speedo cable routing

joe czech · Jul 7, 2020

texasSlick said:
It is common for Speedo drives to deform with the center bulging outboard. Why this happens, I do not know. It happened to my original Speedo drive, and I do know that I never over torgued the axle.

When the drive bulges outboard, it causes the inner surface of the drive to move nearer, and possibly rub on the cover of the wheel hub (that polished thin metal cover with the three plugs for the bolt up wheels). In my case, the cover was gouged to destruction.

Bulged Speedo drives can be salvaged. Warm the pot metal and squeeze it with a vise, using a socket of proper diameter to press on the center. The thickness of a speedo drive should be approx. 0.80 inches without any top hat bushing.

View attachment 17477

Slick

just checked my failed original, and if measuring correctly, i'm at .845

I think i'm beginning to understand this - it looks like if you're at the .800 dimension, the internal ring gear is now, more in-line with the input pinion drive gear. I think you need a perfect mesh between the two gears. if you're greater than the .800 mark, it seems the ring gear is now shifted and allows contact with the internal surface of the housing, thus causing rubbing and binding. by eliminating that housing "bulge," it shifts the ring gear more to the center line of the pinion gear, and should eliminate the binding.

going to disassemble my original, take some measurements to see if the .800 mark does indeed position the ring gear to eliminate the binding and position it more in-line with the drive pinion gear. I think i'm seeing why my original at .845" is still binding after rebuild. would really like to salvage this thing. thanks for the information Slick -

maylar · Jul 7, 2020

joe czech said:
on the axle shaft - it would have to be at least grade 5 - anything less would be in the soft metal range. if torque value (9/16-fine, grade 5 @ mid-range yield) is 91 ft,lbs. - if less than 70% or 63 ft.lbs., i'd feel safer using a (blue) thread locker. only saying this because mylar's "calibrated elbow" torqued the shaft to around 50.

I'm using a stainless axle, don't know what alloy or hardness. I'm tempted to use anti seize rather than Loctite.

Consider that the factory didn't specify a torque spec and that the original tool kit included a stamped steel box spanner that could be used for adjusting chain tension or removing the wheel for fixing a flat (I've done both on the road). No way in hell you could come close to 80 ft lb with that, even smacking it with a rock. I'll double check what my calibrated elbow put it at, but I'm inclined to take Dave's advice and shoot for 40-50 ft lbs. Never had an axle come loose, but I have crushed speedo drives.

joe czech · Jul 7, 2020

maylar said:
I'm using a stainless axle, don't know what alloy or hardness. I'm tempted to use anti seize rather than Loctite.

Consider that the factory didn't specify a torque spec and that the original tool kit included a stamped steel box spanner that could be used for adjusting chain tension or removing the wheel for fixing a flat (I've done both on the road). No way in hell you could come close to 80 ft lb with that, even smacking it with a rock. I'll double check what my calibrated elbow put it at, but I'm inclined to take Dave's advice and shoot for 40-50 ft lbs. Never had an axle come loose, but I have crushed speedo drives.

I've seen several sites, old brits, andover-norton, to name a few - all spec'd 80. don't think anyone pulled that number out of their butt. makes sense to me since most designers typically set (critical) torque values to 80-90% yield. 80 puts the axle shaft at 89%, so from a reverse engineering standpoint and if 80 is a good number, the Norton folks hit the nail on the head. however, 40-50 or whatever works for you is OK with me - just throwing out my 2-cents (FWIW) and a few suggestions. on the stainless axle shaft, i'm thinking unless you're going stainless to stainless, you shouldn't need anti-seize, but then again, applying it won't hurt anything. just remember, anti-seize is a lubricant, and it will affect torque values. as for the axle backing off, I would think the chain adjustment bolt assembly does double duty by providing a locking mechanism to the shaft.

side note - slowly changing over to stainless on my 74 - where did you get the stainless axle shaft?

peace

texasSlick · Jul 7, 2020

joe czech said " side note - slowly changing over to stainless on my 74 - where did you get the stainless axle shaft? "

Madass140 makes them. He is on this Forum. Use the search function.

Slick

olympus · Jul 7, 2020

RGM also sell stainless shafts & nuts

maylar · Jul 7, 2020

joe czech said:
side note - slowly changing over to stainless on my 74 - where did you get the stainless axle shaft?

eBay -

https://www.ebay.com/itm/Norton-Com...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

NickZ · Jul 7, 2020

joe czech said:
just checked my failed original, and if measuring correctly, i'm at .845

I think i'm beginning to understand this - it looks like if you're at the .800 dimension, the internal ring gear is now, more in-line with the input pinion drive gear. I think you need a perfect mesh between the two gears. if you're greater than the .800 mark, it seems the ring gear is now shifted and allows contact with the internal surface of the housing, thus causing rubbing and binding. by eliminating that housing "bulge," it shifts the ring gear more to the center line of the pinion gear, and should eliminate the binding.

going to disassemble my original, take some measurements to see if the .800 mark does indeed position the ring gear to eliminate the binding and position it more in-line with the drive pinion gear. I think i'm seeing why my original at .845" is still binding after rebuild. would really like to salvage this thing. thanks for the information Slick -

My housing was bulged to around 0.9. I used Slick's method and brought it back to 0.8". That made a definite, noticeable difference in the smoothness of the gears meshing. Ring turned easily, with none of the binding I felt before the fix.

