what will happen if you lose the shunt field
on a dc shunt motor

I think it will overspeed. Generally, there is a field loss relay in series with the field that would open the control circuit if it were to drop out.

ok good because thats what i put on the exam.
i no a series motor will overspeed but i was not sure about a shunt thanks

If you oopen the field switch to a shunt motor if will take off and self-destruct, this is why they put a field-loss relay in the control circcuit to prevent this from happening.