Broken TachometerBroken TachometerThe tach unit in my speedo broke a while back. I took it to a guy recommended by Charlie's in SF. He fixed it for a while, but it went back to freaking out and spinning like crazy. Then he fixed it again, but to no avail. He very nicely offered to refund the cost of the repair and told me I'd be best off finding a parts speedo or a new tach unit for the speedo and installing that into the one I have. Does anyone have the tachometer unit that fits inside the speedo, or a part speedo they're looking to sell?
How would you know for certain? The symptoms are..... tach meter would work well with mild driving around town until you hit 8k rpms regularly, on longer distance, faster, high performance riding, then the tach needle would start to go insane. You'd get to 8k rpms, and it would jump up to 11 instantly and then go way beyond (obviously broken), and when you returned to idle, it would go back to 1-1.5k (idle speed), but since it already snapped, when you hit 3k it would start to spin round and round. I've just disconnected it. I suppose I could buy the proper drill bit to test, but really I think it's busted.
Cable is def not dry. When I started having this problem, before I paid someone to try and fix it, I lubed the cable, to make sure it wasn't something simple like that.
Hi,
Check inner cable for clearance, when getting older over time the inner cable will stretch a bit. When the cable is getting warm (longer distances), the inner cable WILL expand a bit. When there is no room any more, the inner cable WILL push the clearance in the the tiny bearing and destroy it over time. No lubrication will prevent that. I suggest to loosen the outer cable a mm (at the tacho), tape it so that is keeps in place, ride a longer distance. and see what's going on. When this is the case, shorten the cable a mm, Many good tacho's are destroyed this way, hahahahah, Jensen assembly of Japanese motorcycles requires great peace of mind (Pirsig)
Tach Freaking outAK,
That bike of yours is being pretty cantankerous. Now the tach, too? Hmmmm. I recently took apart a couple of Dream speedo's to figure out how they work. I was shocked at how simple the mechanism is. As I understand it, your tach works the same way. The cable drives a cup with a magnet in it (on a speedo this drives gears that work the odometer). A smaller cup fits into the top of the magnet cup and the spinning magnet tries to move the smaller cup. The smaller cup is attached to the same shaft that the speedo needle is attached to. There is a bushing under the speedo needle and at the bottom end of that top shaft is a clock-type bearing (pointed needle?) that isolates the speedo needle shaft from the magnet cup shaft. This allows the speedo needle to "swing" relative to the speedo cable. The speedo needle shaft also has a clock spring attached to it. The principle by which the whole mechanism works is a spinning magnet working against the clock spring. The faster the magnet spins, the more it pulls against the smaller cup inside it -and the clock spring - and the tach/speedo needle swings to a higher number on the dial face. If the clock-type bearing is not sufficiently lubricated (or not smooth), the needle would swing alot higher than it should because of the added friction - against which the clock spring would have no chance. The problem is that it is difficult to take the needle shaft out of the unit without bending the clock spring (good thing I learned on a parts speedo, because I did learn the hard way). Without taking that shaft out, I don't know how you would lubricate that clock-type bearing because it is under the small cup that fits inside the magnet cup. You should ask the guy that rebuilt your tach if he lubricated that center bearing. If not, that could be the culprit. If it is, I suggect you try to fix it yourself. If you are careful, I think you could get it done. Your tach repair guy has already determined it is no good in its current condition. You can't really hurt it. My 2 cents.
Last edited by conbs on Wed Apr 25, 2012 3:14 pm, edited 1 time in total.
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