When working on the instrument cluster on my 65 200 6 cylinder, I had disconnected the speedometer/odometer cable. After I reattached the cable the speedometer needle began bouncing around while I drove, usually hovering around what appears to be the correct speed. I noticed that when I get to about 50mph though the needle seems to settle down. I have not had a chance yet to get back under the dash to remove and reattach the cable. Before I do it though I thought I'd ask what the likely cause of the bouncing would be. Is it possible to fit the cable back in incorrectly (and would that lead to bouncing)? Could I have somehow mangled something in the instrument cluster? Thanks.
Thanks for the responses. I went to an auto parts store and asked for a lube kit for the speedometer cable and gears in the dash and both guys there had no idea about any sort of kit. The one guy said I should use powdered graphite. Does this seem reasonable or is there something better?
Also, I'm still wondering why the bouncing needle problem occurs at lower speeds (say 35mph or less) but settles down around 50mph. Any explanation for that?
Finally, the guy at the auto parts store said that his guess was that the gears in the dash might be missing some teeth. How likely is that on the list of possibilities for causing the bouncing?
The last time I bought a speedo cable it came with the lube, It was kinda greasy and not dry powder.
The gears spin little magnets which in turn pulls on the needles magnet. The needle on a speedo is pulled to a certain point before the magnetic pull of the magnet is lost on it's rotation. If you're driving slowly there is more time before the magnet spins back around and pulls the needle again. That's the time that the needle tries to drop back to 0. The faster you go, the less time there is for the needle to drop and the farther the needle is pulled during each rotation. The lube is not just to lubricate the mechanism, but also to smooth out the reaction of the needle to the spinning magnet. That's why you need to lube the internal gears on the speedo; to add the *buffer* that the grease provides. It slows it down down by adding some very slight resistance to its movement. The faster you go, the less time there is for the needle to drop, thus the bouncing stops since there simply isn't time for the needle to drop before the magnet flies around again.
The other example I can use to explain it is...Have you ever watched the display on an audio parametric equalizer that has a delay built in to hold the peak levels for a split second before dropping back down? If another peak level comes along that's louder than the previous peak before the level has a chance to drop then it appears that the level is going up without having ever dropped, we know it did since we can hear it, but the visual display didn't have time to react and show you the visualization of the lower level. If you had two visual displays with one showing immediate frequency response curves with no delay and the other with a long delay, the one with immediate response would be like the unlubed cable, jumping all over the place and generally giving you a headache. The other would smooth out what your seeing by adding some buffering and keeping you from seeing everything, just the peaks as they happen. This is the lubed cable. This is the closest comparison I can think of to explain the spinning magnets.
Again, He sounds like a retard. Why would it only bounce at low speeds and work fine at high speeds? If there were missing teeth, then that would screw up your odometer, not the speedo. Plus if there was a direct drive of the speedo, then you'd be more likely to damage the speedo at high speed instead of actually having it work better! The damage caused to the remaining teeth just through sheer inertia of the gear coming around and slamming into the next tooth after the broken one...sheesh!
Well the grease approach worked great, thanks again!
I have another question (maybe I should start a new thread, but I'll try here first). The emergency brake handle has broken on me twice (65 6 cylinder). The first time I practically had to destroy the handle in order to get it off because I could not get the pin (or whatever it is called) out of the shaft. I put on a new handle and after about a year this one broke! I probably should learn to grab it closer to the central shaft rather than out on the edge.
In any case, I am having the same problem as before getting the handle off. Once I get the pin out this time though I am thinking I'd like to put on the new handle using some other approach such as drilling a hole so that instead of using the pin I might slide a small screw all the way through the shaft and put a nut and lock washer on the other end.
Does this sound reasonable? Is this difficulty with removing the emergency brake handle something that seems to happen a lot? If so, is there a typical solution to this problem? Thanks.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.