No speedometer until installing driveshaft.

seedcleaner · Nov 29, 2022

Working on an auto 1997 k3500. After installing 2000 7.4l engine, and rebuilt tranny with a 1996 engine harness, I didn't have speedometer working. I assumed it was a wiring issue from the new 7.4 and 1996 wiring. I would put the truck in gear, with no rear driveshaft, and the speedo didn't register.

I put that issue on the back burner to focus on other things. In doing so, I finished some items and installed driveshaft to take it for a spin. Speedo works now. Is it possible the speedo is getting a reading now from wheel sensors instead of the transfer case? I could try to confirm all of this by removing driveshaft and seeing if speedo quits again, but asking here would be easier!

Thanks!

Erik the Awful · Nov 29, 2022

Your wheels turn whether or not the driveshaft turns them. Or were you referring to running it with the wheels off the ground?

Schurkey · Nov 29, 2022

The transfer case output shaft is probably located by some bearing in front, and the driveshaft spinning in the tailshaft bushing. Keeps the shaft centered between the two supports. The reluctor for the vehicle speed sensor rides on, and spins with the output shaft.

No driveshaft--the output shaft isn't supported at the rear, the shaft and it's reluctor drops far enough away from the sensor that the sensor signal is too weak for the computer to read. When the driveshaft yoke is in place...the reluctor is positioned properly and the sensor generates a readable signal.

Or am I wrong? I haven't been into a transfer case in ages.

No speedometer until installing driveshaft.

seedcleaner

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Erik the Awful

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Schurkey

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