Offroad Trailblazers and Envoys

4.56 gears and ABS

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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.
Facebook groups are useless...
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