Front caliper seized, how to rebuild master cylinder?

Brake systems should only be cleaned with a proper brake cleaning fluid or clean brake fluid.
Anything else can contaminate the metal.
Don't use carb cleaner - it ain't a carb!

Gee, sorry...

Skip that part and do the rest...

I forget if I sprayed the bare reservoir out with the brake cleaner spray after washing them out completely. The carb cleaner is an acid base, but compatible with all the plastic and "rubber" bits in a carb, so it needs washed out completely after use. Next time I do it I will make sure to remember to make sure to clean it again with the contact cleaner. I sure don't regret using the carb cleaner since it did such a great job of cleaning all the surfaces of all crud.

yep sounds like a blockage.

another trick to finish off bleeding is to tie the brake lever "on" and leave it over night

Well,from the pics that new piston is trash.Where is the missing rubber?

Probably got ripped inserting the piston.Ripped against the circlip groove?

New piston.....making sure neither ports are plugged,no sharp edge at the circlip groove and some red rubber grease for reassembly!

A damaged seal will do what you are describing. The seal called B in post #53 has to be perfect. If it leaks even a bit it will leak like crazy when the whole system is properly bled, and you will not be able to exert pressure on the fluid. It will not leak when the MC is not connected to the lines. The leaking won't be visible at any time, because it's internal. Just like a leaky valve in your heart, the pump won't be able to create and sustain pressure on the fluid.

Sorry for the late replies, was traveling for work for the past 2 weeks so the bike just sat there but now I'm ready to tackle this issue again.

To recap: caliper was rebuilt and new pads installed by a shop. I rebuilt the master cylinder using a kit, replaced the brake line, and tried bleeding the fluid.

I can bleed the mc separately, I can bleed via the caliper only if I unbolt the brake line at the mc. Otherwise, once everything in buttoned back up I can no longer bleed the system (usual way nor reverse bleed).

The issue seems to stem from the mc but I have no clue what else I can do now.

If nothing better comes to mind, try the previous suggestions of post #56.
It is important to determine either or not the fluid is free to return all the way to the reservoir in the MC.

When I try bleeding the brake I can't seem to build up any pressure in the lever. When I reverse bleed I can't force any fluid into the caliper at all (using a giant syringe) BUT once I disconnect the brake hose at the MC I can reverse bleed the fluid right up to the banjo bolt. This says there is something clogged in the mc that won't allow fluid in.

Weird thing is, I can bleed just the mc (no hose) just fine, pressure builds up when I cover the hole with my thumb and even fluid squirts out.

Could be that the piston in your mc does not fully return, could be caused by misadjustment or something else.

Here is my thoughts

New kit for MC and caliper rebuild

Verify the hose and fittings are not blocked


When you reassemble the caliper
Pour brake fluid into the cylinder
Then reinsert the pistons; basically pre bleeding the caliper
Use a syringe and fill the brake line
Just before attaching to caliper
Then connect to MC

Then bleed as normal.