Page 1 of 1

Speedo trouble shooting and drive repair...

Posted: Thu Dec 27, 2018 11:59 am
by Prof
Speedo on Paul's recently purchased Honda Steed was not working. Is the problem in the speedo, cable or drive? Let's find out.

Step one... Separate speedo and cable, jack up wheel and spin it. If cable is turning it will be a problem with the speedo. As a double check, while spinning the front wheel, grip the inner drive at the top of the cable as it spins to make sure it will work with some pressure on it. Cable is not turning, so is it a broken cable or speedo drive?...

Step two... Disconnect bottom end of cable from speedo drive. Some cables screw in (HD's through to 90's). Others have a threaded collar the same as the speedo end. Others (eg 70's CB's) have a phillips retaining screw which often needs an impact driver to remove. This one has a phillips screw. Spin wheel and the drive spins. However in the case the driving blade that inserts in the cable has snapped off.

Now, why would the silly thing do this? A big mistake riders make is to restrain cables with cable ties. Hey man, that's not freedom! The less restraint you put on cables (clutch, throttle and speedo [especially speedo]) the less likely they are to break and in the case of throttle and clutch the easier pull you will have. Cables like the wind in their face as much as you do, so unless you have to keep a cable from touching an exhaust or in the case of a speedo cable, the front wheel, do not restrain them. If a throttle cable swings out in the wind, again, minimum restraint.

So back to our speedo drive...

I could go buy a new drive ($$$$$), find a second hand one or try repairing this one.

We'll try the latter. So to dismantle the drive, remove it from the axle. Drives consist of...
1. an aluminium body,

2. a drive ring (red arrow) that has lugs or depressions (blue arrow) that locate in the wheel hub. This worm drive retainer (bottom) is a press fit,

3. A worm drive with a male flattened, or squared end pin that locates in the cable. Or the cable may have the male connection. You can see the broken off male piece of drive blade to the right.

The worm drive has a bearing surface each end that usually runs in small brass bushes. Older ones are retained by a screw, pin or circlip at the cable end. Later ones use the cheaper course of just being pressed in...

This drive has the latter, so i grind off the bottom end so the worm drive can be driven out with a drift punch. After reassembly we will reseal it with a dob of silicone or you could use epoxy metal...

With worm drive removed, I build the end up with MIG weld...

Carefully grind,file or linish it to match the shaft.

1mm angle grinder disc then used to cut two flats. Make sure the flats are parallel and centred...

Check for fit...

Reassemble... Grease well. When reassembling worm drive you need to be careful of tolerances. The worm drive needs to be free to rotate, but not slide forwards or backwards. If the retaining collar is not pressed in enough, the drive will engage and turn one way, but jam the other. So it might work fine when your chopper moves forwards, but jam when you are wheeling it out of the shed... one broken worm drive of stripped drive ring (which are usually plastic)...

Once reassembled (grease axle and all threads and run some oil into the top of the cable) spin wheel and do your cable test again...

When rerouting the cable, keep it straight as possible with no tight bends (green arrow). Clutch cable on this bike (blue arrow) followed a very convoluted route and had about 6 cable ties. You can see the tight bends still showing. Clutch had a very heavy pull. Once rerouted and only one cable tie to keep it away from the exhaust and clutch is much much lighter... and will now last a heck of a lot longer...

All reassembled. Spin wheel and make sure drive was the only problem. You can usually get it up to 10kph which will show on the speedo.

Took the Steed out for a couple of hours including some pretty rough roads, and speedo still working fine. Hopefully it will now be fine for a lot of miles. If you are unsure of your repair, this approach at least gives you a chance to find another reasonably priced drive.

If the cable was broken, they are not too expensive to replace. I have cut speedo outer cables in half and bronze welded the broken inner cable and rejoined the outer with some pressed sheet metal... lasted for years.

Speedo repair is another matter altogether, but if you can't get the correct speedo, you will find that the speedo ends on Japanese cables usually only have a couple of variations, so it is not hard to find a speedo that will fit. Calibration is usually done according to wheel diameter, so pick a speedo of a bike with the same size wheel as yours. If you end up with a speedo that doesn't calibrate right, some white painted dots or lines can be painted on the glass to show the main speeds you need to know; 25k, 50k, 80k, 100k.

Not a complete treatise, but still hope this has been helpful. Ride safe. Lots of blind and inattentive drivers out there!