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

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this is the second time this happened. first time, I blamed it on a poorly constructed cable assembly, but it has hit me for a second time, so something's wrong here.

went out yesterday for a 70 mile run on the 74 - longest run to date since getting the bike back on the road. overall, the bike ran great, no issues until I got home and as I pulled the bike into the garage, I noticed this - it must have failed during the last mile or two since I don't recall not having any speedometer reading .

IMG-2472.jpg


IMG-2473.jpg


when I installed the speedometer cable(s), I thought I allowed for full swing arm travel, but it's obvious I didn't or there is some other factor at play here. ONE QUESTION I HAVE is whether the speedometer gearbox is supposed to pivot around the rear axle, thus allowing for swingarm travel, or is it supposed to be fixed and any swingarm movement is compensated by slack in the cable?

looks like I need to remove the speedometer gearbox for some sort of maintenance or service. could something be broken (internal to the speedo gearbox). new territory for me - not sure what to do at this point. looking for some guidance and input. TIA....
 

L.A.B.

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ONE QUESTION I HAVE is whether the speedometer gearbox is supposed to pivot around the rear axle, thus allowing for swingarm travel, or is it supposed to be fixed and any swingarm movement is compensated by slack in the cable?

Fixed.

The grease leakage is usually a symptom of the drive gearbox overheating due to the hub cover rubbing against it.
 
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The grease leakage is usually a symptom of the drive gearbox overheating due to the hub cover rubbing against it.
OK - and how do I fix this? I see there is a spacer (part 34, NM13270) - could that be the issue? I don't think I have any missing parts, and I did torque the axle to spec when I installed the cush hub buffers. the first cable failure was before I installed the cush buffers, so I don't think it has anything to do with this.

still not sure why the cable end failed - ???? that seems to be associated with swingarm movement or travel.
 
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L.A.B.

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OK - and how do I fix this? I see there is a spacer (part 34, NM13270) - could that be tieh issue? I don't think I have any missing parts, and I did torque the axle to spec when I installed the cush hub buffers. the first cable failure was before I installed the cush buffers, so I don't think it has anything to do with this.


https://www.accessnorton.com/NortonCommando/shim-on-speedometer-drive.26779/
https://www.accessnorton.com/NortonCommando/speedo-gearbox-problem.2359/
 
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one additional thing - (when in neutral) my rear wheel assembly does not seem to rotate freely. while it does turn, it seems something is binding and causing drag. maybe something else going on here. still don't understand why the cable end came "unglued" - ???
 
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L.A.B.

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one additional thing - (when in neutral) my rear wheel assembly does not seem to rotate freely. while it does turn, it seems something is binding and causing drag.

The hub cover rubbing, presumably?
Does the binding stop or reduce when the spindle/axle is slackened off?

still don't understand why the cable end came "unglued" - ???

I don't know. I'd guess the plastic sheathing could have softened enough from the heat for the ferrule crimp (which is normally crimped over the plastic sheathing) to lose its grip?
 
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The hub cover rubbing, presumably?
Does the binding stop or reduce when the spindle/axle is slackened off?



I don't know. I'd guess the plastic sheathing could have softened enough from the heat for the ferrule crimp (which is normally crimped over the plastic sheathing) to lose its grip?
i'll have to check if the binding eases up when I back off the spindle/axle. makes sense on the plastic sheathing and heat. just speculating, but it seems the cable assembly would have to have excessive tension in order to separate. grabbing at straws here....
 

L.A.B.

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i'll have to check if the binding eases up when I back off the spindle/axle. makes sense on the plastic sheathing and heat. just speculating, but it seems the cable assembly would have to have excessive tension in order to separate. grabbing at straws here....

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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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.
cable shown MAY be the original cable - can't say for sure, but same thing happened to a new venhill assembly previously. two cables has me a bit suspicious - then again, can't see how anything can be in tension.
 
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backed off the axle/spindle and the binding eased up significantly, so I leaning toward a spacer (#34) issue. did notice grease coming out from behind the rear hub cover --

IMG-2474.jpg


I think I need to disassembly everything for inspection, and identify the problem early on to get any parts on order. hopefully there is no issues with the speedo gearbox - doesn't appear to be a serviceable item. seems to be a little pricey.
 
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The top hat spacer that is outside the speedo drive should actually be inside the drive where it fits the gap between the axle and the wheel bearing. As installed the drive fouls the rear wheel hub cover and when tightened the drive distorts and fails. In this case I guess it spat out the drive cable. The workshop manual shows the spacer fitted the way you have it. It should be fitted into the bearing and then the speedo drive is fitted.
 

NPeteN

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^^HoveToo is correct. I had the same issue, it was the spacer, or rather lack of spacer. The exploded drawings are misleading.
 
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The top hat spacer that is outside the speedo drive should actually be inside the drive where it fits the gap between the axle and the wheel bearing. As installed the drive fouls the rear wheel hub cover and when tightened the drive distorts and fails. In this case I guess it spat out the drive cable. The workshop manual shows the spacer fitted the way you have it. It should be fitted into the bearing and then the speedo drive is fitted.
am I understanding you that the spacer is on the wrong side of speedo gearbox? not sure I have a clear understanding on how things are assembled - probably get a better picture of it when I start taking things apart.
 
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Another thing to check when you get the gearbox off, is to check that when you pump grease into the box that it actually gets in, The grease nipple/gun being of the 'push on' type doesn't have positive connection like the 'hydraulic' variety and the little spring loaded ball in the nipple itself takes quite some pressure to overcome. I remove the spring and ball so making routine greasing easier.
 

maylar

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The top hat spacer that is outside the speedo drive should actually be inside the drive where it fits the gap between the axle and the wheel bearing.

Then why do the exploded parts views for every year show it on the outside?
 

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Then why do the exploded parts views for every year show it on the outside?

The photo is misleading. It is only the cylindrical spacer between the swingarm and the gearbox body. The top hat fits inside the wheel bearing and inside the gearbox, sandwhiching the gearbox housing between the outside spacer and the top hat spacer on the inside.

Insert the top hat spacer into the wheel bearing, then place the gearbox over the lip of the spacer (brim of the top hat) this provides clearance for the wheel to spin without binding the gearbox.
 

L.A.B.

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am I understanding you that the spacer is on the wrong side of speedo gearbox? not sure I have a clear understanding on how things are assembled - probably get a better picture of it when I start taking things apart.

There has been some discussion about which side the top hat spacer belongs as it's usually found on the outside and as mentioned where it's drawn in the parts book diagrams.

Edit: Also, in the factory manual it states in 'Wheel Removal' section H3, 6: "Remove the right side spacer, washer and speedometer drive box."

Fig, H5 also shows the spacer outboard of the drive gearbox.
Tophatwasher.jpg
 
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maylar

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The top hat fits inside the wheel bearing and inside the gearbox, sandwhiching the gearbox housing between the outside spacer and the top hat spacer on the inside.

Again, that's clearly not how the parts lists show it. Where is it written (tech notes or service bulletin maybe) that the diagrams are wrong?

I'm in process of servicing my rear wheel right now and I discovered that the hub cover has been damaged by the speedo drive. I have a new drive and tophat spacer and will find out which way gives clearance.
 
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There has been some discussion about which side the top hat spacer belongs as it's usually found on the outside and as mentioned where it's drawn in the parts book diagrams.
still don't have a clear understanding of how things are assembled. i would think it only goes together one way, however if not obvious, would think one way would fit better than the other - ????
 
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