Speedo Question

I know that this has been brought up numerous times and the ultimate solution is probably forget about it and just watch the tach, but I've had speedo problems for the past 3 years and am now on my 3rd speedo drive. Bike is 74 Mk II and the latest installment of the drive issues was replacement a week ago. Seemed to work but erratic at low speed and than would steady out at high speed, i.e. 50-80 mph. Figured I could live with erratic at 20-30 mph since I don't ride there that often. But predictably it failed the next day.
I pulled the cable to check lube (lubed in one of the earlier installments, and it didn't look that good. Had a small knob at the end (?) which seemed to be loose. So I bought a new venhill teflon cable. Cable works fine and clock turns when used with a drill (anti-clockwise).
Anybody have any idea why the early mortality for the drive? The original lasted for about 16K, the replacements fail quickly. At $135 a piece its a bit much. However, I do like knowing the total mileage.
This can't be that big a mystery and I'm sure its the mechanics fault (me), just would like to stop breaking them.

My understanding is that if the cable is not right and protrudes into the speedo or tach, it does bad things to the unit. What I have heard is the end of the cable going into the clocks, the inner part should not protrude any farther than the end of the nut when it is pulled tight to the end of it's sleeve. It could be too there is no stop on the cable and during operation the inner cable is wandering around inside the sleeve and pushing up into the clock? Just a thought.

Dave
69S

Don't want to offend anyone, but in my opinion they dont last because they are complete junk! I have had ones which don't fit, ones with malformed threads and all of them fall apart, often within a few weeks. I have left the Green Spot on for the looks and depend on a £10 cycle speedometer that so far has outlasted about 5 drives. I refuse to waste any more money or time on substandard kit. I have been in touch recently with SRM who hope to have electronic green spots available later in the year. For the money I have thrown away on POS speedo drives I could have bought one already!

David

Plenty of good info on speedos and how to keep them going. Did you try the search?

Have a look at Stuart SS Thread on his trident, he fitted a nice gps unit gets rid of all of the rubbish

Some consider the Commando speedo drive and cable to be an actual safety hazard, I removed mine 20 years ago.

seen too many cables grabbed, twisted, and torn from both ends, even saw one wrapped up in the spokes.

I am going to own my bike until I die and could care less knowing how many miles it goes or how fast it goes.

I keep the tach in good shape and have the speedo on the fork tops for symmetry next to the tach.

Clock end don't bother the drive unit, just the read out and clock damage. Drives can fail in a few ways. Most common is the rivets wallow out so ring gear mis aligns til chewed up. Top hat spacer missing or smashed down too much squeezes the drive to death faster. The worm gear end caps get loose so worm gear mis-aligns and screws itself to death and shifting back forth on speed changes. I try to keep two on hand expecting about 5000 miles before intermittent needle action starts, again but surprised Trixie's gone another ~8000 miles starting with 6000 on oddometer before I got her, so extra surprised. But last 1000 the clock end of cable is apparently moving for intermitent needle activation, so I suspect the drive worm-caps are in wiggling wear phase now. Once over 75-80, indicated, steadys right down with one to one response to speed changes. On THE Gravel will activate needle on washborads bumps at 30-ish, then drop on another set.
Grease it enough to matter long and excess shows up on hub till seeks its innate amount.

What lube is prefered?I cant find any info on that,Some say only oil.Going through the same thing myself,but I want
it to work.
YING

I'm still on my original clocks, and cables.

Dave
69S

I still have my orginal drive and cable (36 years now) with over 120,000 and have never had any problems with them, the orginal clock has been rebuilt ( was in a major fire 30 years ago) and was save (rebuilt 18 months ago) but have had the needle fall off twice now first time a week after the rebuild and again 2,000 miles on it, has been put back on by the rebuilded at no charge and have put it away and put the Smiths speedo from a Triumph that has been on the bike for 30 years without problems.

Ashley

Ying, regular grease in a gun to the nipple works fine. I have had one sieze-up on the road though ripping the cable out and slurping into the rear wheel spokes. Worked out the cable and flung it into the ditch and continued on my way. I believe this event was caused by lack of regular small amounts of grease.It was a busy summer.

Before I realized the speedo drive was supposed to have top hat spacer, had one grab hug and jerk cable out of clock to wrap up but was going slow on pasture so just slid to stop about side ways. Had one drive the cable pulled out the worm gear cap and get snagged under tire, but felt and tied up before tripped down on THE Gravel. Commandos are special, stuff that wouldn't bother other bikes can be dangerous to ignore. Get married a few times &/or own a Commando or two to get proper perspective of level of man hood to endure the curve balls.

I hated to even ask this question since I think I know what the ultimate answer is. But just a little frustrated. Cable is a new Venhill teflon and I was able to spin the clock. After putting it back on the drive unit it worked perfectly. Least bounce I'd ever seen (so I figured mechanic error which considering I'm the mechanic it isn't surprising). Next day doesn't work. Since the drive unit is new and really has very few miles on it I think I'll reinstall it and make sure that it is aligned well on the wheel and try again. The only thing about knowing the mileage is its good to have an idea when you need gas. Since this can be done by looking in the tank its not a necessity. Also I do tend to lose track of time between oil changes and like to change it every 1000 to 1500 miles.

Sorry about mentioning oil. Bad topic to even hint at.

Unscrew the cable from the instrument ,go around the block observing the raw exposed end to see if the cable is turning. Elimination. Mind the neighbour's cat or goat that jumps out in front of you whilst your eyes are on it. The cable end can be reinserted for another test. The end of the cable must be square to do it's thing. I once ordered a new cable to find so much solder it was rounded. A file worked.

Are we talking about repros or the real thing? Heck my speedo drive is original with 37000 miles on it.