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i have a 59 pf coupe #1421. it has drum brakes and a dual circuit master cylinder. i cannot get it to work correctly. i am not a novice on brakes and have successfully rebuilt many of them in the past on other cars. this master cylinder has the seals for the front and rear sections not connected as they have been on every other dual circuit cylinder that i have ever seen or looked at in pictures. i am not convinced that it ever worked correctly even when new. when bleeding it it will pump fluid back into the other reservour and run it over. i am thinking there is another cylinder available which will work such as one for a similar aged alfa or lancia or fiat. it is an underfloor mounted unit. anybody know of a solution? my supplier doesnt have anything but a single circuit type.

tom walgamuth
 

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Tom,

Do you mean that there are 2 halves of the master cyl piston within the cyl, and they are not joined? I have come across this before - the front half "floats" in the fluid, so to speak. When all is OK it is effectively "linked" by the effectively incompressible hydaulic fluid. If the fluid in the "rear" circuit (between the 2 halves) sprinks a leak then the rear piston will move forward freely under foot pressure to close the gap & then re-instate braking to the front piston.

If this is the case, maybe the "rear" half needs to be bled first so that it then becomes a "sold" pressure platform for the "front" circuit. Note that by front & rear I mean the F & R halves of the cylinder, not necessarily the F & R wheels.
 

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pf master cyl.

thanks for the tip.

i suspect that i have done that already but i'm not positive, so i'll try again, probably. the car also has a pressure increaser to the fron t wheel circuit. it increases the pressure to the front wheel s by double. i was unable to buy a new one and the rebuild of it is not confidence indspiring. so i was hoping to buy a different cylinder that is stepped with two diameters one 3/4" and the other the present 1.25" so i can at the same time eleminate the pressure increaser.

any other ideas?

tom w
 
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