The Dreaded Speedo Gearbox

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Mick D
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Re: The Dreaded Speedo Gearbox

Post by Mick D »

Hi

Whilst the AMC design wouldn't pass current scrutiny it's by no means unworkable.

How many of these issues have occurred using original components? If the speedo gearbox is not secured by the lock nut it will tend to rotate but the cable will restrain it, over time and repeated use this may allow the retaining nut to back off sufficiently to allow the gearbox to tilt to a point where the gearing jams and causes a destructive incident - but I like to think this is uncommon.

If a new gearbox or bearing adjuster is installed where the manufacturing 'tolerances' mean that they are in conflict then additional shimming will be required to avoid this type of failure.

I tend to believe these issues are down to the quality of replacement parts, which, whilst useable, are not direct replacements.

Regards Mick
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Dibnah
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Re: The Dreaded Speedo Gearbox

Post by Dibnah »

Mick D wrote: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
Ta, does "10" rotate in normal operation?
Mick D
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Re: The Dreaded Speedo Gearbox

Post by Mick D »

Dibnah wrote:Ta, does "10" rotate in normal operation?
Hi

Yes - It rotates with and is locked to the wheel hub.

Regards Mick
56G80S
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Re: The Dreaded Speedo Gearbox

Post by 56G80S »

Mick D,

That's a sound point. I am still using the original parts that came to me with the Matchless in the mid 1970's and, for once, I have ket the gearbox appropriately greased.

There's a good case for measuring and carefully re-assessing the new parts prior to fitting. I have tended to use the Club, AMC Classics and Russell's (and back in the day Joe Francis) for parts and have thought that their supplies were good to fit straight in.

From what I'm reading, much more care, maybe caution, is needed.

This hasn't helped Dibnah, but certainly has helped me.

Johnny B
bob121
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Re: The Dreaded Speedo Gearbox

Post by bob121 »

Just for clarification. My incident on the m1, I believe was caused by the adjusting ring working its way loose. When I was reassembling the rear hub assembly, for whatever reason I had to undo the locking ring and the adjusting ring turned with it at least a full three turns before the lock ring let go of the adjuster. Originally it was the speedo drive failed. But this time I believe it was the adjuster that failed. Hopefully drilling the hub and fitting a locking screw into the groove in the adjusting ring will work.
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Duncan
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Re: The Dreaded Speedo Gearbox

Post by Duncan »

Just a couple of pondering thoughts, no answers:

Of the wheels that have locked up did they have the washer under the speedo locking nut or not?

I have known the spindle to be difficult to remove as it have "welded" its self to another part indicating heat from turning, if the problem was the adjusting ring 021583 unscrewing and wrecking the speedo gearbox nothing should be turning against the spindle? Could a loose spindle be a culprit allowing movement between the spindle and say the oil seal spacer?
McMaz
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Re: The Dreaded Speedo Gearbox

Post by McMaz »

I agree with Mick D's and Johnny B's comments about being cautious when replacing parts. I have been doing a bit of trawling about this forum and the web to try and get some more information on the potential problems around the rear hub/speedo drive. I stand to be corrected, but I think problems may possibly arise in the following areas, either on their own or in combination.

Assembly of the rear hub:
In particularly the correct sequence and orientation of the oil seal and metal cup – (see http://archives.jampot.dk/technical/Whe ... odruff.pdf). I know that from when I came to assemble my hub, when you've got the parts in front of you it seems counter intuitive that the oil seal is not be located in the metal cup but, as Wayne makes clear in his instructions, the wide side of the metal cup faces AWAY from the oil seal. Also, it is crucial that the speedo gearbox lock nut must not under any circumstances be tightened with the wheel out and not before the wheel spindle nut has been fully tightened

Speedo drive gearbox:
Obviously, lack of lubrication could cause problems – (see clive's post at the bottom of http://www.jampot.com/forum/viewtopic.php?f=18&t=15671).
Looking at the information on replacement drives at Gaggs, (http://www.gaggs.co.uk/html/drives.html) it appears that replacement Smith's speedo drives are thicker than the originals and “when replacing the earlier type with the latest type the correct thickness spaces must be used so as not to exert too much pressure on the gearbox casing causing damage to the drive gears.”
Several members on the forum have said that they found it necessary to make up and add a spacer so as not to crush the replacement drive against the lock ring. I think Dave Walker came up with a good suggestion, he says “I used a spare 021604 dummy spindle washer which I placed between the outer flange of the speedo gearbox spacer (021594) and the inside of the speedo gearbox”. (http://www.jampot.com/forum/viewtopic.php?f=19&t=2228)

