Offroad Trailblazers and Envoys

4.56 gears and ABS

G80, GU6, GT4, GT5, WTF? This section is for gearing and driveline stuff.

by AzEric » Fri Jun 28, 2019 12:14 pm

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!
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by Trail X » Wed Jul 03, 2019 11:01 am

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?
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by Tricguy007 » Wed Oct 16, 2019 12:27 am

I just changed gears 3.42 to 3.73 with a 31.5" tire my abs still works fine but lost my cruise control
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by AzEric » Wed Nov 06, 2019 10:28 am

Apologies, James. Haven't logged on in a while, was trying out the Facebook group as a method of knowledge transfer. :lol:
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.
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by gtblazer » Tue Nov 03, 2020 12:35 pm

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,
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by AlekG » Fri Feb 12, 2021 12:56 am

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

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