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

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joe czech said:
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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The top hat spacer can go inside and if it works better that way then it's up to you as I'm not saying it must go on the outside.
 
maylar said:
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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Hey, I get your resistance to stray from the parts list.

I'm just saying, I had the exact same issue and resolved it by placing the top hat on the inside. If you search on the forum there are several threads that present the same solution as well.

I hope whatever solution you find gets you back on the road fast!

I will also add that I believe the drawing to be misleading because on my bike, having never had the rear wheel off (original tires) the top hat was inside the wheel bearing.

This is a photo of the setup after 40 years in a storage closet, original tires etc... You can see that the cylindrical spacer, and ONLY the spacer is in contact with the outside of the gearbox drive. This is a 1970, so perhaps different than yours.
speedometer gearbox/cable -- what's wrong and how do i fix it?
 
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The speedo drive box can become distorted or dished if the top hat gets crushed from axle torque. That can lead to worm gear interference, over heating and the infamous Black Star of Death hot grease spread over the hub cover. The box can be tapped back to reasonable shape on the bench as it is relatively soft.
Its problems like this that lead folks to speedo alternatives (gps or magnetic. Pick up types).
 
with the top hat moved to the inside the hole in the drive is a VERY loose fit on the axle so you run the risk of it being off center. that is why it is installed from the outside.
 
got into the hub/speedo gearbox - have a couple questions. I found this thing somewhere around the lock ring. looks to be part of something, dumb old me, pulled it out before engaging my brain. not sure if it's part of the speedo gearbox or what - ???

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


second, are the speedo gearboxes serviceable. mine has the inner ring that engages the lock ring. the inner ring has this grinding sound, and seems to be binding up internally. the parts list diagram does not show individual components, so i'm assuming it may be a "lowest replaceable unit" part, and non-serviceable - unless I'm missing something, I don't see any easy means of disassembly.

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


as for the top hat spacer, it seems that part of it's function is to keep the speedo gearbox from distorting when torqueing the axle shaft. the sppedo gearbox looks like it's a zinc-aluminum alloy. torqueing the axle shaft against the spacer against the speedo gearbox housing, i'm thinking, may distort the housing. just speculating....
 
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Tornado said:
The speedo drive box can become distorted or dished if the top hat gets crushed from axle torque. That can lead to worm gear interference, over heating and the infamous Black Star of Death hot grease spread over the hub cover. The box can be tapped back to reasonable shape on the bench as it is relatively soft.
Its problems like this that lead folks to speedo alternatives (gps or magnetic. Pick up types).
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black star of death grease - now I get it! that's some pretty nasty stuff!!!
 
joe czech said:
got into the hub/speedo gearbox - have a couple questions. I found this thing somewhere around the lock ring. looks to be part of something, dumb old me, pulled it out before engaging my brain. not sure if it's part of the speedo gearbox or what - ???

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


second, are the speedo gearboxes serviceable. mine has the inner ring that engages the lock ring. the inner ring has this grinding sound, and seems to be binding up internally. the parts list diagram does not show individual components, so i'm assuming it may be a "lowest replaceable unit" part, and non-serviceable - unless I'm missing something, I don't see any easy means of disassembly.

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


as for the top hat spacer, it seems that part of it's function is to keep the speedo gearbox from distorting when torqueing the axle shaft. the sppedo gearbox looks like it's a zinc-aluminum alloy. torqueing the axle shaft against the spacer against the speedo gearbox housing, i'm thinking, may distort the housing. just speculating....
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It can and will distort. Mine was dished in and I was able to re-flatten with careful use of bench vice and some bits of wood. There are some threads on the forum where folks have disassembled them and managed to recover some function, but they are poorly made for the job they try to do. There are original and re-pop speedos on the market. Really needs someone to redsign or improve the materials the gearing is made of....but seems a difficult machining operation on the worm & ring gears. I guess the biggest issue is the way the spacers fit on the Norton....leading the crushed housing. Have not heard these units failing so much on other bikes.
 
Many years ago when doing my rolling restoration , the speedo drive just died no apparent cause from what I could see .... didn’t even try to rebuild , ordered new one along with cable and having Speedo rebuilt by Dave Saurberg (RIP) in western Canada .... worked perfect till last year when cable end failed (my fault) got replacement cable from ”Vintage Brit Cables” out in western Canada (they are Dave’s old business) they work from the original drawings and supply very high quality , heavy duty pieces , very pleased with prices and service .... plus a bargain for Americans to shop in Canada these days .....
 
update -- not sure if my speedo gearbox assembly is rebuildable. seems the guide ring machined into the housing (that keeps the ring gear located) is pretty much gone. that most likely is the root cause of the failure. I seem to have had a slight radial movement of the ring gear within the housing when it went took a dump. anyway, order's in to old britts for a replacement.

speedometer gearbox/cable -- what's wrong and how do i fix it?
 
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Craig said:
Many years ago when doing my rolling restoration , the speedo drive just died no apparent cause from what I could see .... didn’t even try to rebuild , ordered new one along with cable and having Speedo rebuilt by Dave Saurberg (RIP) in western Canada .... worked perfect till last year when cable end failed (my fault) got replacement cable from ”Vintage Brit Cables” out in western Canada (they are Dave’s old business) they work from the original drawings and supply very high quality , heavy duty pieces , very pleased with prices and service .... plus a bargain for Americans to shop in Canada these days .....
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any chance of posting contact info - address, phone number, web address - ???
 
joe czech said:
just visited the site - nice stuff. definitely like the double crimp configuration. will give them a try. thanks for the link!
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They do look great, shielding is spot on as well. But don't thank me, thank Possm post#32
 
Sorry Joe ! Thanks Pete , was kinda busy in shed and had left phone on kitchen table , in hindsight I should have just posted link in my post , will do better ... think the Lady is Joani ?
 
Craig said:
Sorry Joe ! Thanks Pete , was kinda busy in shed and had left phone on kitchen table , in hindsight I should have just posted link in my post , will do better ... think the Lady is Joani ?
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Good memory Craig, spoke with her earlier today. Nice lady
 
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