Topic: Speedo likes to "flutter" above 40 mph.

[LiveeviL81]

Hello all,
I recently got my CB750A back on the road and running, and with all the changes made I am not sure where to start on this bothersome issue.
According to my friend following me, the Speedo is accurate to about 40 mph, after which it'll float/flutter between 40-60mph and around 70 mph the flutter is between 60-85mph. It's not consistent, and didn't occur before, but I did switch to reverse comstar wheels, keeping my drive unit, along with opening the speedo and swapping out the bulbs for little LED's. Not sure if its a cable issue, speedo issue, or in the front wheel drive.

Thoughts?

[willbird]

Hello all,
I recently got my CB750A back on the road and running, and with all the changes made I am not sure where to start on this bothersome issue.
According to my friend following me, the Speedo is accurate to about 40 mph, after which it'll float/flutter between 40-60mph and around 70 mph the flutter is between 60-85mph. It's not consistent, and didn't occur before, but I did switch to reverse comstar wheels, keeping my drive unit, along with opening the speedo and swapping out the bulbs for little LED's. Not sure if its a cable issue, speedo issue, or in the front wheel drive.

Thoughts?

Can you make up something to allow driving the speedo with a hand drill ?? I had a K2 speedo handy that came from Ebay and a small screwdriver bit which is .136" in dia. Quick google gave me 3mm (.118") as the dimension of the normal square end on a speedo cable. #2 square drive for screws is dimension 0.111"–0.1126" I bet a little hand grinding of one would make a bit that fit well enough. https://m.media-amazon.com/images/I/51Rx0Q8Uw0L._AC_SX679_.jpg

1600 RPM with a Ryobi drill gave me 40 mph on the speedo...the needle on this one had a little jerk to it now and then.

[MauiK3]

Take a close look at the cable, it might be having problems

[PeWe]

I guess it is the dampening fluid inside that has leaked out.
I think that can happen if gauge is stored upside down.

My NOS K2 speedo I bought  late 2018 is very happy most of the time with a swinging needle.
Worse after 100kmh.

Last ride, I had to look at the tacho that has a stable needle.
At 8000rpm, 5th gear, speedo was jumping around 180kmh.

Checked the gearing excel chart for CB750,  17:48, stock rear tire. 8000rpm = 188kmh

[CycleRanger]

Take a close look at the cable, it might be having problems

This. The speedo on my XS650 started "fluttering" just before the cable bound up then released and wrapped the needle all the way around and tweaked the gauge.

[Ujeni]

• Remove the speedometer cable from the bike
• Separate the inner metal cable from the outer plastic housing
• Clean both with solvent to remove old grease and grime
• Lubricate the inner cable and the inside of the plastic outer cable
• Reassemble the speedometer cable
• Reinstall the cable and go for a test ride

If you have the same problem, then it is time to move onto the speedometer gear housing on the front wheel and the speedometer itself. Most often though, it is the cable.

[scottly]

It's not consistent, and didn't occur before, but I did switch to reverse comstar wheels, keeping my drive unit,

Do you mean you kept your drive from a spoke wheel, which is on the right side, on a Comstar wheel which normally has the drive on the left side?? You need to use the Comstar drive with a Comstar wheel.

[M 750K6]

• Remove the speedometer cable from the bike
• Separate the inner metal cable from the outer plastic housing
• Clean both with solvent to remove old grease and grime
• Lubricate the inner cable and the inside of the plastic outer cable
• Reassemble the speedometer cable
• Reinstall the cable and go for a test ride

If you have the same problem, then it is time to move onto the speedometer gear housing on the front wheel and the speedometer itself. Most often though, it is the cable.

Lubricate with grease on speedo and tacho drives, keeping the male part that feeds into the meter, clear of grease.

[rotortiller]

Either the cable or damper fluid. I had one that the inner cable was a bit too long and loaded the drive in the speedo. I put a small washer under the cable flange to make the outer portion longer. Usually when damper fluid goes tits-up the needle bounce gets worse in cold weather.

[LiveeviL81]

It's not consistent, and didn't occur before, but I did switch to reverse comstar wheels, keeping my drive unit,

Do you mean you kept your drive from a spoke wheel, which is on the right side, on a Comstar wheel which normally has the drive on the left side?? You need to use the Comstar drive with a Comstar wheel.

No, my CB750A had Silver Comstar Wheels, I swapped them out with some black Reverse Comstar wheels. Everything was easily bolted up, But I wasn't sure if I missed something small?

I will try to grease/lube the cable and see how that goes, thanks!

[LiveeviL81]

Greased and lubed up the cable, and it was much better initially, but started bouncing more and more over the 2 hour ride. Also noticed when reving at a gas station that the flutter would appear even at zero wheel speed. So I'm guessing the speedo unit has an issue as well. Gonna purchase a new cable and look into the speedo, Is there a good write up for cleaning up the speedo unit?

[newday777]

Pull out the inner speedo cable and inspect it.
Any stretched areas? Any rust?(if the outer sheath is rusted, it will grow rust inside squeezing the inner cable causing fluttering of the speedo.

[Ujeni]

The flutter happens when the front wheel is not turning? Can you confirm?

If so, that means the root of your problem is not the cable, but rather the speedometer unit itself.

[LiveeviL81]

The flutter happens when the front wheel is not turning? Can you confirm?

If so, that means the root of your problem is not the cable, but rather the speedometer unit itself.

Yes, that is what I noticed at the gas station, reving the engine in neutral caused some flutter. I have yet to take apart the speedo though. It also seems to flutter more on bumpy roads.

[Ujeni]

Sounds to me like the damping fluid in your speedometer is low or dried up.