Speedometer doubled actual speed

[AC439]

I already search and doesn't seem like there is an identical issue in this forum. My car's speedometer has exactly doubled the actual speed today. It just happen all of a sudden. Turn off the car and turn it back on doesn't clear the problem. There is no bouncing of the needle and the odometer/trip meter stay the same speed (i.e. they don't double the miles count). I know this is all mechanical - the autotranny spins the cable which inturn spins the speedometer. So if the odor/trip meter don't speed up but on the speedometer, is the problem in the speedometer? I think it's an integrated unit but is there a way that I change the speedometer but keeping the original odor/trip meter? Lastly, is the speedometer able to be taken apart and be fixed? Thanks.- AC

[AC439]

Ok...I have resolved the problem. Just want to type a few words to share it here.

My speedo needle was bouncing before and I traced to the speedo cable. I found a lot of dirt inside the cable so I yanked it out and passed transmittion fluid inside to flush out the dirt. Then I put everything back in place. It solved the bouncing needle problem.

With yesterday's problem, I checked the transmission end of the cable. It was good although the clip was a pain in the *something* to get it click. Then I yanked out the dash cluster and found oil (those I put to flush the dirt out of the cable) over the back of the speedo connection. Apparently there was excess oil drain from the cable and got into the speedo. I then took apart everything and sure found oil inside the speedo mechanism. So the pure magnetic coupling for the speed display became "magneto-fluid" coupling. Since fluid has higher viscosity, it transferred more of the spinning torque into the speedo mechanism and made the displayed speed much higher than actual speed. And it just happened to be exactly doubled.

I then sprayed the electronic cleaner into the magnetic coupler and let it drain until clear. The cleaner fluid then evaporated itself. Put everything back into the car and it resume normal operation.

For those who oil the cable instead of replacing it (I'm a student and I'm cheap), if you experience similar problem and both ends of the speedo cable are tight, then you need to check if there are excessive oil inside the speedo mechanism. A drop of oil goes into the magnetic coupling will definitely increase the displayed speed. I read some other posts that some speedo will jump from like 40 to 70mph for a while. That could possibly be caused by oil or something in the magnetic coupler. Since the cable will not spin faster by itself, therefore the only possibility is the magnetic coupler.

Thanks for reading.

- AC