Speedometer fix (replace magnet) and headlamp wiring

My speedo looked OK but didn't deflect when riding. Further when  I connected the new cable it just rotated with a knocking sound. I therefore removed it. I found that if I pushed just the inner cable in really home then I could get a deflection when that was rotated by hand. However it was inefficient (slipping cable?) and didn't return to zero unless shaken or tapped... it seemed to stick at around the 5mph mark.

The speedo is not made to come apart... its held by a metal cover plate on the rear which is clipped under the plastic rim on all 4 sides. It might "unpop" but that seemed very likely to break the plastic lugs on the case.  Opted to make a controlled cut. There are 2 slot  recesses (one each side) towards the flat edge of the speedo. These are use by the wire clip that holds the speedo in place.

I opted to use a hacksaw to cut across the flat edge lose to the bottom but within the depth of these slots to detach a strip of plastic from the lowest side of the speedo in the hope that the plate could then slide out.

Strip detached. The metal plate did indeed then move and a combination of levering and sliding allowed it to come out.

The cable entry hole appears rounded... it should have a square shape to grip the cable and I suspect this explains the knocking noise and failure of the cable to register unless firmly jammed in.

The innards coukd be finagled out

And the indicator needle just pulls off

The indicator card face is held on by 2 bent tabs and easily  removed by straightening them.

The indicator face comes off but thats about as far as I could dismantle it. The brass cog and worm screw gear drive the odometer via an internal nylon shaft. There is a large rotating mass (damper/fywheel) shown here just below my thumbnail. This turns when the cable is rotated.

Removing the face reveals a coilspring located above the odometer. This is responsible for returning the needle to zero. I'm guessing it's either become too weak or the indicator has slipped on its drive pin. In any event the answer seemed to be to apply some preload to this spring.

I reattached the face and then, holding the unit in one hand I could use my fingers to rotate the flywheel damper against the spring before refitting the indicator.

Releasing the flywheel allowed the indicator to spring back to zero. I sprayed the working parts with light oil to flush out any muck, cleaned off the excess and cleaned the indication plate and inside the case. The mounting clip as seen below, slips through the slotted recesses in the case to enter these locations on the backplate. When the clip is activated it applies pressure onto this base plate, bracing it against the inside of the nacelle and so pulling the speedo down into the nacelle. This is why it was important not to cut below the slot recesses in the case. It should also mean that my cut has not affected the mounting mechanism (nb reader... I may have been wrong about that).

I reattached the strip of plastic I'd sawn off. I think the best way to do this for a permanent repair is probably with a hot glue gun. Obviously there is a "saw blades width" of plastic missing where the cut was made, and the hot glue would be able to fill that. I wasn't sure whether I'd be revisiting the contents so opted for evostick at each side and reinforcing tape.

The mounting mechanism still worked and I could refit the speedo. However the cable still misses inside the drive socket so I don't think this has solved the problem. My initial thought was that  the speedo drive socket is simply too worn, it's rounded over much of its depth and the cable inner isn't long enough to push in deeply enough to engage with the undamaged section. I've ordered a new cable in case mine is the wrong version and too short, but if this doesn't work I'll have to investigate shortening the outer cable by a few mm so that it can push the driving cable more deeply into the drive recess. This will be difficult since the terminal is crimped.

OK... well I tried that but it made no difference. There is clearly something wrong internally. I have in fact, ordered a new speedo so I figured there was nothing to lose by investigating further... this may not have been strictly true as parts are not available.

I removed the mechanism once again. This is in 2 sections held together by 2 bent metal tabs. A further 2 anchor the speedo drive shaft locating plate.

You can see one of the 2 section joining tabs here.

The speedo consists of 2 or 3 sections held together by 4 bent metal tabs... thers one at 12 o'clock in the picture and one holding the lower section further down. In addition there are worm drive shafts that are held in place only when the parts are joined like this and will fall out as you disassemble it. Straighten the tabs and start to ease the 2 sections apart

Separating the sections

The speedo drive section comes away from the upper (indicator) section, the brass worm screw driving the trip meter comes out as you separate the sections.

Here I had a surprise as there is no shaft connecting drive from the drive section to the indicator section. Looking inside the driven section provided the answer as rotation in this section terminates in a flat ring magnet

This engages magnetically with cup on the needle drive in the indicator section.

