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I've searched around the internet, and according to what I've seen so far, the piston assembly should slide out once the circlip and stop bolt are removed, but I cannot get the secondary (rear) piston to come out. So far, I've removed the circlip, metal washer, and a rubber seal from the rear of the assembly, along with the stop bolt. There is a white plastic washer that is now exposed, but I haven't had any luck getting it to come out.

I've tried pulling the piston out by the shaft with a moderate amount of force, tapping around the outside of the cylinder with a soft mallet, and also tried driving it out from the front with compressed air, but none of these methods has worked.

The cylinder is relatively clean, with no rust, just dirty brake fluid, and the piston assembly moves freely when it's pushed in and released.

It feels like the piston or some other part is physically blocked by an edge or other surface within the cylinder.

Has anyone else experienced this? What was your solution?

Thanks -

The piston assembly was being blocked from removal by the white plastic washer mentioned previously.

The inside of this master cylinder is in very good shape, but the plastic washer sits over a groove that is machined into the cylinder, and this groove is open to the outside air by a vent hole that is drilled into the lower side of the cylinder casting, near the base where it bolts on to the brake booster. A small amount of rust had formed in this groove. The washer fits tightly into the bore, and there was just enough rust to wedge it into place.

I clamped a large socket into my vice in a vertical position, one that is larger than the outer cylinder bore but smaller than the mounting flange, with the fastener side of the socket facing up. The socket provides clearance for the piston shaft while the casting is tapped against it. I cleaned the exposed area of the cylinder and then repeatedly tapped the master cylinder against the socket until the washer and the rest of the assembly popped out.

In hindsight, it is odd that neither pulling on the piston nor the air pressure (120 psi) were able to drive the assembly out.

Glad you managed! Cylinder clean all the way to the end? I usually use a small honing tool to make sure the surface is perfectly even everywhere. Then fit fresh seals and refit the piston with enough brake grease. Very carefully, the seals damage easily!