By the way, an inner race from a steering head bearing was the best fit I found for use on the outside of the housing for straightening in a vice. I put a 15/16" socket between that and the vice jaw, with plywood between the other jaw and the housing. Don't forget the heat.

joe czech · Jul 7, 2020

NickZ said:
My housing was bulged to around 0.9. I used Slick's method and brought it back to 0.8". That made a definite, noticeable difference in the smoothness of the gears meshing. Ring turned easily, with none of the binding I felt before the fix.

By the way, an inner race from a steering head bearing was the best fit I found for use on the outside of the housing for straightening in a vice. I put a 15/16" socket between that and the vice jaw, with plywood between the other jaw and the housing. Don't forget the heat.

OK, Slick says to "warm the pot metal" - need more details. off the top of my head, i'm thinking boiling water should suffice - yes, no, ???

NickZ · Jul 7, 2020

joe czech said:
OK, Slick says to "warm the pot metal" - need more details. off the top of my head, i'm thinking boiling water should suffice - yes, no, ???

I used a heat gun, but boiling water should work too.

texasSlick · Jul 8, 2020

Update re: salvaging speedo gearbox after bulging:

I received a PM from a Forum member to elaborate on salvaging a bulged gearbox. For the benefit of all, I am including my answer here.

Warming the gearbox: My engineering "guts" says 350 - 400 F (175 - 200 C) should be adequate. One could use the kitchen oven if momma isn't home. I played a propane torch on the center part (which needs to yield to move the bulge) for about 20 seconds. A heat gun might require more time ... depends on the gun ... use your own discretion.

The 0.8 dimension is not any specification. I once saw a web page with the thickness value when I was searching for replacement parts (none available), but since then, I have not been able to find it again. That number sticks in my head, and IIRC, it was the value that resulted when I squeezed my box down.

As an engineer, I would think the over-riding factor in squeezing down the bulge, is to bring the center part of the housing (where the top hat fits) flush with the outer perimeter of the box. In other words, a straight edge laid across the diameter of the gearbox, should equally contact the perimeter ring, and the top hat surface. Of course, the top hat bushing should not be present when doing this. I arrive at this conclusion, because I see no reason why the designer of the housing would intentionally make the center protrude or be recessed from the main body.

HTH

Slick

BTW ... Classic Bike Spares lists EMGO knockoff speedo gearboxes. They claim quality and service life to be "comparable to Smith's". FWIW

joe czech · Jul 8, 2020

texasSlick said:
Update re: salvaging speedo gearbox after bulging:

I received a PM from a Forum member to elaborate on salvaging a bulged gearbox. For the benefit of all, I am including my answer here.

Warming the gearbox: My engineering "guts" says 350 - 400 F (175 - 200 C) should be adequate. One could use the kitchen oven if momma isn't home. I played a propane torch on the center part (which needs to yield to move the bulge) for about 20 seconds. A heat gun might require more time ... depends on the gun ... use your own discretion.

The 0.8 dimension is not any specification. I once saw a web page with the thickness value when I was searching for replacement parts (none available), but since then, I have not been able to find it again. That number sticks in my head, and IIRC, it was the value that resulted when I squeezed my box down.

As an engineer, I would think the over-riding factor in squeezing down the bulge, is to bring the center part of the housing (where the top hat fits) flush with the outer perimeter of the box. In other words, a straight edge laid across the diameter of the gearbox, should equally contact the perimeter ring, and the top hat surface. Of course, the top hat bushing should not be present when doing this. I arrive at this conclusion, because I see no reason why the designer of the housing would intentionally make the center protrude or be recessed from the main body.

HTH

Slick

BTW ... Classic Bike Spares lists EMGO knockoff speedo gearboxes. They claim quality and service life to be "comparable to Smith's". FWIW

thanks Slick - i'm thinking the ideal dimension of the housing should be when the two gears are in a near perfect (center line) mesh. one could work backwards to calculate the dimension of the housing and bulge elimination based on the measurement of internal components. my housing is sitting here and that's the route i'll be taking - i'll get to it sometime down the road and post my results. again, thanks for the input.

HoveToo · Jul 8, 2020

Anyone read the other threads about the problem of deformed speedo drives?
My top hat spacer fits into the wheel bearing directly and sits between the speedo drive and hub cover. In that location you do not distort the speedo drive but you do fit the axle to the wheel bearing which I think is what it was there for. It was fitted in this way on my bike bought new in 1975. Yes the diagram shows different - it is incorrect. Many others have discussed this and prefer to fit the top hat through the speedo drive per the diagram. They all have scored hub covers and damaged speedo drives.

NPeteN · Jul 8, 2020

HoveToo said:
Anyone read the other threads about the problem of deformed speedo drives?
My top hat spacer fits into the wheel bearing directly and sits between the speedo drive and hub cover. In that location you do not distort the speedo drive but you do fit the axle to the wheel bearing which I think is what it was there for. It was fitted in this way on my bike bought new in 1975. Yes the diagram shows different - it is incorrect. Many others have discussed this and prefer to fit the top hat through the speedo drive per the diagram. They all have scored hub covers and damaged speedo drives.