Indicator section odometer shaft position. Cup to engage with disc/ring magnet shown below

This is the explanation of my problem. The disc magnet had simply lost magnetism and was no longer firmly paired with the indicator drive segment. The magnet is mounted on a shaft that connects ultimately to the drive cable. There is a large circlip on this assembly just below the magnet. I removed it because I'd assumed it was necessary to review the shaft... in fact its not and I dont think this is necessary. It doesnt seem to hold the shaft in place... i think its more to do with the magnet although removing it didnt help with magnet removal either. On the whole if youre doing this, Id say ignore it as it gets bent by removal and may not go back correctly either.

Disassembled speedo... note the clip I removed probably unnecessarily.

The nylon odometer link shaft then falls out, and the magnet drive shaft can be removed.

The underside of the magnet shaft has this sliding lugged plate... this slips over the shaft and then slips to one side to fix the shaft height. The plate has 2 of the fold-over clips that hold it in the case. Overall this arrangement seems to hold the magnet at the correct distance from the needle drive cup and this provides an excellent reason not to remove the shaft from the magnet head as this system sets the distance from the rotating magnet to be rotating cup... presumably at the optimal for obstruction free rotation and magnetic coupling.

I do not believe it is possible to re-magnetize this ring magnet. I tried, but everything I did simply removed any residual magnetism. I suspect this was a complex industrial process resulting in a round bar magnet that's been sectioned to give the ring above. It's not a simple N & S pole.

The ring magnet is 24x14x3mm in size and presumably could be replaced. If not by a solid ring, then a series of individual disc magnets should work as long as they don't exceed 3mm thickness. There are several candidates on eBay. I was going to pursue this when I made a serious mistake. Whilst trying to see how the speedo indicator section worked I accidentally rotated it backwards. This was disastrous in that it completely destroyed the spiral needle return spring which unwound and twisted. Do not rotate the speedo backwards when it's disassembled... ever! Initially I had thought I could simply replace the spring but this appears to be a difficult and delicate process since the new spring needs to be attached via a collet to the needle driving shaft and retained by a wedge to the speedo frame. Obviously there is no VDO speedo spares shop so I sought replacement springs via watchmakers etc. I'd expected them to cost just a few pence... but surprisingly no! They are very expensive either to buy or in postage from the EU. I don't think the speedo spring is particularly critical... it simply returns the needle to zero and shouldn't affect the indication ... unless maybe its very, very powerful (!). Anyway it's only a moped that can't exceed 30mph so accuracy isn't going to be that critical. Watch springs on the other hand are precision items with defined torque and wire sizes and I suppose this explains their price. I dont have those details for the spring I need and so I think any cheap replacement that fits would do. I may continue this repair at a later date, but for now I'm going to pause it. A new speedo is £72 and it seems magnets could easily run to £20 plus... with of course no guarantee of success. Currently that seems like a bad investment so however much I would like to try, I'm putting it on hold unless/until suitable parts become available at a reasonable price.

PART 2

I found a box of cheap spiral springs of various sizes on ebay, so decided to attempt repair the speedo. Surprisingly new springs come with collets already attached which really simplifies things.

The remnants of the old spring are held onto the indicator neefle driving shaft via the collet. To remove this,  force a knife or scalpel blade into the collet's split line. This opens it up and the collet will then simply slide off attached to the knife... as below with the remnants of my destroyed spring still attached.

I chose a new spring.... prob too small, but using the knife again in the collet slot I was able to pick this up and position it onto the spindle. 

New spring below.

The collet tightens as you push it down onto the indicator needle shaft. I'd found the previous collet had been fitted with about 1mm vertical free play, so I pushed this one down to almost the same level. Note that you have to fit the spring the correct way around!

The free end of the spring pops through a hole in the frame and is retained by a push pin. The pic below shows how this works....

 Obviously key to this fastening is the push pin... I knew exactly where I had stored this... right up to the point where it wasn't there and thus refitting the spring was greatly complicated.

I needed to make a new pin but I didn't have anything the right size. But I did have a set of dental drills and so enlarged the retention hole using various fine drill sizes. I could then cut a section off the drill bit I'd used, and file this to a point. I could then use the drill fragment to replace the push pin. Result below... the spring is a little weak but it does return the spindle to the rest position. I do have a bigger spring but I'm going to test whether this one works first.

Drill fragment as retaining pin.

Replacing the magnet

I didnt know how to go about doing this. It seemed to.me that the shaft might need to be removed in order to remove the magnet so I tapped it out. Turns out this doesnt help with magnet removal and you dont need to do  this; it just made more problems in reassembly as it destroyed the distance swtting between rotating magnet and the cup it drives. If youre doing this job, dont tap the shaft out.

