speed sensor

[41107]

should i have continuity on the brown and yellow wire to the speed sensor,thru the coil that is?
1985 k 100 rs

[roy]

Are you talking about the sensor on the final drive? If so connect a voltmeter across these leads and spin the rear tire. You should get a pulsing millivolt signal form this pick-up / sensor.

Roy

[cjack]

Ok on the millivolts. You will also get about 3000 ohms on your multimeter when measuring conductivity. If you hold a soldering iron (turned on) or other source of 60 Hertz magnetic field near it (removed from the drive) then the speedometer, if everything is working, will indicate 45MPH.

[41107]

You guys are fantastic.Did the soldering iron trick.Speedo shows 45 mph.It's time to put things back together and go for a ride.

[41107]

Well.put things all back together went for a short ride around the block.No speedo.The needle bounces at times and i've seen it going to 40 mph while just costing.Prior to it all i assumed the usual contact situation in the cluster.Took it all apart and cleaned and bend the contacts(rotationaly).Applied a minute amount of copper antisize to them and reassembled.Did the same with wire loom connectors(clear and green) on the outside.Everything in their seemed in good codition from what i could see.All this because some time ago when the speedo went i simply gave it a wack and it was fine again.Double checked the ohms reading again on the clear outside connector to the speedo and have a good signal.There is one other thing i thought i mention,my turnsignals dont auto-cancel anymore.Thats where the idea came about the pickup coil in the final drive.I have Haynes manual but it's realy useless when it comes to this kind of stuff. Confused.

[cjack]

Well.put things all back together went for a short ride around the block.No speedo.The needle bounces at times and i've seen it going to 40 mph while just costing.Prior to it all i assumed the usual contact situation in the cluster.Took it all apart and cleaned and bend the contacts(rotationaly).Applied a minute amount of copper antisize to them and reassembled.Did the same with wire loom connectors(clear and green) on the outside.Everything in their seemed in good codition from what i could see.All this because some time ago when the speedo went i simply gave it a wack and it was fine again.Double checked the ohms reading again on the clear outside connector to the speedo and have a good signal.There is one other thing i thought i mention,my turnsignals dont auto-cancel anymore.Thats where the idea came about the pickup coil in the final drive.I have Haynes manual but it's realy useless when it comes to this kind of stuff. Confused.

Take a look into the pickup hole in the final drive and make sure that the toothed ring is still fastened to the crown gear. Turn the wheel and you should see the six tooths go by all in the same plane. The ring falls off sometimes. Then you have to go into the drive and refasten it somehow. If the pickup works with the soldering iron and not when the wheel turns, then the ring is probably the problem.
You can also have good looking pins in the speedo and still have intermittant connection. The only real fix for that is soldering around the pins with jumper wires.

[41107]

Took speedo apart and soldered bypass wires around the shaky connectors including the two prongs that the little circutboard with it's contacts slides over.Checked millivolts to pick-up on final drive .135mv,don't know if thats a good reading.Checked ohms resistance reads every tooth at 2835 and drops off when turning rear wheel.Again checked for continuity can not get a reading on the coil that is inside the pick-up coil on the final drive. Their must be something wrong here.Any coil should show continuity if the winding isn't broken.Checked for loose tooth ring in final drive,solid (bend my little screw driver prying on it).Tested ohms resistance to ground on all ground (brown)wires coming out of speedo.That is with speedo connected to its wire connections.Shows .400 going to battery negative.Thought maybe bad frame ground.But that reading to me is ok.What you all think?

[deilenberger]

I think you should listen to Jack and see if the tooth-ring in the rear drive is attached to the crown-gear. They have been known to come loose and give exactly the symptoms you're seeing. Since the circuit works by the soldering iron test - it's a big hint the sensor isn't seeing the tooth-ring moving.

Edit: Ah - see you did check it. Sorry. I'd suggest reading up on the cluster and fixes over on the IBMWR K-tech pages. The use of metal bearing antiseize on the internal contacts - after twisting the pins 10 degrees or so - has made some bad pods well again. It's a bit simpler than soldering jumpers around the pin connections.

