Swap to Canadian Cluster (in km/h and C degrees)

[mikez71]

They have different speedo scaling, I don't think they are mechanically anymore accurate than stock.
I'm guessing they just paid to have one tested and 'certified' with the proper tires etc.

 

[Marky Dissod]

They have different speedo scaling, I don't think they are mechanically anymore accurate than stock.
I'm guessing they just paid to have one tested and 'certified' with the proper tires etc.

Any time a large quantity of anything is made, quality will vary among both the raw components and the finished products.
It's pretty likely that the finished products whose test results are a cut above wind up 'Certified'.

 

[mikez71]

I feel you're giving the needle accuracy too much weight.
What would they test on the motor? If it spins to position faster, or if it's missing some steps?

Even more difficult to believe, is that GM would spend the money to do that.
I don't know, but I bet a stock speedo is every bit as accurate.

I'm guessing it was a requirement they needed to fulfill by testing, most likely 1 vehicle and 1 speedo.
Didn't vary by more than x%, now that speedo/tire combo is certified.

Found some info about stepper motors in speedos.. https://issautomotive.com/blogs/news/are-stepper-motors-accurate

 

[Marky Dissod]

... you're giving the needle accuracy too much weight.
What would they test on the motor? If it spins to position faster, or if it's missing some steps?

Even more difficult to believe, is that GM would spend the money to do that.
I don't know, but I bet a stock speedo is every bit as accurate.

I'm guessing it was a requirement they needed to fulfill by testing, most likely 1 vehicle and 1 speedo.
Didn't vary by more than x%, now that speedo/tire combo is certified.

Found this intro to speedos. https://issautomotive.com/blogs/news/are-stepper-motors-accurate

In the Caprice 9C1 days, every 9C1 speedo got tested/checked.
If it barely failed it went in a civilian Caprice because accuracy at illegal speeds was not as important.
I think the test was to supply a signal commensurate with 80MpH - 85MpH, the closest ones got 'Certified'.

 

[mikez71]

Interesting, I don't know anything about the 9C1, but it sounds like it maybe cable driven? And there maybe some calibrate-able electronics in there...
I suspect ours are different enough though..

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silicon212 01-31-2007, 12:25 AM

For any given speed at any given ratio, both speedos will display the same speed, while the 9C1 (U11) unit is capable of displaying more of it, at more precise measurements (the standard unit is calibrated in 5MPH chunks while the 9C1 is calibrated in 2MPH chunks).

The difference is in the heads themselves - the standard head is adjustable to a degree while the U11 unit is sealed (hence 'certified'). You have to take into consideration things such as final drive ratio, tire size etc., to actually get it to display the proper speed, as with any speedometer.

Most of the 9C1 certified units are certified with 3.08 or 3.42 ratios and P225/70R15 tire sizes - deviate from those and the speedo will no longer be 'certified', although they will display more than accurate enough for most people.

In short, if your car has a standard speedometer that is the same physical dimensions as the U11 unit, if the standard unit displays 55MPH, the U11 will also display 55MPH leaving everything else well enough alone.

 

[Marky Dissod]

Most of the 9C1 certified units are certified with 3.08 or 3.42 ratios and P225/70R15

Back in those days Caprices 9C1-L05 got 3.42 & 225/70HR15, followed by Caprices 9C1-LT1
which got 3.08 & either 225/70HR15 (SEO VZ2 limited to 130MpH) or 3.08 & 235/70VR15 (limited to 149MpH).

 

[GMCChevy]

The certified ones usually go up higher then the otherwise stock ones and when they're digital they read differently. Each is tested for accuracy and calibrated. The normal ones aren't.

 

[chutkin]

This discussion is getting interesting

Hi MikeZ71,

Does other gauges show correct values? Temperature, oil pressure, fuel?

Did you adjust mileage or this number came with the cluster?

Thanks,
Ivo

 

[mikez71]

Hi Ivo!

Mileage came with cluster.
No reprogramming needed, if incorrect mileage does not bother you.
All gauges looked perfectly normal.

 

[chutkin]

Hi guys,
I got the cluster, earlier then expected.
It looks brand new as it was described at ebay.
Unfortunately, I will not be able to install it soon because the tuck is on disassembled on jack stands.
I will keep you updated.
Cheers,
Ivo