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RE: [T3] Master cylinder question

<x-charset Windows-1252>The MC for disk brakes relieves all pressure to prevent the pads from
rubbing against the brake disk while driving.  In a drum brake system, there
are springs which cause the shoes to retract to their normal position.

Just as with wheel cylinders, the different manufacturers used different
designs for pistons and rubber pieces in the master cylinder.  For example,
I replaced an ATE wheel cylinder on my Beetle last summer with a NOS VW
wheel cylinder made by FAG and the piston design was completely different
despite being of the same size.

If it were my car, I would be using the master cylinder designed for the
type of brake system on my car.  The larger diameter master cylinder will
increase the amount of fluid pushed into the system when the brake pedal is
applied, so you should find the brakes slightly more touchy than they used
to be, but they will work.

Allyn de Vars
1962 and 1963 anthracite w/ pearl white T-34 Ghias
(2) 1967 pearl white Squarebacks
1984 Rabbit GTI
2001 Golf TDI
-----Original Message-----
From: Henrik Larsson [mailto:notchback@home.se]
Sent: Monday, November 12, 2001 12:21 PM
To: Type 3 mailing list
Subject: Re: [T3] Master cylinder question

Everett Barnes wrote:

>2. What's the difference between the 19.05 drum and disc brake master
>cylinder?  There appears to be no physical differences.  Internal valves?
I was researching this a year ago when I replaced the MC on my 1964
Notch. If I remember correctly the only difference between the 19 mm
drum and brake MCs is that the drum MC has a bottom valve that keeps a
little pressure in the system all the time. The disc MC has another
bottom valve that releases the pressure completely from the system.

If this is correct (as usual I have my mauals at my parents house) you
could use the bottom valve from your old MC and transfer it into the new
MC. The manual also talks about two different brands of MCs, I guess ATE
and FAG, and tells the mechanic NOT to switch internal parts between
these two brands. This could be something to keep in mind.

>3. Should I disassemble and lubricate the NOS master cylinder with brake
>fluid before installation?  Both are in perfect external condition and the
>pistons moves smoothly when bench-tested..
I did not and that was probably not a good idea. The first times I
pressed the brake the pedal felt much harder than usual. This was
probably not too good for the old rubber parts in the MC. The MC has
been working good since then, though.

Henrik Larsson, Sweden
1964 and 1968 Notches

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