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Tear down of the brake master cylinder


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I have two master cylinders that need to be rebuilt. I already have the kits, and have done this rebuild before, but getting the piston out is always a problem. Yes, the circlip and the pin in the forward port have been removed. I suspect that it might be an issue with the fluid absorbing moisture from the air, and when it leaks and dries out, it prevents removal. With a rebuild master cylinder running about $300 with shipping (SJ is $240, shipping to Florida, and I have to send a core there first), and I need two of them, it is worth some effort to try to rebuild these myself. Shops do it. I can't can't figure out to get the flippin'g piston out.

Here is what I've tried so far:

1. Soaked it in penetrating oil. Also soaked it in acetone for 24 hours.

2. Blowing it out with 120 psi compressed air. The problem is closing off the top inlet ports, since there are no threads on there.

3. 20 minutes in a 110 deg F ultrasonic cleaner.

4. Banging it on the shop vise, with the piston pointed down.

5. Inserting a lead concrete anchor in, threading a screw in, clamping locking pliers on, and hitting that with a hammer. That has worked in the past, but not this time.

6. Connected a grease gun to it. That got the piston part way out, enough to get the first white and rubber washers off. The problem with that was that it is impossible to block off the top inlet ports. I tried using C/G clamps or my shop vise, but that is usually where the grease leaked out.

7. I opted NOT to use another brake master cylinder to apply pressure, as I thought that the grease guns were supposed to apply more pressure. I was also worried that brake fluid at 1000 psi would potential shoot things all over the garage, spraying everything in sight with brake fluid.

I'll probably go check with a local NAPA parts and shop tomorrow, to see if they have any ideas, or can do it for me.

Any other bright ideas?

A blow torch is out of the question. There are plastic parts in there not part of the rebuild kit. o easy way to clamp onto the tube without crushing it.

 

IMG_6732.JPG

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Maybe a dumb suck-eggs question, but you don't perchance have a piston stop pin in there, do you?

British Fart to Florida, Nude to New York, Dunce to Denmark, Numpty to Newfoundland.  And Shitfaced Silly Sod to Sweden.

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Then if the sum of what you've done won't shift it, I'd think it might need more than a repair kit.

British Fart to Florida, Nude to New York, Dunce to Denmark, Numpty to Newfoundland.  And Shitfaced Silly Sod to Sweden.

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Looks exasperating.  I'm wondering if the penetrating oil / acetone soak might have swollen the rubber/plastic bits and added to it's reluctance? If the piston can be forced a bit back into the bore, you might try chamfering the circlip groove a bit, or lightly polishing that portion of the (non-piston sealing) outer bore. Flatting the upper ports on sandpaper on glass, or running a flat file over them, might help seal the grease in, perhaps with a gasket of some sort in the vise.

 

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The correct answer is to boil it in water for an hour or so, and use an expanding concrete anchor inside the tube to extract it out. I have used the old lead shield type anchor before, and have usually been successful. I have a difficult one, so I haven 8 mm expanding concrete anchor on order, which should be here tomorrow.

41gi%2B82fETL._SY90_.jpg

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I would try a couple of G clamps with a rubber seal to close of the inlet ports and then apply pressure on the threaded brake line  ports with grease or a brake master cylinder.  As long as no air trapped in the system no chance of parts flying around but wrap it in a heavy cloth to absorb any flying bits if worried. 

 

cheers

Rohan

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18 hours ago, bgalbraith said:

The correct answer is to boil it in water for an hour or so, and use an expanding concrete anchor inside the tube to extract it out. I have used the old lead shield type anchor before, and have usually been successful. I have a difficult one, so I haven 8 mm expanding concrete anchor on order, which should be here tomorrow.

41gi%2B82fETL._SY90_.jpg

like that one, nice trick, I may use that sometime

 

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