speedometer gearbox/cable -- what's wrong and how do i fix it?

maylar said:

Can the UK style grease fitting on the speedo box be easily replaced with a US style? I have a grease gun but it won't snap onto the Smiths fitting.

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good question. (gawd I hope I got this right) -- I would think you would need to know the UK thread size of the original zerk fitting. chances are you would have to drill and re-tap for the next largest size - M5 (???) I may be out in left field, but it looks like my original smiths is a 2BA thread. a 10-32 does screw into it but binds up after a couple threads. on my amal carbs I did replace the original 2BA screws with M5 cap screws - thread pitch is near identical, and only .010 larger, overall diameter. problem is, to re-tap, you would have to disassemble the whole speedo-drive mechanism for the mod. not sure that's worth the effort unless you're rebuilding the assembly.

looks like i'm going with marine grease - I have a .018 hypodermic needle attachment on a mini-grease gun (loaded with marine grease). for as often as it needs servicing, probably just as easy to unscrew the grease fitting, giving it a couple pumps, and re-install the fitting.

If I have to jamb a 10-32 in there I could live with that. Gonna bring an old drive to my local NAPA and see what they can come up with.

My push type grease gun does fine on the original nipple. Also works on the rear brake nipples. There no "snap" engagement needed with that gun as you have to push quite hard to get flow and that makes a good enough seal. It is also the type of gun showing in the Haynes manual for our bikes (so that will satisfy the purists amoung us).

maylar said:

If I have to jamb a 10-32 in there I could live with that. Gonna bring an old drive to my local NAPA and see what they can come up with.

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10-32 should be readily available. I might look into a "no-ball" zerk fitting and just use a silicone dust cap. I could re-drill the fitting for the .018 needle, and.... DAMN - starting to put way too much thought into this -

You can buy a Zerk in 2BA but be careful. Mine were slightly longer than the stock one and will interfere with the long drive gear. I had to make a spacer out of a small aluminum washer.

joe czech said:

good question. (gawd I hope I got this right) -- I would think you would need to know the UK thread size of the original zerk fitting. chances are you would have to drill and re-tap for the next largest size - M5 (???) I may be out in left field, but it looks like my original smiths is a 2BA thread. a 10-32 does screw into it but binds up after a couple threads. on my amal carbs I did replace the original 2BA screws with M5 cap screws - thread pitch is near identical, and only .010 larger, overall diameter. problem is, to re-tap, you would have to disassemble the whole speedo-drive mechanism for the mod. not sure that's worth the effort unless you're rebuilding the assembly.

looks like i'm going with marine grease - I have a .018 hypodermic needle attachment on a mini-grease gun (loaded with marine grease). for as often as it needs servicing, probably just as easy to unscrew the grease fitting, giving it a couple pumps, and re-install the fitting.

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I just slather mine with moly grease at every tire change.

Information I picked up from this thread made me re-examine the relationship of my speedo drive to the hub cover on my current build. Using a feeler gauge I found the clearance between the speedo felt washer retaining ring and the hub cover to about .008".; all other parts mentioned in this post and listed in the parts fiche are present, so I'm thinking that at some point the drive housing may have taken a slight bow, but I don't have the brass to risk trying to press it a bit flatter, even with the possible bow the rear wheel spins freely.

I went looking for a shim that would fit over the distance piece that lives between the bearings; I struck gold. I found a bag of stainless washers, they measure: OD: .8560, Width: .10, ID: .670, Thickness: .030, they fit perfectly over the the long end of the distance piece and give me a clearance between the drive and the hub cover that keeps the two at a comfortable distance.

I have over 90 of these, if you would like one send me a self addressed envelope and I'll post it back to you at no charge for the shim.

Best

I simply put mine in a wood vise, with a cut piece of round wood stock on the fork side of the drive, and gently pressed it in with screwing in the vise. Examined. Repeated until straight.

Hi Joe,
Thanks for the picture of the individual components. Excellent reference.
Just for clarification, which parts did you replace (other than the cable)?

L.A.B. said:

It's impossible to say by looking at the photo.

If the cable can be inserted into the ferrule without much effort then for whatever reason the crimp probably wasn't tight enough.

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This happened with my replacement cable. The crimping failed. I pushed it back in and glued it with araldite and it has been fine for a few years now.

gortnipper said:

I simply put mine in a wood vise, with a cut piece of round wood stock on the fork side of the drive, and gently pressed it in with screwing in the vise. Examined. Repeated until straight.

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The .030 shim I added removed my concern about the drive housing rubbing against the hub cover. My drive housing doesn't have an obvious shape deformity, so, IMO the risk of breaking the housing isn't worth the anxiety of cranking the vice. I do appreciate your suggestion, and thank you for offering it.

Best.

RoadScholar said:

Using a feeler gauge I found the clearance between the speedo felt washer retaining ring and the hub cover to about .008".; all other parts mentioned in this post and listed in the parts fiche are present, so I'm thinking that at some point the drive housing may have taken a slight bow, but I don't have the brass to risk trying to press it a bit flatter, even with the possible bow the rear wheel spins freely.

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I have a new drive and am able to squeeze .085 worth of feeler gauges between the retainer and hub cover. Hopefully it stays that way when the axle gets tightened.

maylar said:

I have a new drive and am able to squeeze .085 worth of feeler gauges between the retainer and hub cover. Hopefully it stays that way when the axle gets tightened.

View attachment 16081

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There is no reason why it wouldn’t. The design is the axle tightens on the SPACER, nothing else. If the device was incorrectly assembled by a ham fisted lug somewhere along it’s life (not your NEW one of course, but generally speaking) then begins the failure.
Also, as shown in your picture, an .08 second visual inspection verifies shoulder to shoulder....
Mechanics 101. No disrespect intended to anyone, but, this topic blossoms into voodoo black magic, when it doesn’t need be.
JMWO

concours said:

The design is the axle tightens on the SPACER, nothing else.

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Which assumes that the spacer is exactly the correct length to prevent the gearbox from being crushed. With my (also new) spacer in place, there is zero space between its shoulder and the speedo drive. I would hope that there's only a couple thousandths of an inch between the spacer and wheel center, but I can't measure that.

Voodoo indeed...

L.A.B. said:

Not just lubricated but periodically cleaned otherwise the crud builds up to the point where it impedes the rotation of the ring gear.

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take note of LAB's statement. what I suspect caused my speedo-gearbox failure. note the small groove on the aft side of the ring gear. the groove is concentric, but not centered around the gearbox's axis. my WAG theory - grease is captured by the small groove, and through rotation and a simple, centrifugal force pumping action, is being constantly distributed between the ring gear and the gearbox housing. that area was the cause of my failure. when I disassembled my gearbox, it was noted that the ring groove was pretty much blocked with, what looked like, dried, burnt, caked, grease, impeding lubrication. even though I had grease in the assembly, I didn't have proper internal lubrication. friction built up thus causing the failure. so, my 2-cents, FWIW, and per LAB's comment, get in the groove - add removal and disassembly of the speedo-gearbox to the list of periodic maintenance items. I would say, if you have a bouncing speedo needle, especially at lower speeds, you may want to look into a full speedo-gearbox service.



pretty simple design with only a couple moving parts - easy rebuild. i'll be using dynodave's suggestion on using 2-56 flat heads to replace the original factory rivets. thanks dave, thanks LAB.