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Discussion Starter · #1 ·
98 VT100 C3 with ~35k miles. Got it last year with ~21k miles, and have been enjoying ever since. Only real issue now is the speedometer.......started maybe 6 months ago. At first, I just noticed the needle "bouncing," down 15/20 mph (or sometimes down to zero), then right back up to speed. More recently, it's been somewhat consistent in that it will be fine for the first 5-10 miles of a ride, then drop to zero and stay there. Later in the day, next day, next week, whatever---same thing. If I stop for gas, at the store, something short (off and parked for < 1hr), it will work again for the duration of a ride. Illumination and odometer is still displayed (just not clocking).

I've checked the connections at the harness and in the headlamp assembly, nothing stands out. I've seen the signal tests, but didn't figure that would be able to tell me anything, being an intermittent issue.

Can the speed sensor itself go bad? Only thing I can think of. I could live without the speedometer, just hate that I'm not able to track the mileage for maintenance reasons.

Any suggestions would be much appreciated.
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Well,,, learn something every day, Parts diagram shows an electronic speedo and a speed sensor. Didn't know any had that in 98. Check the mounting and connections to the speed sensor would be the 1st thought.

 

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Discussion Starter · #3 ·
Yeah....#10 is the only thing left to check. I've re-seated it (thought maybe it wasn't picking up a signal from the shaft?), but not sure how to test it. Guess the only thing left to do is replace it.

Thanks for the input.
 

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I would go through and clean all the battery and ground connections. May simply be a loose ground wire somewhere... More common than one would think, but the ground path is every bit as important as the positive side.

Not even sure where the sensor mounts on that one. Could whatever triggers it have an issue? As for checking it, Might consult the shop manual, has to be a test for it. I'd think it's some kind of Hall Effect sensor, best tested with an oscilloscope I suspect, Thinking if it's in an area metal shavings or debris might collect, they could interfere. Or if the mouning bolt was simply loose? (it might ground through the mounting...) May be it's just bad and breaking down from heat? Don't rule out the wiring between it and the speedo or possibly the speedo itself.

I would go through and clean all the ground connections
 

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Discussion Starter · #5 ·
I'm gonna try all of that, for sure.

The sensor is under the left side engine cover, right beside where the clutch cable terminates. There has to be something on the drive shaft itself that triggers it, not much different than a wheel/ABS sensor on a car. Only had it off the one time to make sure it was seated properly., but didn't see anything then. The wires are fixed to the sensor, and run up behind the battery mount to a harness under the seat. All of those connections are solid.

The test procedure is to raise the rear tire and turn it, with voltmeter leads on the harness and/or connections in the headlamp assembly. With it working right off the bat (cold) or after a restart, I don't figure it would tell me anything except that I'm all good.

Electrical issues are brain-racking enough not to have to deal with the intermittent aspect, too.

Again, appreciate the input, definitely gave me some direction.
 

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That is what I would do, raise the bike and turn the rear wheel and with a meter set to AC voltage it just may show a small voltage.
Or even on resistance it may show some change as the signal changes with rotation.
You should try it when it is working, then again when it stops, so you know what it CAN do.

Electricity is invisible, so like "oldguy" said you need a meter, oscilloscope, test light, or something to watch what it is doing.
Then, try to catch it when those pesky electrons are playing games and not working as they should !!!
 

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Discussion Starter · #7 ·
I understand.

The tricky part is knowing when it should be working and when it isn't. When it goes out, I'm moving. So far, anytime I stop for a short time (kill the engine) and start back up, it will work again for the duration. Parked overnight, I get the same thing the next day Since it doesn't start working after just a stop (red light, stop sign), I feel like it might have something to do with the ignition circuit......maybe similar to what a stepper motor does with the gauges on my Trailblazer. Then again, that wouldn't explain the issue after a cold start.

I work with the guy that sold it to me. Kept it garaged the entire time he had it (17-18 years) and only put 10k miles on it the whole time. Said he never saw anything like that, which I believe since I didn't see it for the first 4-5 months.

Lots of stuff to think about/try, for sure.

Thanks, guys.
 

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Check the frame ground also.
Maybe a poor connection .
If it corrects itself each time when you cycle the key, it may be an internal meter problem.

