spedo calibration

Shav0 · September 17, 2006

I recently put 33's on my 89 GMC and now the speedometer is off about 15km/h. I noticed its a reluctor wheel/pulse sensor and not a cable. Is there anyway to re-calibrate, maybe through the ECM?

Also, I've been chasing a noise inside my cab with no luck. Whenever I turn the key either on, or off I can hear a loud buzzing noise for about 10 seconds then it stops. At first I thought it was a power antenna, but there isn't one to be found. A couple of my co-workers have the same year truck, and theres do it too, so im assuming it's somthing from the factory. It's coming from under the dash on the passenger side.

GM-Tech · September 17, 2006

I believe in '89 they were still using this little clip on the back of the cluster that had 8 legs. It'd plug into the cluster, which had 8 little fused holes. At the factory, they'd pop the appropriate fuses to calibrate the speedo.

In the field, we'd have to pop all 8 fuses, then break off the appropriate pins to accomplish the same thing.

You can still buy this kit, which consists of a harness to pop the fuses and a couple new clips. I don't think it comes with a chart to tell you what pins to break off based on tire size, but it's been a very long time since I did one of these so I could be wrong.

If MS3DALE see's this post, he can probably get you the part number. It's likely that if you just walk into a parts dept. and ask for this, you'll probably get a blank stare unless the parts guy is an old timer.

Your noise is probably an A/C actuator homing the door.

MS3DALE · September 17, 2006

Yep,I remember that setup,I might have to call our AC-Delco repair center but I should be able to get the part number for it,They used it from '88 to '91,Then after that they went to a vehicle speed sensor buffer,or "VSSB" (That was a module that was programmed with your tire size and axle ratio to calibrate your speedometer)

Shav0 · September 17, 2006

thanks for the help.

What exactly do you mean about the AC homing the door? My AC is removed, so if I can somehow stop this sound it would be great.

thanks again

shav

MS3DALE · September 18, 2006

I got the part number you need....25085515

Its refered to as..."Calibrator,Vehicle Speed Sensor-Unit For Speedo.Reprogram"

It list for $64.02 and is actually discontinued from GM,However there is still some available from GM that can be ordered,They only have stock available at three PDC's....Reno,NV.,Boston,MA. and Los Angeles,CA.,So depending on where your at it may take a few days to get.

There was also quite a few dealers across the country that had it in stock on the locator.

Hope this helps!