Topic: Speedo not working.

[juntjoo]

Once this little gearbox down here stops turning is it done? It's not moving at all.

[70CB750]

Yes, if you spin the wheel, it should turn.  I would take it off the wheel to have a closer look. 

[juntjoo]

Yes, if you spin the wheel, it should turn.  I would take it off the wheel to have a closer look.

Well it's definitely not. I'll check it out later. If it's working properly it should also not turn while the wheel remains stationary too correct? I think I was able to turn in as if it's not locked to the wheel. Can it be serviced? After I take it off will it come apart? Never seen these.

[Alan F.]

#8 turns with the wheel, #10 engages to #8 and is turned by the wheel. Your speedometer cable fits into #10 to bring this rotation up to your speedometer.

#10 is referred to as Speedometer drive, Speedo gearbox, etc. It has 2 gears inside that must mesh. Some can be disassembled and cleaned, some must be cleaned while assembled, its a messy job. Then new grease must be packed around the gears before reinstalling.

A clean, lubricated, and unbroken speedometer cable is required. Speedometer cables get dirty inside and need to be flushed out and re-lubricated eventually. They can also break internally. It's easy to spot a broken speedometer cable, disconnect the cable at both ends and pull out the interior part of the cable with a pair of pliers. It should be the full length of the Outer part of the cable when removed. If it's shorter, you've found a broken speedometer cable, you'll need a new one.

[juntjoo]

There should be a notch or tab on your speedometer gearbox that fits to a tab or protrusion on your fork lower to keep the gearbox from spinning independently.

From your photo it looks like these tabs are not lined up. It seems the last person to assemble that wheel to those forks didn't assemble properly. It's going to have to come apart for inspection before you can determine what's causing the issue.

I'm not sure what you're talking about but I think you're referring to a different design with mine (82 cb650sc) is different in many ways apparently, but the way I have it as pictured is turned up to access it. I just loosened the axle a bit to do that to inspect it. My cable is new as the old one broke. And now it again stopped working but I narrowed it down to this gear assembly. I thought I read somewhere in here about the gears wearing out or something. Thanks. Okay, I'll have to take it out and inspect it. Can I leave it out and still ride it? I'll find out

[Bodi]

There's a spiral gear on the part driven by the hub and another gear on the output shaft that mates to it. Personally I haven't seen those gears wear out but they could.
The individual parts were never available from Honda, only the complete (NLA) assembly. The tiny oil seal on the output shaft is - for me, at least - pure unobtanium. The seal for the big driven gear is not hard to find.
Removing the drive unit should let you see exactly what went wrong. It is a vital spacer in the axle stack- you need it or some sort of other spacer there to use the bike. A stack of washers will work in a pinch if you can find a suitable size.
Some drives may have a tab or something to lock the drive from locating but I have never noticed that on a SOHC4. Common for locking the drum front brake plates to a fork leg on smaller bikes tough. It is kept from turning just by axle nut tension.
Did you have the wheel out, service the bearings? The drive parts are somewhat hard to understand, and it is possible to omit or misassemble parts.

[juntjoo]

There's a spiral gear on the part driven by the hub and another gear on the output shaft that mates to it. Personally I haven't seen those gears wear out but they could.
The individual parts were never available from Honda, only the complete (NLA) assembly. The tiny oil seal on the output shaft is - for me, at least - pure unobtanium. The seal for the big driven gear is not hard to find.
Removing the drive unit should let you see exactly what went wrong. It is a vital spacer in the axle stack- you need it or some sort of other spacer there to use the bike. A stack of washers will work in a pinch if you can find a suitable size.
Some drives may have a tab or something to lock the drive from locating but I have never noticed that on a SOHC4. Common for locking the drum front brake plates to a fork leg on smaller bikes tough. It is kept from turning just by axle nut tension.
Did you have the wheel out, service the bearings? The drive parts are somewhat hard to understand, and it is possible to omit or misassemble parts.

Thanks for all that info. Sounds like you been in there. I haven't, no. But I'll have your response on hand for when I do. Maybe I'll grab some washers as you suggested before I do take it apart in case it will take a while. Will update later. Sounds fun. Lol, not really

[Bodi]

For washers, the one against the hub bearing must contact only the inner race, not the outer race at all. I don't recommend washers as you need a pretty specific size to not ruin the seal and to contact the bearing properly. Diagnosing the problem and deciding whether you can fix it or it needs replacement should only take a few minutes. Either way you can just put it back in and ride with no speedo for a while.

[754]

If it is broken but still turns, it' can be the spacer.. just  remove  1 gear.
 
Yeah washers, you be all day , grinding off outside , or opening up the hole if you have no lathe. .

[BenelliSEI]

If it’s the same as 1972-78 CB750 I have a box full of them. Will send you one for postage. Post pictures if you remove it check it.......

[754]

You can see it in the pic, looks different ..

[BenelliSEI]

You can see it in the pic, looks different ..

True..... ignore my previous post!

[Alan F.]

Not sure how this isn't appearing in my first post...

[70CB750]

If it’s the same as 1972-78 CB750 I have a box full of them. Will send you one for postage. Post pictures if you remove it check it.......

It looks the same as speedo on my 1982 CB900C.  I would not be surprised if Honda used the same on his bike, same year and all that.   I am sure there are plenty on ebay.

See pictures, Nighthawk is the black one, logically  

[Scott S]

 That gear fit 185 different models. Wouldn't be hard to find a replacement.

 It might not turn if the axle is loose. The gears on the drive (#8 in Alan's pic) must engage the drive properly.

 Not way I'd try to repair one or rig up something. Just find a replacement. If you know how to search Partzilla, it will tell you what models it was used on. Then search Ebay for those models, or even the Honda part number, which is 44800-425-013, BTW.

[juntjoo]

That gear fit 185 different models. Wouldn't be hard to find a replacement.

 It might not turn if the axle is loose. The gears on the drive (#8 in Alan's pic) must engage the drive properly.

 Not way I'd try to repair one or rig up something. Just find a replacement. If you know how to search Partzilla, it will tell you what models it was used on. Then search Ebay for those models, or even the Honda part number, which is 44800-425-013, BTW.

Good idea. Partzilla. I'll remember that. If you search your model you might not find the available ones listed for other compatible models.

Axle wasn't loose but I tested it with a alligator clip attached to that little tooth in there after I loosened the axle to turn it upwards, unnecessarily. Probably won't matter but I'll put it in its default downward position and test again...and grab a replacement if needed.

[Scott S]

 You need to have a log in for Partzilla. If you do that, you can find the part for your model, then click "where used" or something like that.  It will show you a list of all the bikes it was used on.
 

[70CB750]

You need to have a log in for Partzilla. If you do that, you can find the part for your model, then click "where used" or something like that.  It will show you a list of all the bikes it was used on.

I did not know that, neat trick.

[Alan F.]

Same with cmsnl.

One tip is that Honda had different drive ratios at the front wheel for different size front wheels. When swapping parts for custom setups we just choose the correct speedo drive to match. That's how Honda got away with using the same speedometer rotations:speed ratio on so many different bikes.