120MPH Yukon Denali / Tahoe limited cluster swap issues

[97K1500Silverado]

Hi all. I have a 1997 k1500 ECSB. see YouTube link in my signature if you want to see videos of it.

I’ve purchased 2 Denali / Tahoe limited 120mph clusters and both are off on the rpm and Speedo. Rpm reads high, my scan tool and old cluster says 2k rpm while the new cluster reads 2.4 / 2.5k. Speedo on my original cluster is dead on but new clusters are only accurate until 25mph or so then are way off like reading 60 when I’m doing 75. Again my scan tool is accurate and my original cluster.

So in the end I popped off the needles for rpm and speedo, pushed the rpm when truck was at 2.5k on scan tool. Did same thing, scan tool read speed at 70mph and I put needle on at 70 mph.

Now only issues are the rpm reads low from idle to 1.5k but is accurate higher up in rpm like 2 - 3.5k is accurate but it reads a bit high at 4k - 5k my scan tools says 3.8k - 4.8k.

Speedo reads a bit low 10 when I’m doing 13-14 and 25 when I’m doing 27-28 but dead on 60 - 80mph or within 1-2 mph of gps.
Kind of odd both 120mph clusters act the same but my original cluster was correct all gauges.

If I try and set rpm correct at idle and speed correct at 10mph then they are both off higher in the gauge readings.

 

[HotWheelsBurban]

The speedo on Rawhide (97 C3500 CCLB, 5.7/4L80E/4.10 FF) seems to under read a little bit, like indicated 25 is actually 22 according to the speed checker machines and signs. My commute goes through West University Place, a landlocked suburb of Houston that has a 25 mph speed limit that they are pretty good at enforcing. The truck is set up for 245/75-16 tires and that's what it has on it. I haven't explored checking the actual speed with a GPS speedo app or anything, but I'd like to have an idea what could be causing this before our annual trip to Lone Star Roundup in Austin, in April.
Any ideas? Thanks, sorry for the slight thread jack.

 

[97K1500Silverado]

The speedo on Rawhide (97 C3500 CCLB, 5.7/4L80E/4.10 FF) seems to under read a little bit, like indicated 25 is actually 22 according to the speed checker machines and signs. My commute goes through West University Place, a landlocked suburb of Houston that has a 25 mph speed limit that they are pretty good at enforcing. The truck is set up for 245/75-16 tires and that's what it has on it. I haven't explored checking the actual speed with a GPS speedo app or anything, but I'd like to have an idea what could be causing this before our annual trip to Lone Star Roundup in Austin, in April.
Any ideas? Thanks, sorry for the slight thread jack.

Check with a gps speedo app on your phone. Even though your tires are the same size as what the truck door sticker calls for different tire brands are slightly different overall diameter. Aka they are all listed the same size but actual size is 31.6, 31.7, 31.8. Or your stepper motor is a bit off. Curious if it’s still off the same amount at 70mph or way off or accurate?

 

[fancyTBI]

They’re old, they’re off. They probably weren’t super accurate when new. You get used to it. Mines off in my ‘92 and in my ‘95. Oh well.

 

[HotWheelsBurban]

Check with a gps speedo app on your phone. Even though your tires are the same size as what the truck door sticker calls for different tire brands are slightly different overall diameter. Aka they are all listed the same size but actual size is 31.6, 31.7, 31.8. Or your stepper motor is a bit off. Curious if it’s still off the same amount at 70mph or way off or accurate?

Have to get an app, then find a place to safely get that fast, with no traffic around....
I guess it's not really a big deal.

 

[97K1500Silverado]

FYI I put my speedo needle on at 70mph not while driving but in driveway with rear wheels off the ground. Put trans in 3. Watched my scan tool until I was at 70 and put the needle on at 70. redid rpm in Park and held it at 2k on scan tool then pinned on needle. The other 4 gauges are correct across all clusters.