So I have been riding and I have lost my back brake a couple times now. Each time it has happened I just pump it a bit and it stars working again but it has allmost caused me to crash each time it happened. I have no idea why it is doing this. Can someone please help I'm racing the powder mountain race that jeremy mcgrath puts on here every year and its s fast paced track and I really dont want this happening out there and ruining my weekend practice is thursday so I have to have this fixed. Its probably something simple but I'm fairly new to this sport and working on my own bike so I have no idea what to do.