I bought a new Bell 8 function bike computer a few years back. I had intended to install in on my (then) 2007 Royal Enfield 500 Bullet motorcycle, which had an unreliable speedo/odo on it. I never installed it and sold the motor cycle. Then moved. So I decided to install it on my mountain bike. Opened the package and installed per the instructions. Sensor goes on LEFT fork leg, install magnet to within 1/32", etc. It turns on and I can set the wheel size, set for mph or kph, set the time etc. Go on a ride and won't read miles per hour. Came back and tried spinning the wheel both ways....nothing. Set the sensor closer to the magnet....nothing. Any way to bench test one of these things?
Thanks, Jon

i have 2 different bell comps.. not sure which one you have. on both of mine you can scroll thru them to get the info you want on the screen. i believe the button on right side does this. have you tried this?

If this is a wireless unit, make sure your sensor batteries are fresh and properly installed. If it is a wired unit, make sure the wires are undamaged and properly attached. Since the unit is a few years old, it is possible that you have oxidized contacts somewhere that just need a little cleaning. I have two Bontrager W4 wireless computers and on one of them the fork sensor has gone bad twice. LBS replaced free of charge both times.

Well, mine is just called the Bell 8 function. It may have been discontinued. After going through the setup stage, it goes to the screen that shows mile per hour and time. But when I rode it or spinned the front wheel (spinning in both directions) the mph area shows "0". The batteries, while old, are not dead. It goes through the setup process just fine and shows 0 mph and time. When I couldn't get it to read the speed I removed everything. The clamp to strap the pickup to the fork leg is pretty pathetic. Like a plastic hose clamp.
Also, it is a wired unit, not wireless.

Pop the head off the mount and make sure all the contacts are clean. Make sure the magnet is passing where it is supposed to (there is usually an arrow or line on the pick up showing where the magnet needs to pass) and get it really close (like almost touching) and see if it picks it up. Changing the battery would be the next step.

And the unit doesn't care which way the wheel travels or which fork leg it is mounted on. Every time the magnet passes it momentarily closes a contact.

Most common problem is the magnet doesnt pass close enough to the sensor. Take off the magnet and pass it by hand near the sensor to make sure it really does work. You should see something other than zero. Sometimes it takes a few tweaks to get the computers setup just right.

-SP

Even though the battery has enough juice to run through the various screens, it may not be enough to register speed etc. If you cannot get a reading even with the magnet and sensor in your hands, try replacing the battery.

I have an old Trek 1995 wired cycle computer that had a similar problem. Since my unit is old (and a wired one at that), what I did may or may not apply to yours, but this is how I diagnosed:

Figured either the unit wasn't getting enough of a signal from the sensor OR maybe the battery was going bad. Since the LCD screen display looked nice and black and the buttons all worked, I suspected the sensor at first.

Adjusted sensor to be withing 1mm of the magnet. No change.

Tried a stronger magnet I had: waved it by hand in front of the sensor. No change.

Took the computer off out of the slot on the handlebars and hooked up my multimeter to the contacts in the shoe that the computer normally attaches to. Tested the resistance as the magnet went by. Each time it passed, the resistance went to zero. Good.

(The sensor must thus be a little magnetic proximity switch, and the computer simply interprets the number of times the circuit closes through those two contacts. Very simple, effective process.)

At this point I was satisfied that the computer wasn't operating correctly since the sensor operated just fine with my multimeter. I replaced the battery in the computer last week and it has been working great so far.

I suspect you could test the computer as well just by using a small length of wire and make periodic contact between the two terminals that go to the sensor. The computer should simply count each contact as a revolution of the wheel. So you can hand-simulate the process and you should get a reading.

good trouble shooting

Some real good information here. I have all parts removed from the bike now. I did try to hold and move the magnet and sensor together with the unit turned on and there was no change at the computer no matter how close I put these units. Also, the computer info sheet says it has an automatic turn off if it sits for a few minutes. Then, if you ride off the sensor/magnet, as the wheel turns, will turn the unit back on. I sat there with the parts till it turned off, and again moved the sensor and magnet by each other and it did not turn the unit on as it is supposed to. I think I'll get a new battery and try this again as suggested here.
Thanks. I'll let you know how it turns out.

Jon

Did the new battery fix it?

I live near Hilo on the Big Island of Hawaii. I tried to find the battery (T1142/AG12/etc). Tried Wal Mart, Target, Office Max and noone had an equivalent battery. So I ordered it from Amazon.com. I'll have to wait a week or so.
Thanks for asking. Some things can be hard to find here.

Jon

the battery can also be found at your local Radio Shack store .

Got the battery from amazon and installed it. It perked up the snappiness of the functions maybe. But, still no reaction from either spinning the wheel with everything installed. Tried holding the sensor in my hand and using other magnets with zero results. This unit is probably 3-4 years old but was still in the original package and unopened. I doubt Bell would do anything due to the age of this unit.
Dam. I really only wanted to be able to read miles per hour, total miles, and to have a resettable tripmeter.

have you try moving the magnet closer to the sensor ? there should be only a few mm apart .

Yeah, I've tried varying the distance from almost zero clearance etc. Someone said the gauge should react even if the parts are in my hand moving them together. I get nothing. I'm wondering if the sensor is bad. Though the kit was unused and in the original packaging till about two weeks ago, it's way beyond any warranty time frame.

there could be a break in the wire somewhere ,which you can track down with a ohm meter (multi tester) or there a problem with the switch . the part you pass the magnet . here check this out ,https://sheldonbrown.com/cyclecomputer-troubleshoot.html , I hope this help .