Speedo / Tach / Gauges: Odo works, speedo not so much

[TheBiz]

Driving my new (to me) 63 GT Hawk home I had some speedo problems and the needle broke off. I bought a replacement speedo from eBay and a NOS cable from SI. The odometer seems to be working fine so I assume the cable connections are good. However the speedometer needle isn't working.

As I was driving on my own I couldn't keep a close eye on the gauges but when I did look down the needle wasn't moving with my speed but was above zero suggesting it had moved at some time. Over the course of a half hour drive I noted the speedometer "stuck" at 6mph, 20mph, 28mph, 42mph and 80mph when I turned it off. I don't think the numbers are significant other than the needle didn't seem to settle lower at any time -- always higher.

Any suggestions on things I can check myself or do I need to take the speedo to a professional?

[Chucks Stude]

Sounds like it needs disassembly and cleaning. Someone should be able to tell you who is the best. I could get it handled in Houston, but in the prosperous northland, not so much..........

[JoeHall]

A quick check to isolate the problem(s) would be to unscrew the cable from the back of the speedo, reach up and "flip" the speedo drive (give it a quick spin) at backside of the speedo. If the needle jumps up to 10-40 mph and quickly returns to zero each time you flip it, it may be OK. Leave the cable unhooked, and hanging down below the dash where you can reach it. Drive down a deserted road slowly and hold the cable in your hand while putting your thumb on the cable, to feel if it is spinning. It should spin steadily and you should not be able to stop it as long as the car is moving. If it does not spin, pull the cable out from that end and inspect. If it is OK, coat it with ATF and reinstall it. The next thing to check would be the pinion on the tranny, which is at the other end of the cable. Hope this helps.

[JoeHall]

A quick check to isolate the problem(s) would be to unscrew the cable from the back of the speedo, reach up and "flip" the speedo drive (give it a quick spin) at backside of the speedo. If the needle jumps up to 10-40 mph and quickly returns to zero each time you flip it, it may be OK. Leave the cable unhooked, and hanging down below the dash where you can reach it. Drive down a deserted road slowly and hold the cable in your hand while putting your thumb on the cable, to feel if it is spinning. It should spin steadily and you should not be able to stop it as long as the car is moving. If it does not spin, pull the cable out from that end and inspect. If it is OK, coat it with ATF and reinstall it. The next thing to check would be the pinion on the tranny, which is at the other end of the cable. Hope this helps.

If the speedo did not check out in step one, remove it and you will find a metal cap on top of the bushing the speedo drive passes thr from the rear; that cap has a tiny hole in it which leaks down to a "wick" that lubes the speedo drive. Clean the area, remove the cap with a pair of dikes (to save time), and soak a drop or two of thin oil (i.e. 3-In-1 Oil) at time into the wick, and rotate the shaft back and forth till it loosens up. Stop adding oil as soon as it begins to loosen up, or else it will seep down to the face of the speedo. Reinstall the speedo and it will likely be OK, unless the shaft bushing is trashed, in which case it will still work better, but rattle.
Joe H

[gordr]

If the odometer works, the cable is OK. What you describe sounds exactly like the tiny bushing supporting the needle shaft just behind the instrument face is badly gummed up, probably from incorrect lubricant being used.

The "back end" of the needle shaft is bushed against the rotating magnet assembly, and if that bushing were sticky, you see (and hear) the needle pegging out against the top end stop.

Remove the speedo, open it up, wash the gummy oil out with a suitable solvent, maybe WD 40, let it dry, and lube it with genuine clock oil, obtained from a clockmaker or clockmaker supply source. May as well lube the rear bearing while you have it apart.

Or send the entire instrument in to a specialist, if you feel timid about taking it apart.