hard break pedal

You have disc brakes so there's no adjustment issues, this sounds like the master cylinder may be failing. What you will want to do is drive it until the issue starts occurring then jack the sticking wheel up in the air, try to turn it and if it's dragging do this: find the brake line from that wheel that attaches to the master cylinder, break the line free for a split second, just to see if it relieves the brake pressure to that wheel. Do this for just a 1/2 second, until a little fluid comes out. See if the wheel spins freely, if it does I would say your master cylinder is bad. Using the wrong brake fluid can make this happen too so make sure you always use the correct type.

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