Speedo Works, but its reading too fast....

Alright the weekend is quickly approaching and its gonna be time to fix something new on my bike. My speedometer works but the problem is it seems to be too sensitive. when im going probably 30 it says im going 50-60. when im going 50-60 forget about it. my speedo reads up to 80mph but it might as well be telling me im going 140mph when im on the highway.

i guess i need help on troubleshooting this whole problem. what should i check for first.

I can say that the existing speedo cable does look pretty crappy. it has electrical tape on it in some spots. and the protective coating is actually gone on some small spots and i can see a little rust. if my speedo is acting the way it is should the first thing i do is just replace the cable? if you want pics of anything just say the word.

thanks.

 

Re: Speedo Works, just not well...

If the cable is questionable, you really need to replace it/ This will eliminate it as a possible cause of your problem.

 

Re: Speedo Works, just not well...

my speedo quit working about a month ago so I first replaced the speedo cable but that didn't fix it so next i bought a gear unit assy and replaced that and now my speedo works fine. Its all process of elimination but i would definately replace the cable first since its the cheapest replacement. If that doesn't fix lok up kingpowersports.com they are in new york and i got a drive unit assy for $30 with shipping so thats a good deal.

 

Re: Speedo Works, just not well...

ok im gonna order a new speedo cable then. i took a look at where they connect at the speedo and down at the wheel. and just to make sure you remove it from these locations correct?

 

Re: Speedo Works, just not well...

Yup. Remove the bolt that holds the lower end to the gear drive and slide it out. The other end just unthreads from the back of the speedo.

But if it works, just doesn't register "right", it doesn't sound like a cable issue to me. The cable should either work or not. If it spins freely in the cable housing and isn't broken, that's about all that can go wrong with it. It's not like there are a bunch of moving parts. Just a flexible shaft (cable) and a housing.

 

Re: Speedo Works, just not well...

i agree with willierides that if it does work just not correctly it probably isn't the cable but for around $10 you can replace it and since you said your cable looks bad anyways you might as well replace it but me personally i think it would probably be the gear drive unit assy.

 

Re: Speedo Works, just not well...

Reading fast does seem odd, but certainly easy enough to swap out.
Speedo cables do cause trouble AND continue to function. No/old/bad lube can cause the needle to jump huge ammounts, or just fluctuate 10 or 15mph, or vibrate (more than just engine vibration) a couple miles per hour.
Relubing an old worn cable may get just a few more miles or maybe thosands more. No telling until it is dead.

 

Re: Speedo Works, just not well...

If it is consistently reading to fast the speedometer itself is bad. The cable and drive gear can only turn as fast as the wheel turns.

 

Re: Speedo Works, just not well...

Who the heck needs a spedo anyway!!!
I have not had a working one in months.

BTW anyone got a working cluster LOL

My vote goes to the gear assy being the problem OR maybe you are really going that fast and dont know it

 

Re: Speedo Works, just not well...

Open the Speedo.
Look for the Bearing Bushing that the Bell-shaped object rotates in.
Add a drop of Sewing Machine Oil or a drop of light oil from a precision oiler to that bearing.

The only force that moves that bell-shaped object is a weak Magnetic Field.
It needs to be able to rotate within that bushing without friction.

The slightest hint of drag will throw-off the speed reading by a good deal.

 

Re: Speedo Works, just not well...

ok well i took the existing speedo cable off and checked it out. it turns fine and pretty easy but i went ahead and put some Tri-Flow lube in it just to make sure and put it back in drove around with a bluetooh inside my helmet and had my gf read out the mph as we drove around. it seems that my speed is 10mph too fast when we are going slow. when we are going at a medium pace its off by about 15 and if we go about 45-50mph it off by about 30mph.

the needle does not jump around at all and it moves smoothly. it just seems to be too fast.

so now im doubting if i really want to order that speedo cable and if i should just go straight to the gear assembly. but then i ask you this. would a bad gear assembly make th reading too fast? almost makes me wonder if my actual Speedometer is just not working correctly. anyway to adjust a speedo's readings?

edit note: crap sorry i typed this up and had my response sitting here while i went and tested all this then hit submit not seeing that rick and the others responded with similar things i was thinking.

hahah i agree ass.fault. but i absolutely love turns and twisties and its really bothering me that i can't have the accurate knowledge of how fast im hitting them.

ok i will do this. this (obviously) will be another first for me. do i have to remove the whole instrument cluster off the bike to do this. or can i do this while its mounted. please say mounted haha.

 

Speedo error is nothing new on bikes this old. Speedo itself can often be the problems. They work with magnets and can lose their precision after a bit of wear gets to them

But, I'm surprised nobody has asked the obvious yet.

Reading fast, IMO, points towards a smaller wheel/profile tire on the front with a drive gear to suit the larger original.

My 550 used to read wrong till I worked out the forks werew 1mm smaller than stock. Someone had had a bingle in the past and replaced the whole front end, including a smaller wheel.

What size rim and tire do you have on there?

 

when i had to replace my drive unit my speedo did not work at all sometimes and others it would work fine it was just hit and miss but i don't believe it was ever reading the wrong speed when it was working. It eventually just quit all together and once i put the new drive unit on there it worked fine. I do have to agree with hired_goon though that a smaller tire on the front will turn quicker therefore making the speedo show you are going faster than you actually are so i would definately check that out.

 

ill go measure them and post the size

 

are you sure its not in km/h????

 

You could just read it off the tire sidewall.

 

My 82 750 speedo reads 10- 15 miles slower than i am actually going. I replaced the cable and that didn't make a difference. Have not tried anything else yet.

 

My 82 750 speedo reads 10- 15 miles slower than i am actually going.
I replaced the cable and that didn't make a difference. Have not tried anything else yet.

 

Maine82Maxim750 Let me know if you find out what it is my 82 750 is reading 15 -20mph to slow also.

 

A small permanent magnet affixed to the rotating cable interacts with a small aluminum cup (called a speedcup) attached to the shaft of the pointer on the analogue instrument. As the magnet rotates near the cup, the changing magnetic field produces eddy currents in the cup, which themselves produce another magnetic field. The effect is that the magnet 'drags' the cup -- and thus the speedometer pointer -- in the direction of its rotation with no mechanical connection between them.

The pointer shaft is held toward zero by a fine spring. The torque on the cup increases with the speed of rotation of the magnet (which, recall, is driven by the bikes front wheel) Thus an increase in the speed of the bike will twist the cup and speedometer pointer against the spring. When the torque due to the eddy currents in the cup equals that provided by the spring on the pointer shaft, the pointer will remain motionless and pointing to the appropriate number on the speedometer's dial.

The return spring is calibrated such that a given revolution speed of the cable corresponds to a specific speed indication on the speedometer. This calibration must take into account several factors, including ratios of the tailshaft gears that drive the flexible cable, the final drive ratio in the differential, and the diameter of the driven tires. The speedometer mechanism often also drives an odometer plus a small switch that sends pulses to the vehicle's signal cancellation relay.

You might have a broken spring in the Speedo Head. You have to actually take the instrument off and look to see.

I'd start looking for a Speedo on eBay.
The labor to replace the return spring would be more than the cost of a good used speedo head.