Attempting Speedometer Repairs, Need some advice |
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Attempting Speedometer Repairs, Need some advice |
ericread |
May 7 2010, 08:19 AM
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#1
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The Viper Blue 914 Group: Members Posts: 2,177 Joined: 7-December 07 From: Irvine, CA (The OC) Member No.: 8,432 Region Association: Southern California |
For the past month, whenever I go above about 35 MPH, my speedometer begins to whine and the needle jumps around to a very high speed, far in excess of the speed I am traveling.
I first disassembled my speedometer. There are basically two parts. The part on the left connects the speedo with the cable, and causes a magnetic disc to spin. The part on the right has the speedometer dial and includes a metal ring of which the magnet spins inside. My understanding is that the magnet and the metal ring should never touch. The magnetic field from the magnet causes the ring to be advanced, which in turn causes the dial to advance. Here we see the magnetic disc that spins from direct connection to the speedometer cable. To the left of the speedometer dial, we can see the outside of the metal ring the magnet spins inside. This is a picture of the metal ring. Upon closer inspection, you can see some scoring on the upper right side of the inside ring. It appears that the spinning magnet is rubbing against the metal ring, which would explain the issues I have been experiencing. If I understand the theory of operation correctly, there should be no metal to metal contact here. There are a two adjusting screws on the back of the magnet assembly. The flathead screw would seemingly adjust the magnet forward and back. Which direction should I go??? And the second adjustment is a very small screw with a retaining nut near the center of the moveable assembly. Will adjusting this screw move the magnet closer/farther from the metal ring? And what effect would this have on the speedometer reading? Any thoughts? |
charliew |
May 8 2010, 04:54 PM
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#2
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Advanced Member Group: Members Posts: 2,363 Joined: 31-July 07 From: Crawford, TX. Member No.: 7,958 |
I agree one of the bushings has worn and the cup and the magnet are rubing a very small amount. A jack leg repair (thats a old ncr term for guys with silver solder repairing cash registers without good parts) might be to grind a small amount off the magnet to reduce the od. And then put a little clock oil on the shaft and bushing. The next thing that will go wrong is the drive gear will loose it's mesh with the driven gear and the odometer will quit working. Really speedos are pretty cheap. Just keep the old one for posterity if you want to keep up with actual mileage. You might also file the alignment holes a little and shift the cup to center it better to give a little more room if it is just off centered more one way than the other.
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