probably the cheapest would be swapping out the gears in the transmission tailhousing.... but most labor intensive. adapter gearboxes exist but are several hundred bucks

 

although I have seem them, I have never done this. Inside the gauge cluster they have little potentiometers to calibrate stuff. If you took it off the circuit board and extended it with some wire, you could calibrate it while driving to a portable gps.

 

wow, that just blew my mind, never thought of that haha.
Very good method though, great idea.

 

I had mine off a few weeks ago and I looked inside and couldn't find anything visible i can adjust? It'd be nice to get it adjusted.
Now that I have the W58 from a SC300 and 3.41's in the rear (or was it 3.42?), the speedometer is WAY off.
50mph is 61mph actual. The faster I go the further it is off...

 

Yeah, only the tach is adjustable by potentiometer. To correct the speedo those of us with electronic speedos can use a yellow box

Official home page of the Yellow Box Speedo Recalibrator

 

Smartphone with max speed app. match your speedometer to what app says. Not 100% foolproof but gets you in the ballpark.

 

moonbeam, just downloaded that app. i'll have to check it out tomorrow. thanks for the heads up.

 

I used GPS Speedometer app a while back, the truck is reading 83.333% of true speed, roughly.

 

Thread bump. My 88 22R single cab 5 speed is ahead 10mph what my real speed is. Anyone have a fix?