to tuning my PCM. I am almost 100% certain I used PCMofNC for the initial performance tuning and tire size change. I was confused with another company called PCMforLess but I don't think they are active anymore. There was some kind of relationship there back in the day but I don't remember the specifics.

So PCMofNC were the ones who really helped me out in a jam. After swapping my stock PCM for their tuned one, shipping it back, and getting the HP Tuners kit, I did the axle mods with 4.56 gears. So using HPT, I saw that it let me change the gear ratio in the software and when it was time, I was foolish enough to use a laptop where the battery was suspect and during the PCM write, the laptop died

I was basically dead-in-the-water a few days before an offroad event I was planning to attend. I contacted PCMofNC with the emergency and they graciously sent another tuned PCM (with the 4.56 gear ratio) and charged me only the shipping costs as long as I sent them the dead PCM.

So I am wondering if the tuners figured out a way around the hardcoded A,B,C OS versions and provide an "open" OS version when you buy theirs. I would think that is the only way they can sell their tunes if someone wants gear ratios outside the factory ones.

Afterwards (with a good laptop ) I checked on the settings with HPT and saw that the gear ratio was still editable and backed up the complete tune.

FWIW, if I recall the the 2006+ versions have 4 channel ABS (the rear axle has sensors on the outer axle tubes in the back), so you can update via HPT for speedo calibration...but the ABS and cruise should work fine as you are measuring axle speed on all wheels post gears.

Yes, either in the 2005 or 2006 year they switched to 4 channel ABS which is why you have to pay attention to the year of the axle if upgrading from the 8"

[larryk]

Exactly! You have a 2006, so yes, you can change the gear ratio using HPT successfully. Those of us with the older trucks, ie up to 2005, CANNOT change gear ratios AND ensure the ABS/Cruise works properly. I think for Tuners, and I know I can with my GM programming tool, change the operating system in the PCM to whatever version. But, you cannot change the OS with HPT. ALso, since you are stuck with the GM OS, you are also stuck with the GM ratios....3.42, 3.73, and 4.10 ONLY. Use any other ratio, and the ABS and Cruise will not work.

Finally, your comment on axle years.... You CAN swap ANY year axle into an older truck, but you can ONLY swap a 2006+ axle into a 2006 4channel ABS truck. I have a 2004 with a 2007 SS 9.5" rear with the G86 Posi. Of course all SS's came with 4.10....so this is what I wanted, and when I swapped out my front diff, found all the fun of the GM operating system shenanigans. LOL

FWIW, PCMofNC was the same company as PCM for Less. I also found that Westers Garage (some place in Canada) had some great tunes for the GM360 platform as well.

The solution for me, after trying the HPT method (which didn't work) was having a PCM programmed with the "C" version of the operating system. Its actually hardcoded in the OS and not part of the calibration file.....totally dumb, but it is what it is. GM has three version of the OS...A for 3.42, B for 3.73 and C for 4.10. Changing the OS in the PCM completely solved the ABS and Cruise issues. 100% back to working perfectly.

Wow, I wasn't aware of the hard coding of the gear ratio on our PCMs. But it got me thinking back to tuning my PCM. I am almost 100% certain I used PCMofNC for the initial performance tuning and tire size change. I was confused with another company called PCMforLess but I don't think they are active anymore. There was some kind of relationship there back in the day but I don't remember the specifics.

So PCMofNC were the ones who really helped me out in a jam. After swapping my stock PCM for their tuned one, shipping it back, and getting the HP Tuners kit, I did the axle mods with 4.56 gears. So using HPT, I saw that it let me change the gear ratio in the software and when it was time, I was foolish enough to use a laptop where the battery was suspect and during the PCM write, the laptop died

I was basically dead-in-the-water a few days before an offroad event I was planning to attend. I contacted PCMofNC with the emergency and they graciously sent another tuned PCM (with the 4.56 gear ratio) and charged me only the shipping costs as long as I sent them the dead PCM.

So I am wondering if the tuners figured out a way around the hardcoded A,B,C OS versions and provide an "open" OS version when you buy theirs. I would think that is the only way they can sell their tunes if someone wants gear ratios outside the factory ones.

Afterwards (with a good laptop ) I checked on the settings with HPT and saw that the gear ratio was still editable and backed up the complete tune.

FWIW, if I recall the the 2006+ versions have 4 channel ABS (the rear axle has sensors on the outer axle tubes in the back), so you can update via HPT for speedo calibration...but the ABS and cruise should work fine as you are measuring axle speed on all wheels post gears.

Yes, either in the 2005 or 2006 year they switched to 4 channel ABS which is why you have to pay attention to the year of the axle if upgrading from the 8"

[AlekG]

Man ... it was so hit-and-miss back then.

If I remember correctly, first, I didn't research the ABS switchover at all and got an earlier rear end because I found a really cheap one (compared to any 2006+ I could source at the time). So when the shop installed the 4.56 gears into the axles they brought up the issue of the rear not having the connections for the ABS leads The solution at the time was a piece of black tape over the ABS light

I'm pretty sure I did the whole Big Western Trip like that ... no ABS. It was about a year later that I found a 2006+ axle for a decent price and got it swapped again.

And with the tuned OS, I had no idea of the pre-2006 restrictions. PCMofNC just said they can program any gear ratio and when I told them I was going to change gears later, they suggested HPT so I could do it myself.

So what you are saying (for my clarification) is that for a pre 2006, PCMofNC could not do a tune that included a 4.56 gear ratio? If that's the case then I really lucked out back then when I ended up finding the very low km, GM exec-only driven 2006 LTZ on a Chevy lot in Listowel, Ontario. A tiny farm community about 1:45 from where I lived at the time. I checked on Google, that dealership is still there ... good for them!

[cbassila]

Hello Everyone. Are we saying that there will be no way to install 4.56 gears on a 2002 trailblazer and make the ABS and cruise control work?

[xXxSilveradoxXx]

I've got 4.56s on my 2004 and the cruise control and ABS work. I used EFI Live for tuning.