Bouncing Speedo (occasionally no movement at all)

Noticed today that my speedo was bouncing eraticaly and then dropping to 0mph for most of my journey.
Ive had a quick look at cable connection into gearbox and there is a bit of play up and down if i pull the cable. Should it be tight with no movement at all? Ive not checked behind the dash yet for its connection in to mileometer.

I have had a bit of wiring work done (VDO Gauges, handbrake light, foglight), which could be coincidental but is there any electrical signal to the speedo needle or is it all just mechanical from the cable?

Any help greatly appreciated.

All mechanical. There shouldn't be any movement at the gearbox end, but I suspect its the cluster end that is the issue. Clips that hold it in can get brittle and if it has been knocked when wiring has been done that's the ilkley cause. If you can pull the stereo out you can reach in to the back of the speedo and make sure it is pushed home.

Thanks very much for the info, I'll take the stereo out and  have a look/feel to see if it's dropped out or loose. 
Will also try to tighten up the bracket that holds the cable into gearbox. 
Cheers! 

No movement on cable gearbox end so check the screw/bolt holding it in the gearbox is tight. You could be missing the gasket if you still have movement in the cable.

As mentioned check instrument cluster end.

No electrical stuff involved with the speedo drive.

So after a bit of interweb research it looks like I'm missing the gearbox seal and also the rubber washer that fits in it. Also looks like the metal bracket(the only bit I have) is fitted upside down! It's worked perfectly for last 10 years so still expect it's the connection to the cluster following the auto electrician doing his stuff. 

This website shows exactly what I'll need to order. Does anyone know the part code for the rubber washer? 

?????? ???????? ?? ??????. ????????? ????? ???????? ? ???????? ??????????. ? Volkswagen Golf Mk2, 1,8 ?, 1985 ???? | ?????? ?????? | DRIVE2

This should be the part you need https://www.classic-vw.co.uk/020-speedo-cable-to-gearbox-seal-171957861b-4991-p.asp

tnotty said

Thanks very much for the info, I'll take the stereo out and  have a look/feel to see if it's dropped out or loose.
Will also try to tighten up the bracket that holds the cable into gearbox.
Cheers!

NOOOOOOOOO.
The Better way is to remove the drivers side vent.  Worm your ARM the rear and re-connect it if it is loose.  Going through the Radio if you are not careful will result in breaking a Heater selector mount.  You have to remove the 2 screws holding the mount to allow it to float if not your forarm will break the mounting tabs hence my how to repair broken Heater control mounts in the Archive section.

https://www.volkswagenownersclub.com/threads/repair-a-broken-heater-control-mount-cabriolet.52938/?id=52938

Internally broken cables can momentarily cause the cable to catch and stop, then re-spin and bonce between them.
Going through the Side Vent is less bother some.

Right hand drive vs left hand drive. Speedo is on the right of the cluster, you'd need really long arms to get to it via the air vent of a RH drive car. Stereo is out of mine and that's how changed my speedo cable. I could put my arm in whilst driving and push it back in (clips had broken which is why I had to change it.)

J

As a third option I happened to have the knee pad/shelf thingy off for other work. If you then do some limbo/yoga and lie on your back with your head on the pedals (use a cushion) and legs up on the seat. Then you can look up under the dash and see the speedo. It’s still tight for your hands but better for me as I have big hands. Apparently


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Just a quick update. Speedo all back up and running as normal. It turned out to be a worn gear on the speedo cable. 
New gear fitted, Also replaced the top plastic bracket seal, the small 'O' ring and small snap ring(circlip)that sits in the collar on the cable and hold the gear on. (All of these parts were missing but the speedo had worked fine for the last 10years.!) 

Pic for reference (you can just see the small snap ring through hole in the gear)