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.â€
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 gearboxâ€. (
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 driveâ€. (
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 arrowâ€. (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