Vivitar flash on Canon D60

..... I use a Vivitar 728AF flash for occasional stuff (usually use the
onboard flash for most things)on my Canon 300d... works well in Manual
up to 1/200 (max)..

When I put in on a Canon D60 the flash emitted is very low (not as
strong as the onboard flash) and the camera allows me to put the speed
up to anything i like (above 200) ???

although the flash fires it doesn't seem to be 'communicating' with
the camera... anyone know why ????

ps. Same on a friends Canon D30 - the flash fires but not very
strong...