Speedo needle drops back down to zero

[e_londonvillage]

Evening all
I have owned my cc from new, 12 years, and recently within the last month, the speedo needle drops down to zero and then comes back to life and reads the speed that I am doing. This happens for a short time or for about 5 minutes. It works prefectly for about 98% of the time.
It usually happens when the roads are wet and yesterday when I jet washed the wheel arches. But worked after about 4 miles of driving. I also noticed that the journey I made yesterday evening was a fraction under 11 miles one way and about 7 on the way back. The car has done about 89k miles
Any help would be very much appricated as I have had this car from new and I don't like it when things play up.
Thank you
david

[GrandadMonkey]

The front wheel sensor normally has a protective shield over it (but not always). You'll find it behind the brake disc. If a protective cover is fitted under the retaining nut and remove it. You'll then see the sensor. If it is wet in there dry it out and dry off the cover too. Ensure the mating surfaces of the sensor and swivel hub are clean and apply a little grease to the sensor body to help keep out the damp (Esso Norva 275) and take it easy with the power washer down there in future. Make sure the sensor tip is clean and refit the protective shield and securely tighten its bolts.

If it still doesn't work properly then it may be that corrosion has set in and you'll probably need a new sensor.

Good luck.

[e_londonvillage]

GrandadMonkey
Top answer. I shall take a look and see what is going on behind the brake disk. Can you tell me which side I should be looking at NS or OS. Might save me 50% in looking time.
Cheers
David

[Capncol]

I think at your cars age the speedo sensor may be in the gearbox.
Look at the top rear of gearbox above drivers side driveshaft and if you can see a plug with an electrical connection, that will be the speedo drive. They suffer corrosion on the pins.