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Tach gone wild...

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The tach on my '82 1100G has started to drift +/- 1K or so without me changing the RPM. Seems steady below approx. 4K, but when travelling down the road at higher revs, it starts to wander.

Never had this issue before & I thought it was a sticky cable - bought some chain/cable wax and lubed up both the tach & speedo cables. Didn't make a difference, still seems to have a mind of its own.

Any ideas as to what's going on?? I REALLY don't want to tear open the gage if I don't have to. Hopefully someone out there has experienced this before.

Thanks!!

Mike
 
Is it making any noise? Both the tach and the speedo on my bike's new gauge cluster had a lot of needle flappage when I first put the cluster on the bike. I sprayed some WD40 in to the cable hole and reattached the cables...After a few minutes of riding the noise from the gauges went away and the needles stopped flagging.
 
If the tach is gear driven off of the cams, how would clutch slippage affect it? The sound of increasing revs would probably be noticeable.
 
Cables can wear out and hang up and make the tach jump about. Take the cable off and pull out the inner cable and check it for frayed wires. If not clean the inside of the cable tunnel and check if it turns smoothly. If it's not the cable these tacks are also junk. I've put three on my bike already and this one jumps about also.
 
How many miles on it?

Tachs and speedos work on the magnetic drag of a cup surrounding the base of the indicator needle shaft. If the cup is brushing the needle, it'll jump up. Over time, it could have worn or gotten dirty enough to drag.

You could test it by driving the tach with a variable speed drill. If it's still jumping, the problem is in the tach. If it is smooth, the problem is in the cable.
 
Thanks for all the responses guys:

Dave, I too thought the clutch might be slipping & causing the jumping; however, it does it when just reving the engine in neutral too.

I like the variable speed drill test to discern which component is the culprit - hadn't thought of that one!

I did pull the clutch cable before & it looked good, no frayed wires and seems to spin quite freely. Lubed it with chain wax.

The bike has ~27K on it, so as Chef pointed out, perhaps it's just the end-of-life of a junky tach.

I'll try spraying silicone in it as a last ditch effort to remedy the problem - I'll let you know what happens!

Thanks again,

Mike
 
Chain wax is "sticky" so it can stay on the chain longer without slinging off. I've never found it to be a good candidate for cable lube. Silicone works, or dedicated cable lube is best. A friend of mine swears by graphite, but I don't know what that would do to the seals so I haven't tried it.
 
hikermikem said:
Thanks for all the responses guys:

Dave, I too thought the clutch might be slipping & causing the jumping; however, it does it when just reving the engine in neutral too.

I like the variable speed drill test to discern which component is the culprit - hadn't thought of that one!

I did pull the clutch cable before & it looked good, no frayed wires and seems to spin quite freely. Lubed it with chain wax.

The bike has ~27K on it, so as Chef pointed out, perhaps it's just the end-of-life of a junky tach.

I'll try spraying silicone in it as a last ditch effort to remedy the problem - I'll let you know what happens!

Thanks again,

Mike
Click to expand...


Well, I siliconed the inside of the tach several times, each before riding a bit to work it into the guts well - certainly seemed to help, my tach jumps around a whole lot less now, and even seems to be more accurate. Still has a little "nervousness", but the silicone made it usable again.


Mike
 
hikermikem said:
Thanks for all the responses guys:

Dave, I too thought the clutch might be slipping & causing the jumping; however, it does it when just reving the engine in neutral too.

I like the variable speed drill test to discern which component is the culprit - hadn't thought of that one!

I did pull the clutch cable before & it looked good, no frayed wires and seems to spin quite freely. Lubed it with chain wax.

The bike has ~27K on it, so as Chef pointed out, perhaps it's just the end-of-life of a junky tach.

I'll try spraying silicone in it as a last ditch effort to remedy the problem - I'll let you know what happens!

Thanks again,

Mike
Click to expand...

Hey Mike, what happened?
 
Where the tach needs to be lubed is between the part that spins with the cable end and the tube around it. They rattle around like a bad bearing if they go dry too long. Turn it upside down and oil it, spin it, oil it, spin it.....Use a thicker oil so it stays in there for a while...
Speedos work the same way, can't hurt to oil that too.
 
tkent02 said:
Where the tach needs to be lubed is between the part that spins with the cable end and the tube around it. They rattle around like a bad bearing if they go dry too long. Turn it upside down and oil it, spin it, oil it, spin it.....Use a thicker oil so it stays in there for a while...
Speedos work the same way, can't hurt to oil that too.
Click to expand...

I'm not sure I'm understanding where/what portion of the tach you're referring to. I've got a feeble mind & sometimes it farts...

Can you try explaning this again?? I'm still looking to get this tach to settle down.

thanks,

Mike
 
hikermikem said:
I'm not sure I'm understanding where/what portion of the tach you're referring to. I've got a feeble mind & sometimes it farts...

Can you try explaning this again?? I'm still looking to get this tach to settle down.

thanks,

Mike
Click to expand...

Take the tach cable off and look at where it was attached. There is an outer threaded tube, and an inner part with a square hole for the inner cable end to go in. This part gets spun by the cable. Turn the tach upside down, oil the gap between these two pieces. They are fairly long, the oil will go down in there over an inch, maybe closer to two. Don't use WD-40, it only lubricates for a little while, not really a lubricant. Use some type of oil thin enough to go down into the tube yet thick enough to stay there once it's in. I've used several different types of oil on several different tachs, doesn't seem to matter really. It's not a high temp high load part, it just sits and spins fairly slowly but it does need something. Sewing machine oil, motor oil, whatever.
 
I'm going to Lowes and get some penetrating oil with tiny Teflon balls in it.
The stuff is made by Blaster.

If I understand this correctly the cable doesn't directly drive the Tach. It spins a magnetic cup or something like that, this imparts the rotation to the Tach. gearing movement.
Is that how it works?
 
Last edited:
tkent02 said:
Take the tach cable off and look at where it was attached. There is an outer threaded tube, and an inner part with a square hole for the inner cable end to go in. This part gets spun by the cable. Turn the tach upside down, oil the gap between these two pieces. They are fairly long, the oil will go down in there over an inch, maybe closer to two. Don't use WD-40, it only lubricates for a little while, not really a lubricant. Use some type of oil thin enough to go down into the tube yet thick enough to stay there once it's in. I've used several different types of oil on several different tachs, doesn't seem to matter really. It's not a high temp high load part, it just sits and spins fairly slowly but it does need something. Sewing machine oil, motor oil, whatever.
Click to expand...


Thanks tkent02 - I get it now.

Now. if only I can find someone to help me turn my bike upside down so I can lube the tach...
 
normGS750 said:
If I understand this correctly the cable doesn't directly drive the Tach. It spins a magnetic cup or something like that, this imparts the rotation to the Tach. gearing movement.
Is that how it works?
Click to expand...

Correct. It's called a drag cup, the faster it spins the farther around it pulls the needle.


hikermikem said:
Thanks tkent02 - I get it now.

Now. if only I can find someone to help me turn my bike upside down so I can lube the tach...
Click to expand...

Two cotter pins, the tach comes off in your hand. Leave the wires hooked up.
 
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