Speedo/tacho drive..same part? - Lm

I’ve done about 100 miles on my newly rebuilt LM. After about 25 miles the optimistic speedometer stopped working. I thought it was going to be the cable broken or the speedo head which has sat redundant for a decade to be at fault, but on investigation some of the teeth have been “bitten off” on the speedometer drive gear. Also, despite being careful whilst removing the speedo drive, the hardened washer also seems to have been eaten by the gearboxOh bu**er it I am of course going to buy a new one, and Steine Dinse list a speedo drive that comes with the drive worm, but am I correct in thinking that the tacho drive is the same unit (but can be bought without the drive worm of course) as I can buy a tacho drive only without the worm and save some cash? I have a “reserve gearbox” built by Nigel of NBS which I will probably be fitting when I get the chance, and so assume that the drive worm will be in serviceable condition…hence not needing the drive worm. Apart from the disappointment of now being off the road as there is debris in the gearbox (and probably has been for the last 75 miles or so) has anybody had this happen to them and is there a usual cause for the teeth on the speedo drive being eaten?

ReggieV2013-04-30 22:11:03

The washer should not be able to move once the gear drive is in place, Are you sure it isn’t down the hole somewhere, they are very difficult to spot.As for the gears on the speedo drive having stripped, something must have stopped the cable from turning. Have you assembled the cable end and olive in the correct order? Is the inner too long for the outer and getting squashed when you tighten the ends up?Was this the original drive gear that you have put back in?

Inside the speedo drive in the gearbox end is a small ball bearing !!! if it is disloged ???

Well I have ordered the speedo drive set from S/D. Don-Spada wrote;something must have stopped the cable from turning.Yes, that’s what I’ve sumised on thinknig about it. But what? Don-Spada wrote;Have you assembled the cable end and olive in the correct order? Is the inner too long for the outer and getting squashed when you tighten the ends up?I think it went in in the correct order. If I recall, I put the drive into the drive let the outer sit on top and then nipped the olive up on the outer cable. Maybe next time I will not tighten the olive up too much. Is that the correct order? Don-Spada wrote;Was this the original drive gear that you have put back in?Possibly but not definately. guzzibear wrote;Inside the speedo drive in the gearbox end is a small ball bearing !!! if it is disloged ???Is this on the big twins? As I am lucky enough to have a spare g/box, I am, when time permits, going to “crab the frame” and swap it over with the possibly damaged box, which needs the end taking off. Maybe a job for Winter.I cannot find the washer down the hole, despite torch and magnets used, so cannot be sure if it disappeared before or after speedo drive removal.I have drained the oil in the damaged box, and there was a lot of grey matter in it, but it was working OK. Guzziology says that there are 2 hardened washers…one above and one below the drive spindle. I thought that there was only one below! I have put an order in for a new drive unit. I’m sure it’s the same as the tacho drive but have bought the drive that comes with the worm. I will compare the difference on delivery. Thanks for the replies.
ReggieV2013-05-04 20:19:53

Just curious, my 1965 stornello uses a very similar gear for the speedo drive of the front wheel, as do Lambretta scooters.The gear is made by Veglia. have they been using the same part since the 1960’s?Lambretta speedo drive

The body appears to be exactly the same, but the worm directional rotation and pitch is different.

To answer my own question asked originally, “is the tacho drive unit the same as the speedo drive unit” the answer is apparently no.

I asked Nigel of NBS, (who is checking out my originally fitted gearbox for damage)and he says that although they look the same, the pitch is slightly different.

As I have built my bike from an old dog, and a selection of bits appertaining to be nearly a complete bike, I think that I may have inadvertently fitted a tacho drive unit to the speedo drive. This would explain it eating the teeth in such a short time.

I just thought I’d post this in case it is of use to somebody else.

Interesting possibility! Did the replacement gearbox come with a speedo drive fitted?
Mike H2013-07-06 15:18:44

Mike H wrote “Did the replacement gearbox come with a speedo drive fitted?”

No, it came with the existing worm drive, so I bought a new speedo drive complete, and fitted the new scrolled drive into the existing (built by Nigel) worm drive.ReggieV2013-07-06 17:32:20

Sorry didn’t understand that. I meant the part you can just put the cable into. Just that if already present then should be the correct one, all I meant.

Mike, I have had to fit the speedo drive and 2 hardened washers myself.

So room for error/disaster again…but I don’t think so.ReggieV2013-07-07 11:58:51

OK then! Ta