Can I fit an MTB freewheel onto my road bike? I am looking to replace  my 7 speed 12-18t freewheel on my old road bike to a different 7 speed (something like 14-28t) for easier hill climbs. 

Is it possible to do so and what are some possible problems I might encounter while doing this?

I found some 7 speed freewheels online and they are all advertised for mountain bikes. Can I fit one onto my old road bike? How do I know if the derailleur will still work and the sprockets aren’t too big for it?

My derailleur is an EXAGE 300EX.

Thank you
Most freewheels use the ISO standard thread and are interchangeable. Some hubs have a 'British' or 'Italian' thread which are very slightly different but still interchangeable. See the Sheldon Brown page on freewheels.

I don't know where to look up the specs of older Shimano derailleurs. Googling for examples for sale on EBay etc. and looking for specs included in the product description suggests:


Min sprocket: 12t
Max sprocket: 28t
Total capacity: 28T 


So you should be good with a 14-28 freewheel.