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Speedometer doesn't return to 0

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Tomblin

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I am finishing up a 7 year refurbishment of my BJ8. When I started the project, the Speedo needle would bounce around and often just drop to 0. I have replaced the angle gear and cable. The car is now running and the speedo works fine as long as I am hitting new highs. But the needle doesn't come down. So currently it keeps a record of the highest speed I've been at. I removed the cable from the speedo thinking that it might drop, but it stays put. I looks like the problem is in the speedo. Before I send it off to Nisonger, does anyone have an obvious solution like a drop of oil somewhere?

Bruce Tomblin
 
Welcome to the Forum, Bruce.

I'm not an expert, but I've put a lot of time and money into BJ8 speedos (I think I have two 'spares' I acquired for parts in the parts drawer). Speedos are remarkably simple in theory and design, but are akin to a mechanical watch in operation. The angle drive and cable turn a magnet, whose eddy currents cause a disk--to which the needle is attached--to turn at a reduced rate; sort of a first derivative to the angular speed of the cable (like velocity is the first derivative of acceleration). The tripmeter and odometer are operated by ratcheting mechanisms that are directly driven by a worm gear off the cable. They can cause other issues, like a periodically jumpy needle.

There are a couple of things I can think of that would cause your problem; the first is that the needle is dragging on the speedo face or its 'bearing' has worn; have you tried the old movie trick of tapping the glass when you have decelerated or stopped? If that causes the needle to move, then that's your problem (the needle is 'returned to zero' by a tiny, weak spiral watch spring). The second is something else sticking inside the speedo. I don't think lubrication--I recommend a silicone lubricant as they seem to attract less dust--will fix your particular problem. If it's not the needle dragging you have to open up the speedo; something that is not for the faint of heart, but if you do there is some info here: https://triumph.daveola.com/NOTES/Speedo_Repair.pdf

NOTE: The angle drive needs a washer: https://www.mossmotors.com/graphics/products/PDF/021-511.pdf



 
Thanks Bob. I did tap the face with no success. Also, I did make sure to install that washer on the angle drive. I suspect that it is something internal to the Speedo. I'll pull it and see if I can get it to drop without opening it. This maybe a job for Nisonger. They converted my Tach to run with a Pectronix dizzy and seem to know what they are doing.
 
Tomblin said:
Thanks Bob. I did tap the face with no success. Also, I did make sure to install that washer on the angle drive. I suspect that it is something internal to the Speedo. I'll pull it and see if I can get it to drop without opening it. This maybe a job for Nisonger. They converted my Tach to run with a Pectronix dizzy and seem to know what they are doing.
Click to expand...
They will send you instructionsto use for calibrating your speedometer before you send it to them. It was easy to do and my speedometer and GPS match each other.
 
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