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speedo gearbox?


Well Known and Active Forum Website User
Non-VOC Member
Hi all, I have still only ridden my Comet once but am getting nearer to registration, I just remembered that when I rode it that there was quite a bit of noise from the speedo gearbox (or more likely from the meshing of the H23 speedo gear ring and the gearbox) my question is: are they normally noisy, if not has anyone had this problem before? I have tried many things to quieten it but to no avail.



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VOC Member
Kevin, they are not normally noisy. There is adjustment in and out of the gearbox to allow it to line up perfectly with the H23. I have seen H23s where the bike has been run for year with an incorrect mesh and the H23 has been worn out for half or more of its width and the remainder of the teeth badly distorted. As you have just done a rebuild then you would have noticed this fault, assuming that you had the brake apart. Does the input cog to the gearbox rotate freely by hand with everything above the gearbox still connected? If not look at the cable and speedo. If it does, then look at the teeth on the gearbox pinion and the H23. They should be a nice fit into each other. If that seems ok then spin the wheel without the speedo gearbox to ensure that the noise is not a wheel bearing or something else. If the wheel spins without noise and the speedo gearbox does the same then is there any possibility that the centre of the hole etc for the gearox is in the wrong place meaning that the teeth would be either too tight or too loose in mesh. If everything looks ok then I would spin the front wheel without the gearbox and then insert the box etc while the wheel is still spinning and get a manual feel as to where the roughness is occurring. Good luck.

Pete Appleton

VOC Hon. Editor
VOC Member
VOC Forum Website Administrator
Hello Kevin
My newly rebuilt 'A' had the same problem. A shiny round mark on the side of the brake shoe, visible through the drive hole in the backplate, showed that I had got the penetration adjustment wrong as refered to by T.T above. I wouldn't have believed it possible for it to have made as much noise as it did.



Active Forum Website User
Non-VOC Member
When i replaced this cog it had worn three steps into the gear from being readjusted as many times over many years. Picture 017.jpg

Ken Tidswell

Well Known and Active Forum Website User
VOC Member
A high frequency scream form the front may be a dry gearbox. Corrosion between the shaft and the body causes the
body to produce oxide which binds the shaft which drives the speedo.
It is a good idea to disassemble the right angle drive clean out all the old grease and make sure the shafts run freely in the various housings regrease and reassemble, taking care to stake the part with the grease nipple in it. You might find that applying the grease gun forces out the plate due to the hydraulic pressure of the grease. Ken


Well Known and Active Forum Website User
VOC Member
The speedo gearbox on my Comet was so worn that I had to make a jig so that i could bore the body out and fit a bush in it.
It is also worth fitting a nylon gear instead of a steel one.
I have also seen a 2 piece mounting plate made that has a loose,eccentric threaded section.This allowed for adjustment of the gear engagement. After seeing it I made one for my 1932 Sunbeam as I could not get the gears to assemble any other way..John


Well Known and Active Forum Website User
VOC Member
I have metal to metal gears and they are whisper quiet with correct adjustment. Check the gearbox: old hard grease can cause a lot of problems. Check the end float on the gearbox input shaft; too much end float will have the gears riding over each other, putting stress on the end cap which will pop out and the gear drive will soon follow it. Check the split pin securing the gear isn't rubbing against anything, I found a little pile of brass inside one of my front wheels due to this. If your speedo gearbox needs re-building then Tim Thearle in Orange is you go-to man.
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