This is exactly how mine came to me and I've never had an issue with all original parts. Some folks won't venture from the diagrams.

acadian · Jul 8, 2020

HoveToo said:
Anyone read the other threads about the problem of deformed speedo drives?
My top hat spacer fits into the wheel bearing directly and sits between the speedo drive and hub cover. In that location you do not distort the speedo drive but you do fit the axle to the wheel bearing which I think is what it was there for. It was fitted in this way on my bike bought new in 1975. Yes the diagram shows different - it is incorrect. Many others have discussed this and prefer to fit the top hat through the speedo drive per the diagram. They all have scored hub covers and damaged speedo drives.

I've never heard of this until now... learn something new every (other) day

NPeteN · Jul 8, 2020

Spacer outside, top hat inside.
This is my hub, untouched 40 years. Original tire.

NickZ · Jul 8, 2020

If the 06-7629 top hat spacer is inside the housing, what is its function? Other than the 0.060" thickness of its flange, it would seem redundant with 06-7704 (also sometimes referred to as a "top hat" spacer) which it would be in contact with.

texasSlick · Jul 8, 2020

NickZ said:
If the 06-7629 top hat spacer is inside the housing, what is its function? Other than the 0.060" thickness of its flange, it would seem redundant with 06-7704 (also sometimes referred to as a "top hat" spacer) which it would be in contact with.

I suppose the top hat spacer is for the purpose of allowing one or two "universal" gearboxes to fit dozens of bikes .... Smith's makes a few universal gearboxes and the bike mfgr makes one work by his own spacer. The spacer adapts Smith's central hole to the mfgr's axle diameter, as well as providing necessary clearances.

I have never heard of the spacer fitted inside the gearbox (that does not mean it never happened). I am the original owner of my Atlas, and I can testify the spacer was factory fitted from the outside.

If I were to swap the spacer to the inside, there would be nothing to center the gearbox on the axle, except perhaps, the drive dogs. I would not be comfortable with that arrangement.

Slick

NickZ · Jul 8, 2020

texasSlick said:
I suppose the top hat spacer is for the purpose of allowing one or two "universal" gearboxes to fit dozens of bikes .... Smith's makes a few universal gearboxes and the bike mfgr makes one work by his own spacer. The spacer adapts Smith's central hole to the mfgr's axle diameter, as well as providing necessary clearances.

I have never heard of the spacer fitted inside the gearbox (that does not mean it never happened). I am the original owner of my Atlas, and I can testify the spacer was factory fitted from the outside.

If I were to swap the spacer to the inside, there would be nothing to center the gearbox on the axle, except perhaps, the drive dogs. I would not be comfortable with that arrangement.

Slick

Right. That was my point. If the top hat is outside the housing, it performs the function of centering on the axel. If it is on the inside, I don't know what function it performs. Why would it need to be there?

HoveToo · Jul 9, 2020

I have the original top hat and wheel bearings to hand. The bearing ID is 0.675", the top hat OD is 0.675", the top hat ID is 0.58" ish. The Top Hat spacer wall thickness is about 0.04", *2 is 0.08" so you have that much free space between the axle and the wheel bearing without the spacer.

The TH spacer is 0.3" deep and the speedo drive is about .835" deep so fitting it outside does not reach the bearing. The purpose of the TH spacer is to engage the axle and wheel bearing. The flange also holds the speedo drive off the hub and prevents distortion of the drive when the axle is tightened.

Drawings can be inaccurate or drawn for convenience. Have a look at the drawing of the oil filter worm drive clamp.

joe czech · Jul 9, 2020

texasSlick said:
I suppose the top hat spacer is for the purpose of allowing one or two "universal" gearboxes to fit dozens of bikes .... Smith's makes a few universal gearboxes and the bike mfgr makes one work by his own spacer. The spacer adapts Smith's central hole to the mfgr's axle diameter, as well as providing necessary clearances.

I have never heard of the spacer fitted inside the gearbox (that does not mean it never happened). I am the original owner of my Atlas, and I can testify the spacer was factory fitted from the outside.

If I were to swap the spacer to the inside, there would be nothing to center the gearbox on the axle, except perhaps, the drive dogs. I would not be comfortable with that arrangement.

Slick

don't want to ruffle anyone's feathers, but have to agree with Slick on this one. on my 74, although I am not the original owner, my speedo-drive mechanism appears to be configured from the factory with the spacer installed from the outside. when the assembly failed and I proceeded to disassemble the unit, I had to press the spacer out as it seemed to be an interference or friction fit in place. i'm assuming from where the sleeve of the spacer may have "bulged" a bit during the torqueing application. don't know if all housings are similar, but after removing the spacer, the inner surface of the housing had a edge lip formed, i'm assuming, from the factory where the housing was designed for a one-way assembly. if it were designed to be installed from the inside, the inner surface would be flush to mate with the top-hat flange.

peace....

speedo cable routing

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