Rear bearing adjusting ring:
My suspicion is that this may be the culprit in a lot of cases and especially where repeated lockups have been experienced.
On the forum there is this from ‘bob' – “Several years ago I replaced the Speedo Drive gearbox with a new club one , but not the drive ring. First run out and the back wheel locked up, fortunately only doing about 30 mph and on a quiet country lane, but it was still a serious Brown trouser moment. Contacted spares and was told I should have been advised to replace both together. As new gearbox is not compatible with the original ring.” (http://www.jampot.com/forum/viewtopic.p ... b.#p159704)
And there is this from ‘TRFell' – “I had this happen, but the bearing adjusting ring that locates in the dogs of the speedo came undone , unscrewed seizing the back wheel, there is modification if you have access to a lathe. A modified adjusting ring 021583 is recommended if the ring is not truly concentric with the speedo drive”. (http://www.jampot.com/forum/viewtopic.p ... 3&p=218789)
The only technical reference I can find for the replacement or modification of the adjusting ring can be found on page 68 of the Matchless ‘Workshop Instruction Manual All Models, 1957-1964' (http://archives.jampot.dk/book/Workshop ... CHABLE.pdf).
It states “SPEEDOMETER DRIVE (Heavyweight Models) Should the bearing lock ring (29) come loose and unscrew the bearings, this could be associated with the speedo gear box. If the adjusting ring (30) is not truly concentric with the speedo drive, the tightness of the lock ring can be affected. A modified adjusting ring 021583 is recommended, or if machining facilities are available, existing part is altered to the dimensions shown in Fig. 85. The old part number is still used for the modified type. The new dimensions are ringed, also indicated by arrow”. (I suspect the accompanying technical drawing, Fig. 85, on page 69 may have somehow been inadvertently slightly cropped on the right-hand side).
Club spares stock the modified adjusting ring (021583) but there is no information about why or when it should be used.

Sean
56G80S
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Re: The Dreaded Speedo Gearbox

Post by 56G80S »

Sean

What a useful post, thanks.

On another forum I use, there are "stickies" where particularly useful threads, usually where safety related technical matters are solved, are held once complete as reference points and no longer susceptible to replies unless authorised by an administrator. Just a thought.

Bookmarked this for myself.

Johnny B
bitza
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Re: The Dreaded Speedo Gearbox

Post by bitza »

If you check out GAGGS of Nottingham web site they have some useful info regards speedo and Taco drives, also drive cables, and they do repairs and restorations of same.
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Dibnah
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Re: The Dreaded Speedo Gearbox

Post by Dibnah »

A mine of useful info on this thread, as with many others on the forum. Bringing together some info, perhaps mainly for my own benefit:

Reducing risk of failure:
mikeydpippin wrote: I've marked the Speedo gearbox and the locking ring with a small red mark and will be keeping an eye on the marks also periodically checking the gearbox to check If it's getting hot 🤞🤞and of course watching the cable for any movement at the gearbox end...
and
Mick D wrote:Hi Mike

I'd add routinely checking the rear wheel bearing play to your confidence checks.

Mick
Rear wheel bearing play can be measured by rocking the wheel, this thread suggests 1/64 inches at the rim, which I calculate as 15 thou, which is not very much:

http://test.ajs-matchless.com/forum/vie ... 17&t=17815

My Matchless 500 has about 60 thou total float at the rim (extreme to extreme) but also has some loose spokes.

I've had the rear wheel apart (QD), this thread was useful re: undoing "12. Nut, locking speedo G/box" before dismantling.

http://www.jampot.com/forum/viewtopic.php?f=19&t=4791

On the speedo gearbox side, this "top hat" spacer/bush is aligned with the larger diameter inwards, is that correct? It's probably "6. Spacer for oil seals."

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