I had another look at my misbehaving odometer, see image below. A couple of questions if I may. Is the eleven tooth cog original, or would it have been white plastic? It seems pretty fixed to the spindle, so I'm not sure it is slipping under pressure? The teeth on the right of the white screw (is that the right name?) they do look a bit worn. Do they drive a separate mechanism that turns the trip counter? Or is that being driven by the main cable? The orange residue on those teeth doesn't look encouraging.
I believe the gear to the right is an output of a reduction gearbox off the input shaft that also spins the magnets that drag the aluminium cup to move the speedo needle. That then drives the worm gear that drives the cog which I think drives the whole stack of counting wheels, both the main odometer and the trip wheel so that they both count miles or Km in step based on the number of teeth on the cog driven by the worm gear. [The orange residue will be an original oxidised grease of a type that doesnt knacker nylon. Water, most mineral greases, mineral oil and WD-40 soak into nylon, make it swell up and crack.] Same for the grease in a windscreen wiper gearbox. If its slipping elsewhere then its time for either a skilled strip down and clean up and reapply silicone grease, or muchos pesos over a swapmeet table.. I didnt ask the price as my bus is RHD, but there was an LHD cluster with trip meter and a clock at Volksworld in the swapmeet...
It could be that the cog is fitted the the collar facing out then it does not line up with the corkscrew correct could potentially cause slippage, try and remove and turn round.
Good point. You can't really see from the angle of the photo, but the teeth of the cog are offset slightly from the top of the screw, so may not fully engage, which is why I originally thought it might be 'jumping' rather than slipping on the spindle. There was no movement on the spindle when I checked for slippage, so it might be difficult to shift, but worth a go. Thanks.
The proper cogs have a slight angle to the teeth, so they dont bind with the worm gear drive. The brass gear has teeth in line with the shaft so you cannot push it fully into proper mesh with the worm gear, or it will bind. Properly cast gears will be better, or if you file the teeth of the brass gear so each tooth is more a diamond shape seen from the side, with the contact angle matching the angle of the worm gear. Or 3D printed with the correct spiral on the cog.
I to have a odometer that's got a trip counter in MPH the original cog was made out of plastic, I bought the plastic cog from here http://m.odometergears.com/mobile/products/Volkswagen/Mechanical Speedometer/19 a few years ago, last year I had a fault with the speedo part where the needle part would be at 15 mph when stationary & then be around 15-20 mph out all the time, I then sent the unit here http://www.jdo1.com/index.html to be repaired. I got it back in a week all sorted.
Well there's a thing! Having fixed my odometer I now find the speedo reads low (approx 10kph) - When I dismantled it I moved the needle past the rest stop to get the correct pretension, and did the same on reassembly - i/e. the resting position was, say, 7 o'clock - then moved it over the stop so it had (I assumed) the same preload on it.... wonder what's gone wrong?
I don't think we'll be setting up a speedo repair business anytime soon! Fix one thing, another problem crops up...
I think you’ll find there’s a dot or line (can’t remember but will dig mine out) on the lower part of the speedo face. If you gently lift the speedo needle anti clockwise over the pin, this is where it will point to at rest. When you turn the needle clockwise, its rests against the pin with the lightest of preload on the spring. This calibration method has worked for me when I replaced a broken speedo needle. This is not VW fact from factory or anything. Just what I have discovered. Stirlingmoz
There are two dimensions that might make a difference - the zero setting and potentially the spacing between the magnets and the aluminium cup that drives the needle, working against the spring. The zero of the spring causes a constant offset in the reading. The magnet spacing would alter the amount the needle moves for a given increase in speed. So a reading that is 10mph low across the range but the reading changes by 30mph between eg. 50mph and 20mph road speeds is a spring zero point issue. That would indicate 10mph and 40mph on the dial. But if it changes by e.g. indicated 20mph between 20mph and 50mph road speeds that will be the magnets and the cup. That would indicate e.g. 20mph and 40mph...(assuming the zero is set correctly.. )
