FireEMT978

Hey all,
Curious as to any idea how or where I can get the speedometer calibration done on my 2014 Express 2500LT 6.0?
My rear end shattered. And due to COVID supply issues, the shop ended up having to change the ratio from 3:42, to a 3:73. Now, my speedo is off by 9-10%. Hypertech does not have one that will work with the Express 2500. GM dealers can't touch it.
Thanks

mountainmanjoe

let us know when you find out. As far as I know it would require custom PCM reflashing. Sounds expensive. How did you shatter the rear end?

FireEMT978

Even though the fluids were all changed on schedule. I was on the highway, and it felt like the rear end tried pole vaulting. Broke a gear in half. Then that decided to bounce around in the carrier and pinion. Really ugly. The shop kept getting the wrong parts shipped due to COVID supply issues. Ended up going from a limited slip 3:42, to a Posi 3:73. Which, I actually like a LOT better. No doggie acceleration, and tows much nicer. But, now my speedo is 9% off, it is racking up miles on the odometer that much faster, and my fuel range is screwed up.

og52

I've been through this on my Silverado. Replaced the 3:23 with 3:73 gears for trailer towing. Dealers refused to work on it and the various programers didn't work. Ended up having a local speed shop flash the computer. They had a specialized program that addressed this problem.
For my Silverado the VSS measures transmission output speed which sends a signal not only to the speedometer but to the anti-lock brakes. Usually not a big deal to alter the VSS signal but there is an additional speed sensor at the input of the transmission. The two sensors work together to determine transmission slippage. If the VSS signal is altered to calibrate the speedometer the computer will throw a code for transmission slippage. Big headache that was finally resolved by custom programming.
Altogether it cost me about $200 for labor and program licensing fees

MiragePilot

I just went through this issue (as a result of oversized rims and tires) and here is a summary of the solution:

1) Don’t waste your time going to a GM dealer for help. If you have non-GM rims (or differential) on your vehicle they will NOT help you, period. The Explorer van conversion company built my conversion van and put larger than OEM rims/tires on the van. They also put a new/updated data label on the driver’s door jam which indicated the new, larger wheels and modified inflation pressures. That update was still not sufficient for GM to help fix the issue.

2) In order to update the vehicle control system with a new/different wheel size (or differential ratio) the updated wheel size (and/or differential ratio) info has to be programmed into BOTH the ABS controller (EBCM) AND the engine PCM.

3) The EBCM update can be made with a decent vehicle scan tool, but the PCM update requires an engine tuning device to reprogram the PCM.

4) In order for the speedometer to read correctly, and the transmission shift speeds/points to be correct, the PCM has to be updated. Updating just the EBCM will have no effect on the speedometer reading and transmission shift points.

I was able to find an independent auto electrician/diagnostic pro to successfully complete this update, and now all is good.

Peter

mountainmanjoe

Could you guys post the names/locations of these businesses please?

MiragePilot

The guy that did my ECM reflash was based in Tucson, AZ. If you are based Tucson, ping me and I’ll give you his contact info.

Peter

og52

JBA San Diego

https://jbaspeedshop.com