Aprilia S1 speedometer

[brian]

I am new (relatively) to Aprilias and have an odd problem. The speedometer was working normally and really very accurately before the SPR when it stopped working suddenly. On the whole of the rally we did 3.2mls!
After the rally, I took it back to Speedograph Richfield who said a return spring on the tripmeter was the only problem. I drove the car without the instrument and the cable was rotating nicely at various speeds and with some force when I held it. I put the repaired instrument back on and it still does not work. Or rather it sort of does; in 12 miles it showed no speed but did rotate 0.3mls.
I took the cable and the instrument back to S-R and they tested them together and there is no problem.
They say the issue is in the drive from the gearbox probably not giving enough torque.
This sounds a bit fanciful to me but before I try to take off the mount at the side of the gearbox I thought a plea for advice would be sensible.

[ColinMarr]

I once had a similar sounding problem with my Fulvia. I think this was to do with wear on the end of the square-section taper at the end of the cable as it is supposed to engage with the drive from the gearbox. Richard Fridd guided me to shrink-warp tubing to fit over the taper to take up the wear. It worked for me and maybe will for you.

Colin

[BlueSky]

Brian your problem could be a number of things. Assuming the speedo is ok it might be the cable, could have a kink or getting frayed, never assume the repairer says it's fine. Is the small screw used to hold the cable on the output of the speedo fitted correctly? If it is an issue in the right angle drive off the gearbox it's very easy to remove to check, a quick inspection should reveal if the gears are worn or the cable not inserted correctly, it's held in place with a small bolt. Or it could be the speedo gear on the output of the gearbox main shaft has come loose.
I've attached the diagram from the 1st series parts manual if you don't have a copy.
Have look though the experiences I had with mine a few years back, might be helpful or not!
http://narrywoolan.com.au/lancia-aprilia-1070/metron-speedometer.html

Noel

[davidwheeler]

To check the speedo operation, put an electric drill on the input shaft and whirl away...

[brian]

I would have to borrow a modern drill as it needs to go anticlockwise......

[brian]

Also I have tried the heat-shrink plastic and it made no difference.
I do struggle to understand how the cable does rotate as I drive along with varying speed and with some force when I hold it as if the gearing etc were broken I would expect no movement.
I will see if I can lash up another Augusta/Aprilia/Aurelia speedo and see what happens!!!

[fay66]

For what it's worth most of the speedo drive gears I've ever seen have a square end which the flexible drive cable fits into, probably worth checking if  it is the same that the cable end still drives from the gear, I've also known composite drive gears, the gear itself is made of Nylon? that is mated to the shaft comes loose and although the gear moves it doesn't drive the flexible shaft.
brian
8227

[davidwheeler]

The cable drive gear in the gearbox is metal.  The driven end of the cable is a spade end as I recall and the speedo end is a square end of the modern type thin flexible inner.   Take off the cable and pull out the inner from the bottom which will show if it is broke or not!   You can drive the speedo input clockwise as there is an internal reversing gear to take account of driving backwards but don't go too fast!   If you fit the cable to the speedo and drive it from the gearbox end that will tell you if it is OK and then the problem would be in the gearbox drive or that the cable is not properly seated in the gearbox - there should only be a few mm of the brass collar showing and the spade/blade should be about 10mm long.   It can be fiddly to get it to engage but if the other end rotates strongly I guess that this end is OK.   It does sound as if something in the cable has broken, possibly the speedo end so that it is just too short properly to engage in the speedo input shaft. 

[brian]

Now I am really showing my mechanical ignorance here.
If I drive the speedometer from the back or by rotating the drive the wrong way ie as if in reverse do I see +ve MPH or does it stay still or show -ve MPH. As you can tell I have never really thought about this before.

I did start to look at the bits on the gearbox. The 90deg bit came off after I discovered the hole in the tunnel and although worn and rather sticky at some points works ok. I thought I would look for the bits inside the gearbox but I seem to have an awful lot to take off - 2 fabric joints have gone and the spider from the rear of the box but now it looks as if I need to take of the transverse rod (like the Augusta's) that locates the rear of the gearbox on the tunnel. True?
Going slowly as working above my head not good news for my multiply-operated-on shoulders!!!

All so I can see how far I have gone to the pub.............

[JohnMillham]

Now I am really showing my mechanical ignorance here.
If I drive the speedometer from the back or by rotating the drive the wrong way ie as if in reverse do I see +ve MPH or does it stay still or show -ve MPH. As you can tell I have never really thought about this before.

I did start to look at the bits on the gearbox. The 90deg bit came off after I discovered the hole in the tunnel and although worn and rather sticky at some points works ok. I thought I would look for the bits inside the gearbox but I seem to have an awful lot to take off - 2 fabric joints have gone and the spider from the rear of the box but now it looks as if I need to take of the transverse rod (like the Augusta's) that locates the rear of the gearbox on the tunnel. True?
Going slowly as working above my head not good news for my multiply-operated-on shoulders!!!

All so I can see how far I have gone to the pub.............

Not sure about the speedo, but the mileage will certainly be reduced if you turn the cable the wrong way - or, as I did many years ago with Peter Elias after making a navigational error on a rally where the distance travelled was important, reverse the car to reduce the mileage. We went backwards for some miles and won the event!
Regards, John

[SanRemo78]

If speedo design hasn't changed since pre war up to the 70's then it won't so any harm. The cable drives a magnet within the speedo head that rotates in a metal cup that's attached to the speedo needle. It's damped/restricted by a watch type spring and probably has a needle stop as a rest.

Guy

[davidwheeler]

Speedos work just as well in reverse as in forward, there is a reversing gear for the purpose!  However, the milometer does go backwards which is how cars were "clocked" by the unscrupulous - not possible with modern electronic ones.

[Tony Stephens]

Not entirely correct, David.
Jaeger Suisse and Jaeger Paris chronometric speedometers, as fitted to Lambdas, Bugattis and other quality cars, do operate in reverse (as do rev counters), there is a rocking gear assembly at the input drive which ensures this. Geared mileage and trip counters will count backwards, but most counters after about 1925 were ratchet driven which prevents reversing.
British Jaeger chronometrics, made by Smiths,do not have the rocking gear, and therefore were supplied in clockwise or anticlockwise form. These do not operate in reverse.
All magnetic speedometers are directional, and the nature of the movement, with a hairspring under the needle, and a zero stop, would prevent reverse indication. Without exception (as far as I know) all magnetics have ratchet operated mileage counters.

[brian]

Saga ongoing...
I have now got a drill that can go backwards so I put the cable on the instrument and apparently I went 30MPH!! I then put the spade end in the 90 degree bit and the instrument end went round when I twisted the spiral gear.
SO - problem IS in the back of the gearbox and I DO have to take off the cross-bearer etc.
Ah well..............

[davidwheeler]

Not entirely correct, David.
Jaeger Suisse and Jaeger Paris chronometric speedometers, as fitted to Lambdas, Bugattis and other quality cars, do operate in reverse (as do rev counters), there is a rocking gear assembly at the input drive which ensures this. Geared mileage and trip counters will count backwards, but most counters after about 1925 were ratchet driven which prevents reversing.
British Jaeger chronometrics, made by Smiths,do not have the rocking gear, and therefore were supplied in clockwise or anticlockwise form. These do not operate in reverse.
All magnetic speedometers are directional, and the nature of the movement, with a hairspring under the needle, and a zero stop, would prevent reverse indication. Without exception (as far as I know) all magnetics have ratchet operated mileage counters.

Fair enough, I have never drven my Aprilia backwards at any speed as the worn gears sound horrid.   I have taken apart many a Jaeger speedo though.