Offroad Trailblazers and Envoys

Changing my 3.73 to a 4.11

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

by gtblazer » Sat Nov 07, 2020 6:40 pm

Hi, I'm new here and finally thinking about doing some work on my TB after all these years. I was hoping to confirm a couple things before I look at changing my gearing from 3.73 to 4.10/4.11 which I need to do to pull a trailer better with the larger tires I put on it several years back. After doing a lot of reading, it looks like you can't get a 4.56 gear for the 8" rear end and I just wanted to confirm that. It also sounds like even if I did that the ABS wouldn't work right unless someone has finally figured out the secret to how it's coded in the ECM.

The 7.2 diff on the front seems to be a lot easier to find gears for than the 8.0 rear but I think I've found the 4.11 for the rear for about $200 and the front end for about $160, does that sound right or has anyone found them cheaper somewhere? I know you can swap the rear out but I've already got the G80 and had all the seals and bearings in the rear of my TB replaced not too long ago so I think it would be kind of a waste to do that.

Thanks,
Brian
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by Diacom » Mon Nov 09, 2020 9:17 pm

Price may be ok, hard to compare as I upgraded an 8.6" rear so not necessarily a direct comparison as supply and demand come into play. As long as your good with the G80 and 4.11 gears there isn't a need to jump to an 8.6" diff unless you want to go to 4.56 gears. I wouldn't re-gear your current if you planned that option.

There was someone on here that had the vin available for a 4.10 geared vehicle that would help keep your 4.11 working with the ABS. It may take some digging to find it though, been a few years.

So if your good with keeping the 8.0 and can get matching ratio's for front and rear, that price doesn't appear to be terrible. You can always shop around and find lower if you look hard enough, but that depends on the time you want to spend.
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by gtblazer » Tue Nov 10, 2020 7:54 am

Thanks, I appreciate the help. I'd love to have the 4.56 but I don't want to give up ABS to get it so I think I'll just stick with the 4.11. I've seen the postings about using the VIN to reset the computer for 4.11 and I'll see if I can work through that if I have trouble with the ABS. It sounds like you definitely do if you start with the 3.42 but I think I recall some people having luck with going from 3.73 to 4.11 without ABS freaking out.
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by Diacom » Tue Nov 10, 2020 11:17 am

I don't believe the Vin was used to work around an ABS issue, but to help with the speedometer iirc. I think you will be ok ABS wise even with 4.11's. Either way it'll be good to know that the option is there if it's needed.
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by gtblazer » Sat Nov 14, 2020 6:55 pm

Cool, thanks again for the help. About time to order some parts and get to work.
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