Topic: Swinging speedo needle

[Schnell]

The usual solution for this symptom is to lube the speedo cable. I've done that but the needle is still bouncy. Is grease too heavy to use for lube? This there a dampening adjust inside the speedo?

Thanks.

[MCRider]

The usual solution for this symptom is to lube the speedo cable. I've done that but the needle is still bouncy. Is grease too heavy to use for lube? This there a dampening adjust inside the speedo?

Thanks.

If you've treated the cable, the inside of the clock needs attention. If it wa sever stored upside down, the lube runs out. Even if right side up, the lube deterirates and you get the bounce. Also, could be the drum and magnet is fouled with corrosion and needs cleaning.

I've had one apart but never fixed it myself. I've had a  speedo shop do 2, clean and lube, good as new.   But it is a DIY if you're up for it.

[Schnell]

Okay, thanks. Does anyone have a pic of the insides?

[MCRider]

Okay, thanks. Does anyone have a pic of the insides?

There are several threads with pictures on the subject. I even had one for when I disassembled the speedo. Do your "Google Custom Search" in the header.

[Schnell]

Ahh. Damping pot. Sounds like opening them is difficult to not damage the ring.

[kghost]

Ahh. Damping pot. Sounds like opening them is difficult to not damage the ring.

Yes.

Before you open it up........

Remove the speedo, place it face down, then add a couple drops of light oil to the edges of where the cable enters. Leave it for a day.

Sometimes it makes all the difference.

This is what it looks like minus the case.

[Schnell]

Thanks. Though my speedo needle moves too freely, like the vacuum gauges used to sync carbs, it needs dampening, not more lubricating oil.

[kghost]

What did you lube your cable with?

I recommend a spray white lithium grease.

[Schnell]

General purpose high pressure and temp grease, same as I used in the steering head bearings. It's quite thick. Think that could be it? I know the lithium stuff is much lighter.

Worth a try for sure. Not going to go into it.

[kghost]

General purpose high pressure and temp grease, same as I used in the steering head bearings. It's quite thick. Think that could be it? I know the lithium stuff is much lighter.

Worth a try for sure. Not going to go into it.

I prefer a lighter grease......

I really think you just need to lube the speedo as above.

Couple drops over a couple days.

Won't hurt anything as long as you don't use too much....land it costs nothing.

Try it first

[grcamna2]

I hope you do an open speedo thread on this one..,so I can learn a bit before I do mine;I need to see how you fill a damper pot on a CB400F speedo & what type & viscosity fluid is preferred.

[Schnell]

I hope you do an open speedo thread on this one..,so I can learn a bit before I do mine;I need to see how you fill a damper pot on a CB400F speedo & what type & viscosity fluid is preferred.

Well, the bigger question is whether there was ever (meant to be) any oil in that pot. Some folks believe not. If there was supposed to be, wouldn't it be sealed?

[MCRider]

IIRC: from a thread, the poster used a silicone lubricant in the damping pot. I don't think its sealed, that's why you shouldn't store them upside down.

Have you ever seen one that had oil stains around the 2 screw heads that hold the face on? That's why.

Look in the Tipis and Tricks forum I think that's where a disassembly thread is. Also, just Google it, there are a few threads cast into the ether.

[Schnell]

I wonder if someone could authoritatively address this question: is there a viscous fluid in the dampening pot from the factory? Maybe a Honda mechanic who opened a speedo for some type of work?

[MCRider]

Here's a thread with other threads buried in it.
http://forums.sohc4.net/index.php?topic=61527.0

and more
http://forums.sohc4.net/index.php?topic=97378.0

This thread opens on page 3. Where it talks about lubing. Scroll down and toggle to earlier and later pages
http://www.salocal.com/sohc/tech/speedo/spedo3.htm

[MCRider]

I wonder if someone could authoritatively address this question: is there a viscous fluid in the dampening pot from the factory? Maybe a Honda mechanic who opened a speedo for some type of work?

PM "Lecram" he's the expert, can do the work and supply the pieces.

He does it for pay, but I think he would answer your question also.

[Dave Voss]

One thing to remember, is that the speedometer needle movement is a slave to the spinning of the cable.  If the speedometer needle is bouncing, then the cable is not spinning at a consistent rpm, but rather it is likely winding up a bit, and then releasing a bit, over and over while spinning.  If the cable or the sheath are worn enough to create additional friction somewhere along the length, then the cable rpms can oscillate, thereby causing a bouncy speedometer needle.  Even new properly lubed cables can oscillate if the routing has any spots where the cable is binding a bit too much inside the sheath.  Some speedometer cables and sheaths develop wear spots that no amount of lubing can fix, and the only solution is to replace both, which is easy since they are readily available and relatively inexpensive.

Also, the speedometer (and the tachometer) is internally damped to help extend the life of the instrument against the vibration that is present in motorcycles, rather than to help steady the needle when driven by a cable that is oscillating.  I've taken several speedometers apart, some that looked pretty bad on the outside, but the damping action of the needle was still functional, so I would make certain that the issue isn't with the cable before experimenting with the speedometer itself.

One quick test for the speedometer is to remove it and temporarily spin it using an electric drill, if the needle climbs to a certain steady speed indication, then it's probably without issue.

[Schnell]

True that. Thanks.

[MCRider]

One thing to remember, is that the speedometer needle movement is a slave to the spinning of the cable.  If the speedometer needle is bouncing, then the cable is not spinning at a consistent rpm, but rather it is likely winding up a bit, and then releasing a bit, over and over while spinning.  If the cable or the sheath are worn enough to create additional friction somewhere along the length, then the cable rpms can oscillate, thereby causing a bouncy speedometer needle.  Even new properly lubed cables can oscillate if the routing has any spots where the cable is binding a bit too much inside the sheath.  Some speedometer cables and sheaths develop wear spots that no amount of lubing can fix, and the only solution is to replace both, which is easy since they are readily available and relatively inexpensive.

That's only partially true. For sure the cable must be in good shape. It drives a spinning magnet. The magnet sets up an eddy current that drags a cup with a needle attached. The magnet is not fixed to the cup but spins freely inside it. So its not a mechanical slave relationship. If something is interfering with the eddy current like corrosion from years of condensation cycles, or interfering with the smooth movement of the cup like lube or even outright damage, the needle will not move smoothly regardless of how good the cable is.
http://www.explainthatstuff.com/how-speedometer-works.html

Scroll down this link to the best diagram I have seen, with bullet points explanation.

I don't have the first hand answer to the question about viscous lube in a cup, but my money is on just that. The rotating cup needs lube and the lube doubles as a dampiing medium to take the bounces out.

[Dave Voss]

It drives a spinning magnet. The magnet sets up an eddy current that drags a cup with a needle attached. The magnet is not fixed to the cup but spins freely inside it. So its not a mechanical slave relationship.

Yes, I'm aware of all that, and you make a good point, but my point was that the cable provides the input (be it smooth or not so smooth) that the speedometer reacts to, and therefore the speedometer is a 'slave' to the cable, whether thought of as mechanical or not.

If something is interfering with the eddy current like corrosion from years of condensation cycles, or interfering with the smooth movement of the cup like lube or even outright damage, the needle will not move smoothly regardless of how good the cable is.

Yes, that can happen, but barring any physical contact between the magnet and the cup, the magnitude of effect that a disturbance in the eddy current can cause is less than the magnitude of effect that an oscillating cable (and therefore oscillating magnet) can cause, so it's important to be certain that the cable and sheath are in good condition, adequately lubed, and properly routed before suspecting the speedometer's internals.

[grcamna2]

What's the correct Spec. type of lube to use on a speedometer cable ? plain grease ?