05GTO6.0

Last july I had my diff gears changed from the stock 3.46's to some 3.90's. Ever since then the speedometer has been off. This was to be expected, but when I took it in to get it tuned I was told that there was no way for them to tweak the speedometer in the 05 because the gauge cluster was somehow a separate unit from the ECU, so changing the ratio in the ecu didnt change the physical speedo. Yesterday I caved in and decided to take it to a dealership (I was told they were the only people that could do it because you needed codes from GM or something) but they told me that they were unable to change it. I know I'm not the first GTO owner to ever put 3.90 gears in their car, how did you guys adjust the speedometer? I dont want to be stuck with 58 meaning 45 and 80 meaning 60 forever..

GotToGo

I used HP Tuners.

VZClustermod will work too.

05GTO6.0

The tuner I use uses HP tuners and said that when he changes the speedo calibration it will change in the ECU, and it will show the accurate speed on the HP tuners program when you read it, but nothing changes on the actual cluster. Ive looked into VZClustermod for the shift light activation and whatnot, but I haven't found a way to adjust the speedo with that program. I found an archived thread on ls1gto over the speedo issue but the thread did not include a solution. Apparently the speedo problem only happens on the 05 and 06 models, and not the 04 for whatever reason

GotToGo

I'm pretty sure your tuner is just missing something. But, I have to admit I have never changed it on an 05/06. I suggest you post the question on the HPT forum and see what happens.

As for the VZClustermod, go on LS1GTO and contact Vending1337 directly. I'm sure he can tell you. Or post in the VZClutermod thread.

http://www.ls1gto.com/forums/showthr...7#post20498057

GotToGo

Take a look at this.

http://www.hptuners.com/forum/showth...oblem-w-3-91-s

dw456post

I have changed to a 4L80 with different gears and mine reads correctly after I changed the calcs in HPTuners. When you change the rear ratio and click commit, there is still some cleanup that you have to do in the shift tables. Maybe he doesn't want to spend the extra time it takes. If you don't have the program, it is hard to help you. In VZ Clustermod, you have to change the number of pulses to get the speedo to adjust. Use your GPS and keep adjusting.

05GTO6.0

Got my aldl cable today and was able to use the pulses per kilometer setting in VZ Clustermod to fix the speedo! Also you get to enable the factory shift light and for a $65 cable being the only investment I'm very happy with it. Thanks for the help!

GotToGo

Good job!