Tech2Win can't correct inaccurate speedometer !?

[NoReverseYukon]

I bought an instrument cluster with the trans temp gauge to put into my 1500 series Yukon and the speedometer reads approximately 10% fast through all speeds. I thought it would be as simple as doing a speedometer calibration but the T2W says it is not needed, so then I thought I would change the tire size to see if that would cause any changes. The stock size is 265/70/16 so I changed it to 285/75/16. The speedometer read the same 10% fast, so obviously that change does nothing with the cluster and I changed the size back to original.

Next, I though maybe the needle is not in it's correct position on the air-core stepper motor. This not being the same type as the later-type steppers, I don't even know to determine where the correct position is.
So, I did a gauge sweep. Even though my speedometer is 120 MPH, the needle only went up to 55 MPH. Well that sucks ! I was expecting it to travel up to and over 60 MPH - that would explain the reading being faster than the GPS read.

For those who might have messed around with these speedometers, a few questions :

1) Will changing tire size then trying a speedometer calibration yield better results?

2) Is the T2W even capable of correcting an inaccurate speedometer?

3) Should the gauge sweep test have the needle stop at 55, instead of 60 even with a 120 MPH dial?

4) What has me even more stumped is that I actually have 2 clusters with the trans temp gauge - the one installed now is reading fast while the other one reads slow. This leads me to believe that somewhere in that BIN file is a value that can be adjusted to calibrate them. Which means that they can be calibrated - but maybe not with the T2W.


The local GMC/Chevy dealer says he can do this, in addition to adjusting the odometer. if I can, though, I would like to solve both of these problems myself.

Thanks for any and all help that is offered.

 

[NoReverseYukon]

@dougamiller
@doubeleive
Can either of you shed some light on this ?

Thanks.

 

[Tonyrodz]

If I'm not mistaken the needles should sweep all the way, not just 1/2 way. When I took my cluster apart, I swept the needles all the way to the right until it hits the internal stop then back to the right, lined up with the "0" not h--1st notch. All by hand.

 

[Doubeleive]

should sweep all the way and no the tech2 does not have the option too calibrate the speedometer, sounds like a stepper motor issue in both cases, unless maybe it came out of a 2500 or something that was programmed with a different gear ratio, has your pinion been changed?

 

[camaroz1985]

IIRC the Tech2/T2W tire size input is used for ABS calibration. I ended up buying a used Hypertech programmer for my Suburban just to correct the speedo.

Does sound like you have a bad stepper.

 

[NoReverseYukon]

I guess it's time to dig out my bench-testing stuff and test all my clusters again.

should sweep all the way and no the tech2 does not have the option too calibrate the speedometer, sounds like a stepper motor issue in both cases, unless maybe it came out of a 2500 or something that was programmed with a different gear ratio, has your pinion been changed?

Having a cluster from a truck with a different gear ratio was my thought as well, seeing as how the needle is off the same 10% through all speeds. I asked @DougAMiller if he knew if the axle ratio was stored somewhere in the IC BIN file, but he hasn't found it yet, if it is.

IIRC the Tech2/T2W tire size input is used for ABS calibration. I ended up buying a used Hypertech programmer for my Suburban just to correct the speedo.

Does sound like you have a bad stepper.

I have a box full of extra steppers. I'll find one that works.

Thanks all.

 

[DougAMiller]

should sweep all the way and no the tech2 does not have the option too calibrate the speedometer, sounds like a stepper motor issue in both cases, unless maybe it came out of a 2500 or something that was programmed with a different gear ratio, has your pinion been changed?

X2