Rear brake issues... piston seized? Or not enough pressure?

[AC_Schnitzel]

Went to change my pads -- it took a lot of force to push the piston back in. More than what I think would be normal.

Upon reassembly, I added new fluid and bled the line for any air that might have gotten in.

Pressing the brake lever, the piston doesn't move outwards at all...

Is my piston seized? Or am I somehow not maintaining pressure in the master cylinder?

[34nineteen]

You probably still have air in the piston. Hydraulic force through those braided brake lines should easily push the cylinder OUT.

Did you clean off the piston when you had it apart? Most every XB I’ve owned has sticky pistons, especially up front.

[AC_Schnitzel]

You probably still have air in the piston. Hydraulic force through those braided brake lines should easily push the cylinder OUT.

Did you clean off the piston when you had it apart? Most every XB I’ve owned has sticky pistons, especially up front.

Nah -- I just pushed it back in. Now the pedal isn't pushing the piston back out.

I don't have a compressor or grease gun -- how else could I get it out?

[34nineteen]

Is the lever going to the bar? If yes, then you have an air bubble. Keep bleeding.

If not, then something is stuck.
You could always take it to a bicycle shop and ask them to blow it out with compressed air. Usually they are easier with that sort of stuff than an auto/mc garage. Make sure to stuff a shop rag in there the pads go to catch the piston and make sure it doesn’t damage anything when it comes flying out at high speed.

Or I will sell you mine for $20 + shipping

[AC_Schnitzel]

St Paul HD doesn't have a rebuild kit for the rear caliper... Anybody know an equivalent part number for the Nissin assembly?

[34nineteen]

St Paul HD doesn't have a rebuild kit for the rear caliper... Anybody know an equivalent part number for the Nissin assembly?

How were you planning on rebuilding it, if you can’t remove the piston?

[AC_Schnitzel]

How were you planning on rebuilding it, if you can’t remove the piston?

My neighbor has a compressor -- might ask him if I can use it to push the piston out.

I'm also going to rebuild my rear MC first and see if that fixes the issue.

[34nineteen]

My neighbor has a compressor -- might ask him if I can use it to push the piston out.

I'm also going to rebuild my rear MC first and see if that fixes the issue.

Wait? So the master cylinder isn’t working? Why are you messing with the caliper if the master cylinder isn’t working? Or are you just guessi.... ohhhh never mind.... i get it now. Maybe try a TPS reset while you’re at it?

[AC_Schnitzel]

My question still remains. How do I discern between failing MC vs seized/corroded caliper piston.

Symptoms:
- brake lever doesn't build enough pressure to push piston out (though it can push fluid through the bleeder)
- caliper piston was difficult to retract (reservoir was off)

I took the entire assembly off the bike and will rebuild both since the parts are relatively cheap.

You asked for the part number for the assembly, not a rebuild kit.

My mistake, I meant the rebuild kit for that model caliper (not available w/ them).

EDIT: I will try to bleed one more time -- maybe there is air stuck at the top of the brake line near the MC.

[34nineteen]

St Paul HD doesn't have a rebuild kit for the rear caliper... Anybody know an equivalent part number for the Nissin assembly?

You probably should take your bike to a shop. This is all over your head.

https://st-paul-harley-davidson-buel...2010-xb-models