Edit-2 - I see you still can't read the sensor coil itself. If your ohmmeter is working (check it against a resistor) - that indicates the coil has an open in it. Fix is replacement.

[cjack]

Took speedo apart and soldered bypass wires around the shaky connectors including the two prongs that the little circutboard with it's contacts slides over.Checked millivolts to pick-up on final drive .135mv,don't know if thats a good reading.Checked ohms resistance reads every tooth at 2835 and drops off when turning rear wheel.Again checked for continuity can not get a reading on the coil that is inside the pick-up coil on the final drive. Their must be something wrong here.Any coil should show continuity if the winding isn't broken.?

I'm confused about this where you get 2.835K ohms (of the pickup coil?) and then you say that the coil is open. Is it intermittant? When you plug it back in, the coil opens? They aren't terribly expensive. Might try a new one if that's the case.
The millivolts reading is ok. There is an amplifier inside the speedo which amplifies that to about 6 volt pulses (that little strip with the 4 pins at the bottom of the speedo).

[KCKBMOA]

I will 3rd the mention of the "trigger ring" possiblity. I did all the meter checks, and was getting very deep into the speedo, when I finally just checked the ring. Be sure it is actually mounted on it's machined surface. If you just look in the hole and spin the wheel, you may be fooled, as it will rotate just because it is still near a moving object. The oil will drag it around. With the wheel still, gently touch it with a small screw driver blade, If it moves then it is not mounted. I have been able to use the drain hole and the sensor hole to coax the trigger ring back on to it's mount. It lasted all year the 1st time, and I just did it again recently. Give it another look. KC

[41107]

I'm confused about this where you get 2.835K ohms (of the pickup coil?) and then you say that the coil is open. Is it intermittant? When you plug it back in, the coil opens? They aren't terribly expensive. Might try a new one if that's the case.
The millivolts reading is ok. There is an amplifier inside the speedo which amplifies that to about 6 volt pulses (that little strip with the 4 pins at the bottom of the speedo).

Maybe I am just to dumb to understand the inerts of this pick-up coil.i just always believed that if its a coil it should have continuity no matter what unless the coil windings are broken.I do get 2835 ohms but no continuity.So maybe everything is ok down at the pick-up but not at the amplifier?But things worked well with Your solder iron suggestion.THANKS for all your help,really appreciated.

[41107]

I will 3rd the mention of the "trigger ring" possiblity. I did all the meter checks, and was getting very deep into the speedo, when I finally just checked the ring. Be sure it is actually mounted on it's machined surface. If you just look in the hole and spin the wheel, you may be fooled, as it will rotate just because it is still near a moving object. The oil will drag it around. With the wheel still, gently touch it with a small screw driver blade, If it moves then it is not mounted. I have been able to use the drain hole and the sensor hole to coax the trigger ring back on to it's mount. It lasted all year the 1st time, and I just did it again recently. Give it another look. KC

I tested the ring by putting a screw driver thru the hole and bending the screw driver.i believe the ring is secure.

[41107]

Just an update.Took the little amplifier circuit board in the speedo out and looked it over.It shows an area of darkened (like burned) solder circuit traces on the underneath side.I think I am on to something.

[cjack]

Maybe I am just to dumb to understand the inerts of this pick-up coil.i just always believed that if its a coil it should have continuity no matter what unless the coil windings are broken.I do get 2835 ohms but no continuity.So maybe everything is ok down at the pick-up but not at the amplifier?But things worked well with Your solder iron suggestion.THANKS for all your help,really appreciated.

The coil is continuous, but only to the extent of 2835 ohms...not to 0.2 ohms like one would expect on a short wire from end to end. If you got the 45 MPH then the amp and all is good. I don't know where your problem is while running down the road. Do you get short jerks of the speedo when you rotate the wheel with the ign on, motor not running?

[41107]

Under a magnifying glass i seem to have found the problem.It"s the amplifier circuit that had a open path.Hardly noticable,good for intermittent contact.