Speedo Gearbox

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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thornebt
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Speedo Gearbox

Post by thornebt »

I know this subject has been covered many times on this forum but I have a very simple question. Does it matter if the hole reamed out in the centre of the speedo gearbox is a tight fit? I had to tap my speedo gearbox on some time ago and it was fine until recently when it seemed to twist and detatch the cable. As I understand it a tight fit should be fine as the axle doesn't turn.

Also, I think I remember reading that it's important to tighten the axle before tightening up the speedo gearbox nut. If that's correct that might be where I went wrong last time I had the wheel out. That could be the cause of my problem.

Cheers. Bruce.
Mick D
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Re: Speedo Gearbox

Post by Mick D »

Hi

It will not matter if the gearbox case is a tight fit as the threaded collar which retains the gearbox does not rotate with the wheel, however in order to tighten the speedo gearbox retaining nut the collar must be held fast, this is achieved by tightening the wheel spindle first.

Regards Mick
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thornebt
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Re: Speedo Gearbox

Post by thornebt »

Thanks Mick. That all makes sense. Do you think it would be good practice when removing the wheel with the speedo gearbox attached to then loosen the speedo gearbox before tightening the wheel spindle? Perhaps my problem was caused by me tightening the spindle more than the previous time and this affected the speedo gearbox causing it to bind or whatever.

Cheers. Bruce.
Mick D
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Re: Speedo Gearbox

Post by Mick D »

Hi Bruce

You shouldn't need to loosen the gearbox nut, the position of the gearbox is set by the flange on the collar, just hold the gearbox in the correct orientation as you tighten the wheel spindle, (ensuring the two drive dogs are correctly engaged first ;) ). Once the wheel spindle is tight it's always good practice to confirm the gearbox retaining nut is secure.
Speedo Flange.png
Regards Mick
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Rob Harknett
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Re: Speedo Gearbox

Post by Rob Harknett »

The same applies in reverse, you cannot undo the speedo box nut with the wheel not tightened in the machine. EG tighten or lossen speedo drive nut only with the wheel fully fitted. ( axel nut tight, you can see in pic the part that hold the speed takes just nut nut, the other end cannot be held. Only pressure by having the axel nut tight, will allow the speed drive nut to be undone or tightened.)
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thornebt
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Re: Speedo Gearbox

Post by thornebt »

Thank you very much Mick and Rob. The job is now done. I've greased the wheel bearings at the same time. There is still a major sqeak when I spin the wheel but perhaps there always was. I've got a small amount of play at the rim so they can't be too tight. The speedo gearbox is secure and seems to be behaving itself. There's a tad less paint on it than when I started but the main thing is that it works. Test drive tomorrow maybe.

Cheers. Bruce.
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Rob Harknett
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Re: Speedo Gearbox

Post by Rob Harknett »

You should not hear a squeak, some bearing rumble perhaps. Squeak may be brake binding?
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clive
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Re: Speedo Gearbox

Post by clive »

Which sort of speedo box do you have? One possible reason for the drivebox rotating is if the worm drive is badly worn, if so the worm and its drive gear can cross and snag momentarily. This will then cause the drivebox to rotate regardless of how tight the retaining nut is. If you have the drivebox with the flat end I would be inclined to turn it off and check how worn the worm drive is, especially as you have a squeak. If you have the torpedo type its less easy to get off without removing it from the bike. Its vital to regrease the drive every thousand miles as per the owners books to keep wear to a minimum.
clive
if it ain't broke don't fix
Mick D
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Re: Speedo Gearbox

Post by Mick D »

Hi Bruce

I'd be a little concerned regarding the squeak, it's indicative of a dry rubbing surface. As you've greased the wheel bearings they can be discounted.
Re Rob's suggestion of the rear brake - wind off the brake adjuster until it no longer acts on the lever and spin the wheel, is the noise still present? If not, it's probably the brake shoes, did you check the brake rigging after you replaced the wheel? - the natural thing to do is to set the chain tension correctly, but that also requires the brake rigging to be checked / corrected.
If it's still there I'd be suspicious of the gearbox suffering damage, whack a bit of grease in if yours has a nipple and see what effect that has, or take off the gearbox and inspect it for damage.

All easy stuff and should be achievable before the weekend.

Regards Mick
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thornebt
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Re: Speedo Gearbox

Post by thornebt »

Top diagnosis, thank you. I backed off the rear brake until the squeak disappeared. This gives about 2" of movement at the front of the brake pedal which might sound excessive but doesn't look too bad in real life.

I also found that the large nut that tightens up the brake side of the hub was loose (QD wheel). I suspect that this was giving me the slight rock in the wheel rim and that I have probably overtightened the bearings. So I've backed off the wheel bearing adjuster and will take it round a few corners tomorrow to free them up slightly and adjust until I get a very slight amount of play at the rim.

Thanks again for your help.

Cheers. Bruce.
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