The Dreaded Speedo Gearbox

[Pharisee]

Happened to my M18S not long after I bought it. In my case, it was down to bad assembly by the previous owner that 'restored' the bike. The thread in the hub for the bearing adjusting ring was damaged and the ring wouldn't screw in far enough. The PO bolted it all together anyway, leaving the ring too far out, which distorted the drive gearbox, eventually causing it to jam completely.
I bought a new gearbox, adjusting ring and locking ring. It took some time to carefully clean up the hub thread so that the adjusting ring fitted correctly. It's been working perfectly ever since.

[bob121]

All back together. Salvaged about half of the threads in the hub. Drilled and helicoiled the hub to take a locking pin. Fitted the new speedo drive. Interestingly when tightening the lock nut the drive clamped onto the adjusting ring. I had to fit a a washer between the drive and the spacer/mount. The difference between two new drives is not to be ignored. Anyway, 45 miles and everything seems fine so far. I'll keep doing the local runs until I'm confident it's ok. Then back to doing some distance riding.

[Dibnah]

I'm aware of two AMC bikes that have suffered the speedo gearbox issue; the level of destruction and subsequent repairs required was an eye-opener.

A "bolt-on" anti-rotational device would be a useful precaution.

[Plugsnpoints]

I'm aware of two AMC bikes that have suffered the speedo gearbox issue; the level of destruction and subsequent repairs required was an eye-opener.

A "bolt-on" anti-rotational device would be a useful precaution.

Maybe there's an opportunity for an enterprising engineer to make a failsafe modification. I realise it won't be cheap but it might save a life. Just a thought.

[Mick D]

A "bolt-on" anti-rotational device would be a useful precaution.

Hi

In my opinion, the damage is caused by the bearing adjuster coming loose and causing the speedo gearbox to jam and then rotate.

Preventing the gearbox from rotating will cause the bearing adjuster to unscrew further and damage it's thread in the hub more extensively.

If I were to modify the system I'd be looking at positively locking the bearing adjuster - along the lines of milled slots in the adjuster thread to engage with a grub screw in the hub.

Regards Mick

[Dibnah]

I've not yet had the pleasure of dismantling an AMC rear wheel hub. Is the bearing adjuster part number 043355 ?



Edit: Probably varies from model to model

Earlier post on this thread by plugsnpoints http://www.jampot.com/article_read.asp?id=406 Matchless part numbers "> 021583 - Ring, adjusting, for rear hub and 021584 - Nut, lock, for rear hub bearing adjusting ring shown together <"

[ajscomboman]

I've not yet had the pleasure of dismantling an AMC rear wheel hub. Is the bearing adjuster part number 043355 ?



Edit: Probably varies from model to model

Earlier post on this thread by plugsnpoints http://www.jampot.com/article_read.asp?id=406 Matchless part numbers "> 021583 - Ring, adjusting, for rear hub and 021584 - Nut, lock, for rear hub bearing adjusting ring shown together <"

Nope that is a L/W drawing and doesn't have anything to do with this thread. It's the H/W's that suffer from the speedo locking up.

[Dibnah]

Thanks for the clarification.

From this article by Biscuit for the G9 & the G11 http://www.jampot.com/pic_display.asp?id=820

this image:



">
1. Circlip 010740. 2. Oil seal cup 018094 3. Oil seal 014387. 4. Ring, large 018095. 5. Collar 012436. 6. Spacer for oil seals. 7. Outer race. 8. Spacer 021586. 9. Ring, small 021585. 10. Adjusting ring 021583. 11. Spacer for speedo g/box 021594. 12. Nut, locking speedo G/box. 13. Locking ring 021279. 14. Spacer 021591. ? Not part of the assembly, just holds the sectioned bits together.
<"

Assuming that the H/W singles share these parts with the G9 and the G11 twins (?)

Edit: Biscuit's image disappeared! How did he create that image?

[Mick D]

Hi

The bearing adjuster is item 10.

The design of the assembly means that it is tending to unscrew under normal use and therefore if the lock ring, (13), loses torque for whatever reason the adjuster will tend to unscrew and jam the gearbox.

Regards Mick

[56G80S]

In my experience, Biscuit (Alan Jacobs) tip is the best guide. I've been very lucky with this over many. many tens of thousands of miles BUT dread when my luck runs out.

If someone, like Mick D, comes up with a preventative measure and clear instructions I would really welcome it and adopt it.

Johnny B