Weird speedometer issue

[amamet]

so i have an issue where my speedometer doesn’t like to go past 40mph-ish.  Had the trans rebuilt years ago by Charlie Cole, one of the last he did, and the issue started right after installation. New cable was installed at the time.  Today i threw in 3 other speedometers, all being brand new, and all act the same.  Can it be the cable?  If it’s something in the Speedo drive what piece should i check to see is missing?  Maybe something didn’t get installed correctly at installation time.
Thanks
Allen

[guzzisteve]

Don't know how it would act but maybe ball bearing gone letting it slip. I have not run one w/o a ball.. Isn't much in there

[wirespokes]

This is a five speed? I know enough about them to make a guess. I think Steve has the answer - up to 40 there's enough friction for the worm drive to not slip. After that, it can't keep up. As for how to replace the ball bearing, it might be possible to fix by only pulling the swingarm. Nothing else makes sense to me, there's no way a cable could cause those symptoms, which leaves the worm drive in the transmission 'locked' to the shaft with a ball bearing.

[Kiwi_Roy]

When you say Ball Bearing are you referring to a race or just a single ball that acts like a key?
I seem to recall something similar happened to my bro when he overhauled the gearbox on his guzzi

[nc43bsa]

It's a single ball that locates the drive gear on the shaft.

It commonly escapes and runs for freedom when disturbed.

[Kiwi_Roy]

It's a single ball that locates the drive gear on the shaft.

It commonly escapes and runs for freedom when disturbed.

I imagine to get one back in place its drop the driveshaft and take of the coupling until you gain access to the worm gear.

[Wayne Orwig]

Can you turn the cable inner piece at the speedometer? Maybe you can feel or hear it slipping somewhere and track where it apparently is slipping.
Pull the drive gear out of the top of the transmission and inspect it. Verify that it is OK where it engages the cable.

Odd.

[Kiwi_Roy]

Can you turn the cable inner piece at the speedometer? Maybe you can feel or hear it slipping somewhere and track where it apparently is slipping.
Pull the drive gear out of the top of the transmission and inspect it. Verify that it is OK where it engages the cable.

Odd.

I doubt you would be able to turn it, it's a gear and worm, too much of a ratio change

[amamet]

I realized somehow the speedo cable is not the lemans 1 one, neither is the tach cable. I just ordered a set from mg.  I bolted my speedo to a c-stand (a piece of film gear that does everything, everyone should have one). no idea how I installed the wrong cables, but oh well.  anywho, with the bike on its centertand and the speedo in a stand with no kinks on the cable, the needle moved smoothly and past 40 easily.  i didn't want to go any further than that with the bike just on its center stand. once I get the new cables ill try it out.  at least I know how to check for and replace that steel ball in the trans.  if I have to, ill do it over the winter

[Wayne Orwig]

I doubt you would be able to turn it, it's a gear and worm, to much of a ratio change

That is my point. If it turns, something is slipping.

[wirespokes]

I'm not following you.
Maybe it's because I don't know what a C Stand is, or what is accomplished using it.
Are you saying the speedometer works normally when not on the bike, yet still attached to the cable and transmission?

If that's the case, it's just possible, without the bends in the cable, there's less friction and the 'slipping point' is higher.

I can't see how the wrong cable could power the speedo up to 40 and then bug out. It either connects or it doesn't.

I'll bet something happened to the locking ball bearing for the drive.

Removing the swingarm, and then the output shaft retaining nut will allow access. It might be a bit fiddly removing the nut, but I think it could be done with the transmission in situ.

[Tom H]

Maybe it is the cable??? Why...

If the "new" cable inner cable was cut too short or the outer too long. With the bends in the cable when installed maybe the tip is just in the drive gear and at speed it may be slipping out. With the cable straight, the inner may be staying in the gear.

Many moons ago I bought a speedo cable and the inner looked short when coiled up. Uncoiled it and the inner looked longer.

Just a thought,
Tom

[blackcat]

I'd just use a drill on the end of the cable and crank it up to a 100mph to rule out any problems north of the transmission.

[ridingron]

I realized somehow the speedo cable is not the lemans 1 one, neither is the tach cable. I just ordered a set from mg.  I bolted my speedo to a c-stand (a piece of film gear that does everything, everyone should have one). no idea how I installed the wrong cables, but oh well.  anywho, with the bike on its centertand and the speedo in a stand with no kinks on the cable, the needle moved smoothly and past 40 easily.  i didn't want to go any further than that with the bike just on its center stand. once I get the new cables ill try it out.  at least I know how to check for and replace that steel ball in the trans.  if I have to, ill do it over the winter

 

  c-stand:

 https://en.wikipedia.org/wiki/C-stand#:~:text=In%20film%20production%2C%20a%20C,in%20front%20of%20light%20sources.

[amamet]

A c-stand is a universal stand used in the films/photography world. You can do and hold anything with them.  Lights, equipment,  heavy stuff, light stuff etc..  fully articulating…. I work in film so i got mine years ago.  You can find them on fb marketplace.  A bunch of attachments as well