Disk brakes severely reduced in power after replacing bearings so I am creating a few posts about bearings and wheels, (story so far):

how to reassemble mountain bike rear wheel hub and bearings

mountain bike freewheel hub stopped rotating

I have now got the wheels, bearings and freehub working.  Started riding to work this morning and I almost couldn't stop at a junction.  Thankfully wasn't going too fast.  I physically can not get the wheel to lock.  I have to use both brakes at full force to get the bike to roll to a stop.  If I only use one brake I would not stop at any junction in time.

Could the cause be any of the following:


Over greased bearings?
Over greased axle?
not tightened cone hubs enough?
not tighted axle enough?


I do not have any grease on the disk brakes them selves.  Rather nervous getting on the bike now.  Don't seem to be doing too well with this bike home fixing thing.

over greased bearings?

EDIT

Forgot to mention that it is hydraulic disk brakes.

EDIT 2

So in the end I took it to the LBS as I didn't have much confidence in my self at this point.  They had to replace the front pads but where able to clean the rear and cleaned the rotors.  (I had tried to clean the rotors but obviously not vigorously enough).  He said it was a bit of a pain to do.  All is working again.  They double checked my wheels and said I had put them back together correctly which is reassuring.

Thanks for all the help
If the brakes appear to be engaging fully then it sounds like you have some contamination on the rotors/pads.  I would clean the rotors throughly and replace the pads.  I have heard it is possible to bake contaminants off pads in the oven, and if you want to give that a shot google for it.