Mark 9 brake master cylinder frustration


#1

hello
The brake master cylinder on my 1960 mark 9 is stuck!! the piston moved back in the bore when encouraged but will not come forward, I have tried compressed air and releasing agent but it wont budge, can I use a punch or small drift through the rear fitting and push it out or will i damage the spring that sits behind the piston?
thanks
bob


(Rob Reilly) #2

image
Looks like yes you can use a large diameter flat end punch and push it all through.


#3

Hey Rob
thanks for the reply, do you think that any of the parts before the piston will suffer if I punch through the rear opening?
cheers
bob


(tony) #4

item 4 is a long thin rod

is the opening you intend to punch thru a hydraulic port?

in the past, I have used the cars brake system to separate stuck brake parts, not sure where you are at with the car, but process would be refit master & resevoir, plug outlet ports ( with caliper bleed screws) …depress pedal, and pop piston out


(Rob Reilly) #5

Depending on how hard you have to hit the punch, try tapping lightly and probably you will see no damage or maybe just the rubber parts, which you are presumably going to replace anyway. Any harder and the long thin rod will bend, but you may be able to straighten it again or replace it.
Is the bore rusty?


#6

So the cylinder is on the bench and the rest of the hydraulic system is yet to be fitted so I can’t use hydraulic force to push it out yet

Light tapping through the rear fluid port has not resulted in any movement

If I go harder and bend the inner rod are they available??

Bore appears to be in good shape

Thanks


What to do with Old Gas
(Andrew Waugh) #7

Take a brake line fitting a tap it to take a grease zerk. Plug the other hydraulic ports. Fill the cylinder with water using a syringe, then thread your grease zerk fitting into the port. Put your grease gun on the zerk and pump until the piston comes out.


#8

Thanks Andrew I’ll give this a go!


(- 1950 MkV, 1959 XK150,) #9

That’s a clever idea of Andrew’s! it will be a slow controlled buildup of pressure, and no explosive decompression when it releases. (dont be tempted to use compressed air!)
The only minor comment I have is that If the water leaks past, then you may have to use all grease, rather than a mix of grease and water…


(tony) #10

Andrews idea will almost certainly work…if it wont, you are truly stuffed

however, I suspect the issue is the seals, especially if old, have “rolled” & jammed in there

if that is the situation, I would immerse the MC in boiling water for a fair while, lubricate with dishwashing liquid, and attempt to tap out the bore one last time…if that is easier for you than getting any needed fittings


(Andrew Waugh) #11

The water saves a bit of grease, making cleanup a bit easier, but mostly it speeds things up by reducing how many strokes you need to pump the grease gun.