Speedo problems... Help!!

[kodiak]

so i picked up a mini speedo and tach from a company i wont name(dont wanna give them a bad name). here's the issue....
after 20 miles, the zero position moved. sitting still the bike said i was moving 50mph.
company wont return gauges, so bit the bullet and ordered a new one since i had the matching tach. got about 1500 miles, on it, and while cruising at around 70 today it suddenly jumps to the pinned position and stays there..... comes back down if i roll the bike backwards, but jumps right back to pinned when i start going forward. is there something on my bike that can be causing this issue, or have i just ended up with 2 junk speedos? (2nd one has always been off by about 10mph)
Bike is a 1980 CB750k
this was the first one...

 

[Big R]

Have you tried pulling the cable at the wheel (or the speedo)? The needle should drop down on it's own regardless, so I think it's a faulty unit......

 

[kodiak]

i did pull it on the first one that went bad, and it stayed at 50mph. the 2nd one just happened on my way into work and i haven't had a chance yet. break-time soon, so I'll be doing it then...

 

[Big R]

Now that I think about it, there was a guy on another forum with the same speedo with a similar problem - his locked up at 0 MPH though. Maybe it's a quality control issue from the manufacturer?

 

[kodiak]

unplugged the cable and nothing happened. hooked it back up. roll it backwards it goes down, roll it forwards it shoots back up...
I'm not even sure who the manufacturer is. it came from the distributor in plain box with nothing but a wiring diagram.... All i know is at $70 a pop plus shipping i cant afford to keep replacing gauges every couple months...

 

[Big R]

Sorry Kodiak, I don't know what else to tell you. I tried taking one of those speedos apart before, and it really wasn't possible without destroying it.

 

[kodiak]

thanks big rich...
I'll just hafta call the place in the morning. i've had really good luck with everything else i've gotten thru them so hopefully this won't tarnish my view of the company.

 

[hillsy]

Speedos work via a magnetic connection between the cable and the needle wheels, so there must be some debris inside the casing that is "locking" together the needle wheel and the cable wheel (might be some debris from the warning light wiring??)

But in other words - a faulty speedo and more than likely a quality control problem at the factory.

 

[kodiak]

Speedos work via a magnetic connection between the cable and the needle wheels, so there must be some debris inside the casing that is "locking" together the needle wheel and the cable wheel (might be some debris from the warning light wiring??)

But in other words - a faulty speedo and more than likely a quality control problem at the factory.

ok... that does make some sense. the other thing i just remembered is the needle started bouncing around like crazy for a minute or so before it totally went. jumping back and forth from around 80 to 120

 

[kodiak]

k... i feel like a dumb ass now...
talked to Herm over at DCC. Turns out the problem isnt the bike, or the gage. Its me. Wasn't smart enough to isolate the gage from the vibration. never even crossed my mind even tho i knew better. so now that i've wrecked 2 perfectly good speedos, i've gotta run to the hardware store and get some rubber washers before i mount the 3rd one.
Hopefully everyone can learn a lesson from my mistakes!