Clean them.
I'd avoid using any sort of solvent, as it would be bad for the pads and might simply make things worse.
First undo the noodle so you can access the face of the pads, then wipe pads and rims thoroughly.
Scrub pads and rims with a dab of detergent on a rag, then hose down to remove the detergent.
Reattach noodle.
(I always forget that part.)
The brakes will likely still be a bit "slippery", but riding with the brakes partially engaged for a minute or two should bring things back to normal.
bicycles.stackexchange.com/users/1584/Daniel R Hicks
Loosen the V-brakes, so you can access the pads (you can even remove them and clean each individually).
Then apply degreaser to them (there are many types
, I end up by using a citrus-type or in some more radical cases even use petroleum on the rim, but make sure you clean it with a rug afterwards!).
NOTE :
using a solvent or petroleum can damage some parts of your bike, so make sure you test it first and definitely don't use it on rubber!
Do the same to the rim.
Clean it very well with a rug and check if there is any trace of grease, if it has, try to degrease it further.
When everything is ok, just reassemble the brakes and test it, if you did everything correctly then it should work ok!
bicycles.stackexchange.com/users/1280/jackJoe
You should take the opportunity to give your wheels and brake pads a good clean.
A bucket of hot water with half a tablet of clothes washing powder and whatever brush you can find will do the job nicely.
Wash off with more water and the accumulated dirt on your rims plus the lube will be gone.
bicycles.stackexchange.com/users/1487/ʍǝɥʇɐɯ
My recommendation is to use a rag and de-greaser like Simple Green.
Apply the solution to your rag, wet pads let the liquid do its thing and wipe clean/dry.
If that does not work, repeat.
If after doing that twice you are not getting the appropriate braking power, I would gently sand the face of the brake pad with a fine grit sandpaper.
bicycles.stackexchange.com/users/1446/GuyZee
V-brake pads are rubber.
Degreaser can (but not always does) damage rubber.
use isopropyl alcohol.
It will remove the grease without damaging the rubber pads.
It may take multiple applications.
Clean the rims with it as well.
Quoting from Daniel's answer, with edits:
First undo the noodle so you can access the face of the pads, then wipe pads and rims thoroughly.
Scrub pads and rims with a isopropyl alcohol on a rag.
It will evaporate.
Repeat as required.
If more is required, sand the face of the brake pad with a fine grit sandpaper.
Reattach noodle.
(Everybody always forgets that part.)
Hope that helps.
bicycles.stackexchange.com/users/1259/zenbike
I'd use Simple Green or a similar mild degreaser followed by denatured alcohol to eliminate any residue.
Make sure and thoroughly rinse Simple Green off your rims and pads using water, it makes the brakes grabby, loud, and yet ineffective if you leave it on.
You could also lightly sand the brake pads to get rid of the contamination.
bicycles.stackexchange.com/users/15761/Eric
I accidentally got lube on my rear brake (v-brake) and my stopping power seems diminished. What is the best way to get it off the brake pads and the rims?
Removing lubricant from the rear brake and rim?
bicycles.stackexchange.com
<brakes><lubricant>
bicycles.stackexchange.com/questions/5176
bicycles.stackexchange.com/users/6/carl
Brake pads and rims can be cleaned with Simple Green and a cloth, isopropyl alcohol or washing detergent. Solvents should not be used as they may cause damage. The brake pads can also be lightly sanded to remove contamination. Strong solvents or petroleum can damage parts, especially rubber. Undo noodle to access the pads, clean pads and rims with simple green or another mild degreaser or detergent on the rims, then eliminate residue with denatured alcohol. Light sanding can also remove some residue.
Strong solvents or petroleum can damage parts, especially rubber, so clean with simple green or another mild degreaser or detergent on the rims, then eliminate residue with denatured alcohol. Undo the noodle to access the pads, then clean pads and rims before hosing down or clearing with denatured alcohol. Light sanding can also clear contamination.