Thanks Tsuneo for all your help ,
Today again i tested with another 'Ferrite magnet' from another motor and luckily i got it working. i just found out that i have to piont exactly to the suspectible poistion which is in the lower region of the sonsor. but i have to be too close (less than 1.5mm), i'll need atleast a 5mm spacing between the shaft and the sensor to avoid accidental contact.i'll have to look for those cylinrical magnets mentioned here which seems more powerfull.

As i did said , i want to put 2 or 4 magnets on the shaft to have better feedback specially on lower RPM's.in my opinion these 2 magnets - or better using 4 N-S-N-S magnets - should be placed exactly in the mid or quarter position on the shaft circumfrence to have equal delays per magnet to magnet. if they donot position correctly, there should be some sort of processing to correct the over/under reading , this correction is possible in higher RPM's , not in lower RPM's which shaft is turning at lower than 60 RPM's(1 turn per second).i'm serouis to add more than 1 sensor , because in my perivous porject i've had strange problems measuring lower than 30 RPM's (.5 turn/second) do you professionals also have had problems measuring low rpm's with just single sensor as the encoder ?

About using the OptoCounter (Infra Red) i have had used them in some projects before and they're great, i could print my black/white shaft encoder easily with maximum possible accuracy. but this one is for measuring the Car's speed and the snesors got to be placed on the GearBox exit Shaft , which is Oily! and this could block the InraRed light.but Oil shouldn't have much influence on the magnetic flux.correct me if i'm wrong.