Speedometer Suggestions

pmannfury · Post by **pmannfury** » Thu Oct 11, 2012 8:22 pm

Finally finished the engine rebuild but ran into a problem the first time I took the bike out. The speedometer seems to work fine until I reach about 40 mph and then it quickly jumps up to and moves between 70 and 80. I don't know if the speed is exact between 0 and 40 mph but it seems to track correctly. I've checked the cable and everything seems alright. Does anyone have any suggestions what the problem may be?

ByTheLake · Post by **ByTheLake** » Fri Oct 12, 2012 3:11 am

Are you sure you weren't actually going between 70 and 80?

Assuming your cable is nicely lubricated and not winding up and releasing, causing the jumping you're seeing, let's think about the 'insides'.

These speedometers are the typical "eddy current" type, where the cable spins a magnet inside a "speed cup" which is connected to the gauge needle. Here's an explanation of how eddy current speedometers work. In a nutshell, the faster the spinning magnet spins, the stronger the eddy currents are, which further turns the speed cup against its weak spring.

I know when I opened my CA95 speedometer, it was a mess. Lots of grit everywhere, and the original grease on the gears was missing or hard. With an earlier restoration, I encountered issues similar to yours , in addition to repeatedly snapped speedometer cables. For the past 3 projects, I've opened, cleaned and re-lubed the speedo, and each one has worked perfectly, although I completely understand how undesirable that task can be. Here's a picture of my CA95 speedo:

If the needle is jumping, that means the speed cup is jumping, too. I can see these possible causes:

1) Old grease not allowing the magnetic cup to spin freely, causing it to wind the cable until the tension is great enough for it to break free, causing the jump in the reading.

2) The cable is not lubricated sufficiently, causing it to wind up until it breaks free, causing the jump in the reading.

These speedos are no fun to open up, a process that consists of slowly bending up the crimped metal bezel and repeatedly stabbing yourself in the hand with whatever device was improvised for the purpose. If you decide to open it up, there are some good tutorials on-line, with tips on how to un-bend the crimp without creasing or damaging it. Otherwise, NoS speedos are available, too, but a 50 year old speedo could have hardened grease, too.

Larzfromarz · Post by **Larzfromarz** » Fri Oct 12, 2012 4:57 am

Nice explanation BTL very useful.
I experienced something similar on CD175 with a similar front hub. If you've had the front wheel off you might check the engagement of the drive to the hub. I've had this area become "loose" and the drive dogs would slip. Admittedly this seemed to occur at most any speed though. Still something to check if you've had it apart.

tjejenskille · Post by **tjejenskille** » Sun Jun 23, 2013 6:14 pm

I've noticed a similar issue with my speedometer on my CA95. I took apart my speedo, cleaned it up and lubed it. Then the original cable snapped, so I ordered a new speedo cable. It doesn't bounce around like it used to, but even with the new cable, it won't read my speed correctly. On a 55 mph road, it reads I'm going 55-60 mph but vehicles are passing me like crazy and I'm pretty sure they aren't all speeding. I've debated the drive gear on the hub being an issue, since I have a new cable and greased the speedometer itself. Who knows though huh, I just guess that my speedometer is reading about 10-15 mph higher than it should.

Larzfromarz · Post by **Larzfromarz** » Mon Jun 24, 2013 6:40 am

For me at 60 mph I'm less worried about the accuracy of the speedo than keeping it straight, and the buzz of the 160 may have something to do with it as well. it does sound like the speed cup is still dragging a bit.
Borrow a pocket gps and you'll know for sure how close you are.

ThunderMcAwesum · Post by **ThunderMcAwesum** » Tue Jul 02, 2013 2:51 pm

Can anyone tell me how to correctly open a speedo up? I managed to get mine open by prying the chrome bezel but managed to crack the metal in a couple places and mar the chrome in general.

Larzfromarz · Post by **Larzfromarz** » Tue Jul 02, 2013 4:30 pm

You have the correct idea, you just have to be careful about it. Crimping it back down can be even more fun...

ByTheLake · Post by **ByTheLake** » Tue Jul 02, 2013 7:32 pm

If you're tearing the bezel metal, then you're un-crimping it too quickly. Make several passes around the bezel, lifting it just a bit with each pass. The more time you take with this, the better the results will be. Same thing when re-crimping it ... a little with each pass.

A layer of electrical tape around whatever tool you're using can help avoid damaging the bezel metal, too.

tjejenskille · Post by **tjejenskille** » Sun Oct 06, 2013 8:14 pm

I discovered my problem with incorrect speedo readings. Very simple, with the new speedo cable, I failed to tighten the screw-on portion at the wheel hub on the drive gear all the way. I took a pair of pliers since it was a tight threading, and cinched it on all the way and now I can read how fast I'm going!

Benly Gamecock · Post by **Benly Gamecock** » Sat Jan 31, 2015 4:16 pm

Just replaced my speedo with a used one from Ebay, it is reversed and when going forward, the needle buries to the left? I don't see anyway to reverse it?

ByTheLake · Post by **ByTheLake** » Sat Jan 31, 2015 5:27 pm

Benly Gamecock wrote:Just replaced my speedo with a used one from Ebay, it is reversed and when going forward, the needle buries to the left? I don't see anyway to reverse it?

Did you have a working speedometer at some point earlier?

If the needle is going the wrong direction, that suggests that the cable is spinning in the wrong direction. The only way I can envision this happening is if the speedometer drive unit was on the opposite side of the wheel. Is the drive unit on the right side, like in the picture below?

I'm not aware if there were variations of the speedo drive throughout the Benly's existence - perhaps Sam or Chip would know. Otherwise, post a few pictures of the speedometer and the drive unit - that might help.

Cheers.

Benly Gamecock · Post by **Benly Gamecock** » Sat Jan 31, 2015 8:41 pm

The bike didn't have an installed speedo when I got it, just one in parts.
I installed it as you have pictured as the wheel connector was on the bike.
I have no clue how to get it to turn in the opposite direction.

Spokes · Post by **Spokes** » Sun Feb 01, 2015 3:49 pm

My guess is the speedometer is heavily corroded and not turning backwards. I've dissected several speedometers to find out what makes them "wacky". Every time the answer was rust. I once de rusted a really bad speedometer only to have the speed reading at 70mph....at maybe 5mph.

All I can suggest is to try another speedometer..

Benly Gamecock · Post by **Benly Gamecock** » Sun Feb 01, 2015 5:52 pm

I figured it out, the cable was binding I think because it is too long, I managed to straighten it out enough to get it to work correctly.
Now I just need to get the oil burning thing corrected
THanks

Benly Gamecock · Post by **Benly Gamecock** » Sun Feb 01, 2015 5:58 pm

also, this Benly I purchased from "Erik S" last fall, he used to be on this forum

Four Wheel Forum

Speedometer Suggestions

Speedometer Suggestions

Speedo backwards