ND Speedo

bferris

bferris

Junior member
Location
Santa Cruz, California
Having just put a kit in my starter sprag clutch, the speedo on my '74 Laverda SF2 went out on the way back from a vintage meet. Cable doesn't seem to be broken but the ends look a little chewed up. If I disconnect the wheel drive and spin the cable with a drill, speedo seems ok.

I assume this is just ends of cable worn, but wondered how might check the bushing on the wheel drive. Haven't taken it off to take a look any advice on diagnosing/experience appreciated.

TIA
 
If the Speedo drive unit on the front wheel is similar to the triples, handle it with cotton gloves!
Don’t ask me how I know 🤔
it could be worn cable ends or it could be wear in the Speedo drive worm gear on the front wheel where the cable attaches to it which is what happened to mine.

Trying to remove the drive gear retaining housing resulted in a fractured casing!…..be warned 👍
 
The bushing is the item I was trying to remove, I certainly wasn’t being ham fisted and it took me by surprise 😳…..not a pretty sight.
Can you turn the cable with it just connected at the wheel?…with wheel stationary?
 

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Schurminater said:
The bushing is the item I was trying to remove, I certainly wasn’t being ham fisted and it took me by surprise 😳…..not a pretty sight.
Can you turn the cable with it just connected at the wheel?…with wheel stationary?
Click to expand...
Ohhh, ugly, ugly. I did put a wrench on the bushing to see if it would move, but didn't want to damage anything. Good instinct after looking at your pictures.

Good point, I'll try to spin the cable, if it does, I guess that indicates work cable (or bushing drive?)
thanks.
 
If that bushing doesn't budge with heat, etc, it is advisable to sacrifice it before trashing the housing. The bush is still readily available, the housing isn't/wasn't until recently.

The bush is brass and the flange can be quickly filed down, this will release the tension on the thread and the remainder screws out easily. Unless some moron has previously applied Locite to the thread...

I've reclaimed quite a few housings with laser welding, but Red now has billet housings on offer. Reckon these will be stronger than the originals.

The bush will wear on the thrust side if the hardened thrust washer has been omitted.

piet
 
If its indicating a speed with the drill on the bottom/wheel end of the cable, that points towards the gears being the problem.
I got a pair from Wolfgang. Might be worth checking him for stock.
 
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sfcpiet said:
If that bushing doesn't budge with heat, etc, it is advisable to sacrifice it before trashing the housing. The bush is still readily available, the housing isn't/wasn't until recently.

The bush is brass and the flange can be quickly filed down, this will release the tension on the thread and the remainder screws out easily. Unless some moron has previously applied Locite to the thread...

I've reclaimed quite a few housings with laser welding, but Red now has billet housings on offer. Reckon these will be stronger than the originals.

The bush will wear on the thrust side if the hardened thrust washer has been omitted.

piet
Click to expand...
Thanks for this. So, try with heat etc (or filing) to remove with it on the bike? Or remove from front wheel first?

I'll check for thrust washer...
 
I recently had a problem on my triple where the speedo would randomly start reading low on a ride. Turned out to be the internal square in the driven worm gear was slogged out. I couldn’t find a replacement - seemed only the drive gear was available - so had a cable made with a long solid square end crimped on. This currently works. I replaced the bush as it was also worn, and shimmed the clearance carefully for correct gear engagement.
 
Max said:
I recently had a problem on my triple where the speedo would randomly start reading low on a ride. Turned out to be the internal square in the driven worm gear was slogged out. I couldn’t find a replacement - seemed only the drive gear was available - so had a cable made with a long solid square end crimped on. This currently works. I replaced the bush as it was also worn, and shimmed the clearance carefully for correct gear engagement.
Click to expand...
Hmmm - thanks. I'll check that as well.
 
With the ends of the cable being chewed up, I suspect that's your problem. The cable inner should have clean square ends on it. It seems to me that the only way the ends could get chewed up is the cable not engaging properly. Maybe the inner was always a bit too short.

Do a simple diagnostic test before you pull the wheel apart. Put the bike on its centre stand and use a chock or jack under the engine to lift the front wheel off the ground. Spin the front wheel. If the little cable drive pinion rotates then your worm drive is most likely OK. Just to be sure it'll handle the friction load of the cable without jumping teeth, find something like a small screwdriver that'll engage in the square hole in the cable drive pinion and put a bit of resistance on the gears with your hand.

The speedo has already tested OK. If you confirm that the bottom end is OK, then it can only be the cable.
 
its the cable as Cam says,pattern cables very often do not engage far enough its that simple, I have had 3 from the same supplier (2 of them custom made with a speedo gearbox and clock cluster on their bench at £80+ and all of it money wasted) and none of them engaged, a NOS cable from an ex dealer who was aware if my problem solved this. Genuine NOS, the plating was fairly tarnished, like that bothers me! plus he gave it to me, a true gent, thank you Mr Bell.

What is not generally known is that the gearbox end of the cable is imperial, steming back from SF days when they used Smiths (ie imperial) clocks, the clock is metric, the crimped on squares are not the same, but pattern parts may well be, have you ever noticed that the gearbox end cable has a hexagon that fits a 16mm spanner quite well? (its not 16mm its an imperial size) and a flat has to be square with the disc to avoid contact, its imperial, a hex of 17mm would foul.
CLEM

I will wager that I will suffer by posting this.
 
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