Odometer works properly but speedometer works intermittently?

This problem was noticed by my customer on his Ford Escort vehicle.

While driving the vehicle ,he noticed that odometer shows proper reading,but speedometer not showing correct reading.
After few minutes,the speedometer reading suddenly gets to normal and shows proper reading.

But this issue never stops,it again shows improper reading.

On that basis the possibility to be tried is as follows :-----

The problem you are describing is caused by a failing speedometer, if the odometer is reading correctely then its not going to be a speed sensor issue because the speedometer and odometer are one assembly and only serviced as one unit. To correct this problem you will need remove the speedometer/odometer assembly and send it out for repair.

There is online site who deals in repairing speedometer and odometers of ford and other branded vehicle.
The link is as follows:---

http://www.instrumentclusters.com/

This details will help.
Thanks.

Also see latest solved car problems :----

ABS & Brake lights warning indicator steady on dash and speedometer not working for Dodge Ram?

http://howtobyme.blogspot.com/2011/11/abs-brake-lights-warning-indicator.html

Isuzu rodeo speedometer is jumping?

http://schematicsdiagram.blogspot.com/2012/01/isuzu-rodeo-speedometer-is-jumping.html

How odometer works in cars?

http://technoanswers.blogspot.com/2011/11/how-odometer-works-in-cars.html

How to trouble shoot speedometer?

http://schematicsdiagram.blogspot.com/2011/06/speedometer-not-working.html

1996 fiat bravo speedometer not working?

http://technoanswers.blogspot.com/2012/01/1996-fiat-bravo-speedometer-not-working.html

Speedometer runs backward?

http://technoanswers.blogspot.com/2012/01/speedometer-runs-backward.html

Warning lights on and speedometer died?

http://howtobyme.blogspot.com/2011/08/warning-lights-on-and-speedometer-died.html

ABS & Brake lights warning indicator steady on dash and speedometer not working for Dodge Ram?

http://howtobyme.blogspot.com/2011/11/abs-brake-lights-warning-indicator.html

Vehicles Cluster panel Not reading Miles?

http://schematicsdiagram.blogspot.com/2011/12/vehicles-cluster-panel-not-reading.html