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Stuck brake master cylinder piston


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I've tried to unstick with an airline, to no avail. Read than a grease gun might work - but my gun won't fit over a hydraulic nipple (which is wider than a grease nipple), and a grease nipple's thread is too small for the cylinder's hydraulic port. Am I missing something?

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Hi Roger,

No, you're probably not missing anything and my opinion would be that if the piston is well and truly stuck, your master cylinder might be dead.

If you remove the cylinder from the car, a sharp "bang" downward on a bench (with the piston facing downwards, as if it could fall out under gravity) might get it out.  You can then inspect the bore etc. to see if it's salvageable - brake parts can get very sticky if unused over time, but that doesn't mean they can't be cleaned, resealed, etc. and made workable.

However, as it's brakes it might just be better to start over with a new one - better safe than sorry.

Cheers,

Tim

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My advice would be to get the original one refurbished. Past Parts can do it, they ream them, put a stainless steel sleeve in and then new seals - would be much better than buying a new repro one. 

 

Jeff

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20 hours ago, TorontoTim said:

If you remove the cylinder from the car, a sharp "bang" downward on a bench (with the piston facing downwards, as if it could fall out under gravity) might get it out.

+1 for that

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The grease gun works, make an adaptor by drilling / tapping a brake union to take a grease nipple...needs to be a strong adaptor...if the piston is really stuck you might be pumping to thousands of PSI. It's very safe as the grease is virtually incompressible, so when something pops the pressure drops to zero instantly and you are left with oozing grease. Better to do this and deal with the mess rather than risk damage by trying mechanical extraction methods.

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Perhaps connect it to the clutch hydraulic line at the slave cyl hose and pump the clutch pedal?

Have you taken the circlip that retains the push rod out?

Peter W

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  • 1 month later...

Eventually got it out using grease gun method, crikey what a mess!!! Anyway piston was corroded - almost all the chrome coating had come off. Bitten the bullet (or wallet rather) and bought a new one.......along with wheel cylinders, clutch master and slave cylinders. Shame you cant get new pistons, all the barrels were salvageable.

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I'm refitting the caliper seals in the TR6 and notice the profile of the gasket has one high inside diameter edge rather than a straight forward rectangular shape.   I'm thinking the higher edge goes inboard toward the brake fluid pressure, with the lower edge permitting in and out movement.  

Have I got this correct?

 

Thanks

Edited by stillreel
Typo / clarify
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