<VV> Brake Master Cylinder Question

[Jay Pitchford]

All,

Thank you for the quick responses and great advice. The improvement in
stopping power was instant and dramatic. I was pretty aggressive on
the fluid fill level, as I didn't leave much of any gap below the top
of the MC.

I noodled on the brake fluid loss as well, and looked around for
evidence. It looks like I've had a very slooooow leak at the back of
the MC for quite some time ... in fact, since I bought the car 2.5
years ago. Shame on me for not knowing to check and/or change the
fluid, given the hygroscopic nature of DOT3/4. I'm going to monitor
the MC level in the near term, and order a new MC once I've checked
elsewhere for fluid losses.

Again, thank you for ALL the responses I got, public and off-list. You
guys are wonderful!

jcp

On Fri, May 11, 2012 at 11:16 AM, J R Read <hmlinc at sbcglobal.net> wrote:
> Jay,
>
> DOT 3 or 3-4 is hygroscopic (sp?) (absorbs moisture from the air).  Water in
> the brake lines is NOT a good thing.  That rubber boot under the top of the
> MC is designed to expand to fill any void (to keep air out) should the fluid
> go low.  Fresh fluid should be added after removing the "cup" to as near
> full as you can get it without spilling any.  Put a rag below the MC to
> catch any spills since the brake fluid will eat the paint off of your trunk
> floor. Flatten the boot back out if it has been expanded when replacing it.
>
> Now...  why did you loose fluid?  It really does not evaporate - so there is
> very likely a leak someplace.  Check for leaks in the system.  Most common
> place for leaks is probably at wheel cylinders, but could be elsewhere. Look
> at the back side of all four wheels for dampness.  Also, check the toe panel
> in the passenger compartment for dampness as well - that would indicate a MC
> leak.
>
> Later, JR
>
>
> ----- Original Message ----- From: "Jay Pitchford" <jay.pitchford at gmail.com>
> To: "Virtual Vairs" <virtualvairs at corvair.org>
> Sent: Friday, May 11, 2012 8:53 AM
>
> Subject: <VV> Brake Master Cylinder Question
>
>
>> The master cylinder in my '65 Corsa convertible appears to be low on
>> fluid. I've purchased Valvoline synthetic DOT 3-4 brake fluid to add
>> some. My question is, do I add the fluid directly into the rubber cup
>> that's located inside the master cylinder, or do I lift it out and add
>> underneath? How much should fluid be in the master cylinder? Do I fill
>> it to the top?
>>
>> Jay Pitchford
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