Changing gear ratios on the I6

[Shdwdrgn]

I have a 2004 Trailblazer with 3.42 gears. I am in the process of swapping to 4.10 gears, and I'm wondering if anyone can tell me if there is anything I can change with HPT to update the computer?

If not in HPT, any suggestions what needs to be updated? My dealership said nobody there has ever made this kind of change before, so they didn't know what would need done.

[Russ K]

4.10/3.42=1.1988, then multiply the VSS Pulses per mile, the VSS Trans Revs per Mile and the Trans Revolutions/Mile fields by 1.1988. Also multiply all your trans shift speed & TCC lock/unlock speed tables by .834.

Russ Kemp

[Shdwdrgn]

Thanks for jumping in. Adjusting the settings under Speedo makes sense, but I don't follow why the shift and lock tables would have to be adjusted afterwards... If the first settings were already changed, I would think this would calibrate everything else back into the original ranges?

I'm also curious if your method has any affect on the actual speedometer speed shown, since I've never found a way to successfully adjust that for my oversize tires. Rear axle is going in on Saturday, so I'll have plenty of time to play with HTP settings after that.

[Shdwdrgn]

Erg... I just realized I posted in the V6 section rather than under I6.

[Shdwdrgn]

Well, the changes had no effect on the speedo or odometer, but it seems like it is shifting at about the right range. I also had to soften up my shift times because it was hitting the gears hard, even at light throttle in town.

The REAL problem now is that I am continually getting dash warnings for the abs/brake system, and I got error codes for P0741 (TCC system stuck) and P0894 (Trans component slipping) after driving around for about an hour. Any suggestions?

[Shdwdrgn]

Just an update here... Both the front and rear differentials have been replaced with the 4.10 gears now, and I continue to get abs/brake system warnings every time I cruise at a constant speed for a few minutes. There have been no further CEL codes coming up, but the ABS system is definitely a problem, especially with Winter coming soon.

I've been making calls to dealerships and off-road shops in the area. Nobody seems to know how to reprogram the system for the new gear ratio. ANY help would be appreciated!