Removing Stuck Master Cylinder Pistons

[UncleBoogie]

I'm quarantined and bored, so I thought I'd share. I got tired of fighting with stuck master cylinders and came up with a tool to get them out. Maybe there's already one out there, but I have more time than money so I tend to build stuff.
I cut the head off of a banjo bolt for a brake line and drilled the center out enough to tap it out for an alemite fitting. I screwed the alemite into cut end of the bolt and screwed the other end into the master cylinder. Then, I pushed the frozen piston out with a grease gun. I lost a little grease through the tiny holes in the reservoir, but it worked. It has worked several times, every time. I keep ths thing in the tool box now. If anyone knows a different way to this, I'd love to hear it. Any cool tricks for that matter.
Cheers!

[10mm Nut]

I consider stuck master cylinders similar to stuck engines. Often a good soak and patience is the order of the day. Lots of patience.

I did a particularly bad one awhile back. After soaking and cleaning I still couldn't get it to move. I wound up center drilling the piston and using a bolt extractor to get the piston to turn. As soon as it turned, the battle was won.



If that would have failed though, my next step would have been to hydraulic it out like you did.

[pidjones]

Grease gun is the way to go. No risk of damage to the bore by missing with the drill.

[10mm Nut]

I can't imagine how you'd goof up drilling the piston. It's got a huge dimple in the center of it to center the pushrod.

[UncleBoogie]

I can't imagine how you'd goof up drilling the piston. It's got a huge dimple in the center of it to center the pushrod.

You’d be amazed at what I can goof up.

[Track T 2411]

Nice! And the tool can also be used for those pesky caliper pistons...

[Sidecar Bob]

Great idea. I've never had a master cylinder that I thought was worth salvaging that I couldn't get the piston out of but I already have a short banjo bolt with a zerk fitting for getting pistons out of calipers so I'll try to remember this if I ever do come across one I want to rebuild.

[tomk1960]

I'm usually successful by doing the following:

Squirt a good penetrating oil down the bore to lubricate the stuck piston.
Drill a 1/8" hole partially down through the top of the piston.
Screw a sheet metal or drywall screw into the hole.

Grab the head of the screw and try pulling it out. Sometimes, the piston will break loose during the drilling process.

In really stubborn cases, I can pump out the piston with a spare front master cylinder. Hydraulic pressure works every time. Ironically, more times than not, when I get the piston out, I find the bore to be in excellent shape. Go figure!

[Sidecar Bob]

They are usually stuck because of corrosion outboard of the seals so everything inboard of there should be clean.

[Steven UK]

I just did the grease gun truck with my rear slave cylinder, worked wonderfully.

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