Z400 Rear Brake issues

[cubnfrank]

My rear brakes weren't working very well so I changed the pads. Even with the new pads they didn't work any better. For instance I apply the back brakes and the atv slows down but not quickly. I follow my friends on the trails and I see their back tires locked up and I can't stop as quick as them. I thought I had air in the lines. So I bled & bled the brakes. No change in stopping. Could my caliper be shot . It opens and closes it seems like it just doesn't clamp down on the rotor hard enough.
What may be the problem?

[Mars]

You have air in the line or you have a bad master cylinder.

1.Remove the cap on the master and stroke the rear brake lever, watch for air bubbles.

2.Stroke the rear brake lever a few times untill it is firm. Hold it down or have someone on the bike hold it down for one minute. If the pedal drops or you can roll the quad your loosing pressure. If nothing is leaking, rebuild your master cylinder.

[TRX450R_Racer]

Go to an auto parts store and buy a vacuum pump. (about $25) Put the hose on the bleeder screw open the bleeder screw and pump it down. The fluid will empty out quickly so make sure you have someone else fill up the master so it doesn't run dry. Do this until you see new clean fluid coming out. I would do the front and rear. It will do 2 things for you. One it will get all the air out and two it will replace the old fluid with new. I do this every year to my quad, street bike and truck. 

[cubnfrank]

Im going to check on that vacum pump.  I think it's a combination of problems with the master cylinder and air in the lines. Thanks