I asked this in my build thread, but no one has responded, so I'm starting a new thread.

My speedometer doesn't work. It won't move the needle until I'm doing about 25 mph, and then it usually bounces. As I understand the way it works, the spinning magnet caused the needle "bowl" or "cup" to move. The faster the magnet spins, the higher the needle goes.

There is nothing in this speedometer that I can detect being magnetized. I touched a flattened staple to both sides of the magnet and also to the cup, but the staple was not attracted to anything in there. I think this is the problem. Since it doesn't start to move the needle until I'm moving about 25 mph, maybe the magnet is really weak? It is, after all, 63 years old.

How would I go about re-magnetizing it? Any ideas are welcome.

 

Locate a neodymium magnet. These are magnets made of neodymium, iron and boron. They can be bought in science supply shops or online.
Identify your old magnet's poles. All magnets have a north and south pole. Contrary to popular belief, these poles are usually located on the long, flat sides of the magnet, not on either end.
Determine the neodymium magnet's poles. Occasionally they will be marked. If not, find a compass. The side the needle points to will be the south pole of the magnet, because opposites attract.
Rub one pole of your neodymium magnet against the opposite pole of your old magnet. The sides that attract each other are the ones that can recharge each other. Repeat with the other side.
Good luck with it. I have a GPS activated speedo in mine so I have no cables at all just a small antenna on the dash.

 

I don't know how long anything would work, but in grade school we magnetized stuff with an electromagnet. Just windings around a bolt, hook up to a battery.

 

Try using a better looking staple.

 

ROTFL!!!!!!!!

 

Works great if you need a magnetised screwdriver, too. Half a dozen or so winds around the shank and quickly swipethe wire ends across your battery posts.

But since Joe is working with such a small magnet and in such a small place, I can not figure out a way to re energize his magnet. We're talking some mighty small and fragile parts here.

Missy Green has a working odometer but my plug in GPS indicates her speed quite accurately. These old speedometers were notoriously inaccurate when new. More of an indication that you are moving.

 

Joe, just in case you can't decide what to do with your tax refund, keep in mind that the 51-52 style speedo is available brand new a couple of places. They were used up to mid-60's in parcel vans and bread trucks. Also, you're pretty close to United Speedometer in SoCal, they can fix it for sure. (May be cheaper to buy new)

 

OK, after realizing that I was using an ugly staple to test magnetic attraction, I decided to use a really pretty refrigerator magnet to realign the magnetic flux core of my speedometer.

Ilya was right. That's all it needed.

I did actually use a magnet off the fridge. It was the strongest of the many found on a grandparents' refrigerator. I used the grade school technique of aligning the molecules by contacting the arm and sliding the magnet in only on direction. That effectively re-magnetized the speedo arm.

I then used the variable speed drill method of calibrating the device. I can't get this unit to calibrate correctly to record 1 mile in 1 minute at 60mph. There just isn't enough adjustment to the spring without binding the mechanism into the odometer.

But, I'm ok with that. The speedo registers after about 5 or 10 mph, and is going to be inaccurate until (if) I change the drive gear to a 20-tooth to match my tire size, which I may never do.

Now on to the next problem.... but that'll wait until after the Super Bowl.