Rear Brake issue!! - Sportbike Addicts

**John712** · 06-06-2009, 09:17 PM

If I leave my rear wheel on, I don't have a problem with rear brakes. But once I take the rear wheel off to either put the rains on, or get new rubber mounted and put the wheel back on, I pump the brake and get no pressure. I have to bleed the brakes to get pressure back.

Last night i went to IrocRobs house with my wheels and a new set of tires to get mounted. This morning I put them on, front had no issue after installing everything then pumping the brake and I got pressure in like 4 or 5 pulls.

Then I install the rear wheel, pump the brake and no pressure. Instead of bleeding the brakes, I took the lines off, blew them out, cleaned them all up so on and so fourth. I put it all back together, filled with brake fluid, pumped and bled and I got pressure. So for shits and giggles, I took the rear wheel back off then put it right back on, pumped the brake and no pressure. I had to bleed again. The rear brake does not have a reservoir but has a tube only (see pic below)

I was going to take the cap off the hose the 3rd time to see what happens but i got frustrated and said I got great pressure now, let me leave it befire me and the bike start rolling around on the garage floor out of anger. I'm at lightning tomorrow and didn't want to screw around anymore with it. But during the week I will try it with the cap off. But if I leave the wheel on, I have no issues.

RCM78 · 06-06-2009, 10:28 PM

sounds like the master cylinder is shot.

SPRHK · 06-06-2009, 10:55 PM

something is causing the MC to go airbound, or the seals are shot, but if that were the case, it wouldnt build up pressure after bleeding.

CBRBob · 06-07-2009, 05:29 AM

The resivour cannot be totally sealed, otherwise when you take the caliper off, the pads push back, the fluid goes up and when you try and draw it back into the m/c, it will create a vacum when you try and pump the brakes. The screw you have in there needs to let air in. Those hoses some people use are not a great idea as a res. If you are using one, it should be 8 inches long and only half filled when the brakes are good.