Rabbit speedo misbehaving

[ldeikis]

I apologize if this is inappropriately off-topic (asking about the speedo instead of the motor) but the kids on the 'tex had nothing useful to offer and I don't know where else to look:

My 81 rabbit has developed this speedometer issue where the needle swings erratically upwards about 15mph or so.  It's accompanied by a light vibrating sound coming from the cluster--sounds a LOT like radio static, actually, which made me wonder about if there's any electromagnetrical trickery in there that could be wacking out?  It's intermittent--it first happened almost 5000 miles ago, then went away for a good 1500, then became more and more prevalent.  It'll sit rock steady at the correct speed, then out of nowhere the vibratey noise appears and the needle bounces around all over.  It seems to bounce higher, ie if I'm driving 65 it bounces between 65 and 75 or 80 and back and up and back and up.  Then it'll stop bouncing.  Then it'll start.  Sometimes I'll drive 200 miles without it ever happening, sometimes I'll drive 100 miles and it'll hardly stop.  Seems unrelated to speed, temperature, rain, or the use of lights/radio.  Over the last month it's gotten a ton worse, so I can hardly get to the store without it misbehaving.

The kids on Vortex said the cable was binding and I needed to lube it.  I pulled it out and it felt totally smooth, but I used a gizmo for injecting lube around motorcycle cables to push some cable lube in there anyway, and it seemed to have no effect one way or the other.  The odometer doesn't appear to be affected that I can tell.  I've had the car for about 40k miles and aside from reading a hair low due to the wrong plastic gear in the trans-end of the cable, I haven't had any irregular gauge issues besides occassionally not clicking over the tenths for a moment.

Hope someone here can help...  I kind of didn't want to waste this community's time on it, but I expect someone here knows where to look.

Thanks,

Luke in NY

[rabbitman]

My personal conclusion is that the part that spins inside the speedo itself is worn or dry.

These work by a magnetic wheel spinning inside a "cup" shaped wheel and the faster the magnet part spins the higher the needle reads, there's a tiny little copper "lawn mower" type recoil spring that tries to hold the needle at 0mph.

I haven't found a way to get the magnet wheel/bushing assembly apart to lube it, oil will quiet it down but centrifugal force will fling it out and it'll bridge the gap between the magnet wheel and "cup" wheel and cause the speedo to read progressively too high the faster you go.

You can get it apart and at least wash stuff out but it's hard to make it still be accurate when it goes back together.

[Rabbit79]

I had the exact same problem with mine except it wasn't making any noise. The wheel turned easily by hand so I don't think lubrication was an issue. The only thing I could figure was that over time that magnetic wheel had lost some of it's attractive force. I finally just sent it into a speedo shop.

[GEE-BEE]

Too bad it's not a 1980 ( round ) I have a extra with 4900 miles on it

GB

[Rabbit79]

You know the more I think about this problem, the more I wonder if it's that little spring that causes this to happen. Mine did the 'flop around' thing for a long time and eventually it got so bad that as soon as I got going over about 5 mph it would just flop all the way to the max speed peg. 5 to 130 in half a second. That's some serious power. As that outer cup wheel is driven faster by the speedometer cable, it drags the inner wheel along behind it by magnetic force, and this inner wheel has to overcome the tension of that little return spring. It seems if that return spring were to start losing tension over time it might cause this kind of erratic behavior, and once it went really bad it would just flop all the way up to maximum as mine did.  Now that I think back on it I think that's the conclusion I came up with as opposed to my loss of magnetic force theory. (sorry it's been a few years since I had it apart). Either way though I've never seen one of those little springs for sale and I have no way to calibrate it so my only recourse was to buy another one or send it in.