 

Tapping the shaft (unnecessarily) using a drift and socket.

The shaft came out relatively easily.

But sadly this didn't release the magnet and it didn't lever off readily either. I used a dremmel to make slots in the magnet... taking care not to cut into the supporting disc.

I made several cuts and levered the segments out

These came of easily but the plate was a little damaged and it will not be easy to load new magnets onto it. In fact the position was even worse since these ring magnets are not available. They are still being made (presumably) since new speedometers are available, however they aren't retailed and VDO wouldn't sell me any. As I couldn't find ring magnets that would fit here I opted to buy smaller magnets to place in a ring round the cable driven disc. The original magnets are ferrite but modern  neodymium magnets are much stronger so I ordered some 2mm x 3mm cylinder magnets. The plate they need to fit onto is aluminimum so they won't attach by magnetism alone so I used araldite. I only fitted 2 magnets to start with.

Magnets glued 180 deg apart on speedo drive disc. I don't think the circlip I had removed serves any purpose but in case it acts as a mass for momentum I did refit it.

Obviously I had tapped the shaft out and lost the distance setting. However, as Id now changed the magnets both in size and type Im assuming some adjustment would have been necessary anyway. I pressed the shaft back in using a vice. The depth of push is critical since the shaft is held by the cutout plate and if the magnet bearing disc is pressed in to little then the magnets will foul the dive cut and the two sections of the speedo won't fit back together. 

Above you can see the magnet plate isn't pressed on enough and so it's sitting too high. I had to press it in a little more in several little stages until the speedo would close closely and the cup would rotate when the shaft was turned. Finally hold the cup and turn the shaft to check it could move without scraping on the magnets. I could then reassemble the speedo halves.

 

You have to insert the drive shafts for the odometer as you put it back together and check that their mounting holes are lined up. I inserted the nylon shaft, then the magnet drive shaft and finally the odometer top together with the brass drive shaft. 

 I had accidentally bent the spindle mounting plate out of shape so had to take care that the shafts fitted into their location holes as well as the fixing tabs into their slots. There are 2 locating pins next to the tabs for the 2 halves so make sure everything is fitting together properly before securing by bending the tabs.

I could then replace the speedo plate

And secure it with the tabs behind

Add the indicator needle

 I fitted a speedo cable temporarily to the assembly to check that the needle deflected when the cable turned. I could then refit the mechanism in to the case, clipping the metal back plate into position.

Finally, I refitted the strip of plastic I'd removed to open the case, holding it temporarily in place with tape.

whilst I repaired it with the hot glue gun.

Obviously I have no idea of the durability of this repair but I hope it will last. It should also be said that I don't know whether the speedo is at all accurate, but its back together and works when you're moving.

Headlight wiring

I hadn't tested the headlight whilst the bike was running (forgot) but didn't expect any problems. However the rim was badly oxidised and pitted and this had to come off for replacement. That meant detaching all the wires. This isn't so much of a "how to" section, more simply a record of what's connected where with a few notes.

Connections; single blue, single green, red and yellow, red and grey (thinner). Note stump of unconnected red below the red plus yellow connection. I think this is superfluous but I need to check.

Brown wire earths bulb holder to headlamp rim plate. Strangely there was no earth to the terminal, instead a brown earth wire ran from the horn mount to the headlight adjusting screw, presumably providing a roundabout path for the return current. I'll take this wire directly to the earthing terminal when I rebuild.

Brown earth wire goes from headlight adjuster screw (seems a daft place... is it original?) 

Brown earths the  headlamp rim to horn mounting bolt behind the horn (horn detached in pic).

Wiring to lighting switch inside nacelle.

Thin grey wire is I think power feed to the horn. The horn itself has 2 grey  wires... both are thin and I think have been replaced. One is power in (from the lighting switch?) and the other must connect to the push button but I might have these the wrong way round.

Unscrewing the adjuster to release the headlamp rim... note this also detaches the brown earth.

Adjuster screw with its square nut... also the poor brown earthing contact wire.

Rim then detaches with glass

And can be separated from the glass.

Note foam edging to backplate

The mysterious stump of red wire...?

I tested the bulb which still works, cleaned all the contacts and the glass. I replaced the headlamp rim with a "good used" one from stock and put the original into citric acid to try and remove the green oxidation and pitting... which was very effective.

I reassembled the light trying to reconnect it as it was. However grey and blue wires were a little faded so colour I'd was sometimes tricky. I won't know if I've got it right until I can power it up.