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Thanks to this post by Jeff K, I was finally able to calibrate a couple of speedometers using my desktop computer, a length of wire, and an old speaker extension cable from the 99cent store. I am not recommending that anyone follow these procedures, since a wrong move could result in a fried computer, or at least a fried sound card. Just in case anyone wants to try, even after the disclaimer, here are the directions:
The first step is to download signal generation software. A version for windows can be found here . I didn't search Freshmeat.net for a Linux version since I didn't feel like compiling source code.
Next, procure a length of wire, and an old speaker or headset cable/wire.
The next step is to remove the speedometer from the instrument cluster.
Remove the cover from your computer. On my AT power supply, the yellow wires going to power drives are 12 volts positive. Find a connector that is not powering a drive, and make it accessible. Be sure to identify which connection in the connector is 12 volts positive.
Connect the wires to your speedometer. If you look at the bottom of the card on the back of the speedometer, on the side facing forward, the the labels for the connectors will be visible. The ground wire from the speaker cable goes to the - connection, the + wires from the speaker go to the signal connection, and the loose length of wire goes to the positive connection.
Put the connector for the speaker wire in the sound card's speaker output. Start the signal generator, and turn up all of the volume controls. To test the speedo, CAREFULLY touch the loose wire on the positive connecction to your computer's 12volt postive source. Depending upon which frequency is chosen, the speedometer should display a specific speed. Test the speedo at 44.44444 (should be 20mph,) 111.1111111 (should be 50mph) and 177.777777 (should be 80mph). Remember the error amounts.
Take off the speedometer face plate, carefully removing the needle. Remove the odometer assembly by removing the three phillips screws. Now you can see the workings of the speedometer. On the standard 85mph speedometer, 20mph is straight to the left, 80mph is straight to the right, and 50mph is straight up. Since the big weight is where the needle points, adjusting that will have little effect on the 50mph calibration. Since the little weights are above each other at 20 and 80mph, they have little effect on the calibration at those speeds.
There is a little tab near the upper right of the speedometer that determines where zero is. If all of your speeds are a specific amount high or low, this tab can be bent slightly to reset where zero is. For instance, if all speeds are about 3mph high, the needle can be repositioned at -3mph for zero, and the tab bent to bring it back to zero.
If the 20mph is low and the 80mph high, move the big weight inward. If 20mph is high and 80mph low, move the big weight outward.
With the big weight at the top of the speedometer, you can adjust the 50mph speed by shifting the little weights leftward if the speedometer reads too fast at 50mph, and rightward if it reads to slow at 50mph.
After adjusting, retest. I had to test about 4 or five times, re-installing the faceplate each time, then removing after the test. Did two speedometers in about an hour, not counting removing the cluster from the car.
Hope this helps someone.
The first step is to download signal generation software. A version for windows can be found here . I didn't search Freshmeat.net for a Linux version since I didn't feel like compiling source code.
Next, procure a length of wire, and an old speaker or headset cable/wire.
The next step is to remove the speedometer from the instrument cluster.
Remove the cover from your computer. On my AT power supply, the yellow wires going to power drives are 12 volts positive. Find a connector that is not powering a drive, and make it accessible. Be sure to identify which connection in the connector is 12 volts positive.
Connect the wires to your speedometer. If you look at the bottom of the card on the back of the speedometer, on the side facing forward, the the labels for the connectors will be visible. The ground wire from the speaker cable goes to the - connection, the + wires from the speaker go to the signal connection, and the loose length of wire goes to the positive connection.
Put the connector for the speaker wire in the sound card's speaker output. Start the signal generator, and turn up all of the volume controls. To test the speedo, CAREFULLY touch the loose wire on the positive connecction to your computer's 12volt postive source. Depending upon which frequency is chosen, the speedometer should display a specific speed. Test the speedo at 44.44444 (should be 20mph,) 111.1111111 (should be 50mph) and 177.777777 (should be 80mph). Remember the error amounts.
Take off the speedometer face plate, carefully removing the needle. Remove the odometer assembly by removing the three phillips screws. Now you can see the workings of the speedometer. On the standard 85mph speedometer, 20mph is straight to the left, 80mph is straight to the right, and 50mph is straight up. Since the big weight is where the needle points, adjusting that will have little effect on the 50mph calibration. Since the little weights are above each other at 20 and 80mph, they have little effect on the calibration at those speeds.
There is a little tab near the upper right of the speedometer that determines where zero is. If all of your speeds are a specific amount high or low, this tab can be bent slightly to reset where zero is. For instance, if all speeds are about 3mph high, the needle can be repositioned at -3mph for zero, and the tab bent to bring it back to zero.
If the 20mph is low and the 80mph high, move the big weight inward. If 20mph is high and 80mph low, move the big weight outward.
With the big weight at the top of the speedometer, you can adjust the 50mph speed by shifting the little weights leftward if the speedometer reads too fast at 50mph, and rightward if it reads to slow at 50mph.
After adjusting, retest. I had to test about 4 or five times, re-installing the faceplate each time, then removing after the test. Did two speedometers in about an hour, not counting removing the cluster from the car.
Hope this helps someone.
Mike Walsted - Sold my 1986 5-speed TurboCoupe