But looking into manuals for your 1100 in that year range,I don't see the electronic speedo.
All that is shown is a cable operated unit.
 

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I would go through and clean all the battery and ground connections. May simply be a loose ground wire somewhere... More common than one would think, but the ground path is every bit as important as the positive side.

Not even sure where the sensor mounts on that one. Could whatever triggers it have an issue? As for checking it, Might consult the shop manual, has to be a test for it. I'd think it's some kind of Hall Effect sensor, best tested with an oscilloscope I suspect, Thinking if it's in an area metal shavings or debris might collect, they could interfere. Or if the mouning bolt was simply loose? (it might ground through the mounting...) May be it's just bad and breaking down from heat? Don't rule out the wiring between it and the speedo or possibly the speedo itself.

I would go through and clean all the ground connections


I Have to go with Old Guy.

Clean your Battery connections like you`ve never done before.
Then Tighten them , like you`ve never done before.
And, Check the wiring between the Speedo sensor and speedo.
292330
 

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Discussion Starter · #10 ·
All good stuff, thanks a lot.

Defiantly an electric speedo. Starting to wish it was a simple, wheel mounted cable.
 

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Is it a factory unit?
It may be an add on electric unit.
I cant see it on your dash area.
 

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Discussion Starter · #13 ·
Not 100% sure, but it feels factory. The speedo is embedded on the top of the headlight housing, and the sensor seems to belong where it is mounted.

It’s almost horizontal, slightly tilted toward me. Had to mount the faring high enough so that I could see it (below the radio, above the handlebars).
 

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Discussion Starter · #14 ·
I’ve seen a few threads on this forum about how to replace the sensor, but nothing about the diagnostics that led them to think it needed replacing.

Once I’m able to try all of the stuff on this thread, and rule everything else out, I guess I can start throwing parts (new sensor) at it. The TrailVoy forum has been a godsend for my Trailblazer over the past 15 years......I have faith that someone here has had the same experience with the speedo and can help me pinpoint the issue.
 

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Check ALL the ground and power connections, not just at battery, engine ground connector, frane ground points, positive cable -both ends. etc. And I am assuming the speedo is original,,, wasn't it in the headlight to start with?

P.S., when you get a chance, Would you take a good pic of your shifter? I have the Aero floorboards on my Ace T and am wondering about the shifters as they are different numbers..Don't know what's different. Brake pedals are definitely different, I didn't change mine though.
 

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Discussion Starter · #16 ·
You’re right.... the speedo is original (mounted on the headlight). Double checked the service manual, and it matches up (along with the sensor and location).

I’ll try to get pics tomorrow, it was nasty today. Not real keen on taking the cover off in the pouring rain and 30 degree temps.
 

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In mounting the fairing, maybe a ground got disturbed?

I wish it was raining,,, its 0 Farenheit outside and heading for maybe 10 below with snow starting in the AM
 

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Discussion Starter · #18 ·
The faring just clamps to the forks. Radio power is sheathed in a flexible conduit under the tank and seat. 12v to the positive on the battery, ground to a solo bolt under the seat, and acc wire to the signal fuse (don’t have signals on the bike, anyway.). I’ll double check those when I’m combing through all the other stuff in this thread, for sure.

Closer pics of the shifter and rear brake. 405277FF-23EF-4726-9609-9375771F286A.jpeg B3FE6FAE-1AC6-4AD9-A23F-45C144CC0F8E.jpeg
 

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How about a side view of the shifter? Interested in height above floorboards. That looks close to mine in shape but appears to be even higher off the boards. The one on my old Nomad had the rear part down at board level so all you had to do to upshift was slide your foot back. I kinda liked it that way.

side note: I had those same highway pegs, while tracking down a vibration felt in the seat, I determined those, being mounted to the normally isolated engine mount bolt and resting on the frame, were transferring vibrations to the frame.

Tourer shifter with Aero boards. front top of board to top of shifter approx 3", rear 2-1/4" :

292344
 

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Discussion Starter · #20 ·
I’ll get some more pics when it stops raining (again).

The heel shift is placed perfectly, foot flat on the floorboard and a subtle push with the back of my foot. Downshifting, another subtle slide forward and easy push down with my toe. Only time I use my toe to pull up is when shifting into neutral.
 
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