<VV> Temporary loss of brakes when in reverse

[Jay]

Greetings,
    I have experienced perfect brakes, then all of a sudden the peddal goes 
to the floor!  Turned out, the mosture absorbed into the brake fluid, 
causes an accidic compound in the oil.   This eats away at the aluminum 
piston in the Master Cylinder.  When those little "holes" dinally break 
through - there is NO BRAKING!

    Mine had rotted through in my '66 Corsa 140, and late one evening while 
heading home the pedal went for the floor.  I rolled through a four-way 
intersection that lukily had no other cars in it!  The trip home (35 
miles) was done using my Emergency Brake.  Tore down the Master and found 
that the piston was swiss cheese!  Got a rebuild kit ASAP.

    If your peddal ever goes to the floor, best to replace the guts of the 
MC and be sure you, and others on the rode, as safe.

       --- Jay Nugent
           Ypsilanti, MI
           '64 Greenbrier


On Mon, 24 Aug 2026, Frank DuVal via VirtualVairs wrote:

> When the brake pedal goes to the floor with a light touch of the foot but it works fine with harder application,  it means the master cylinder needs rebuild/replace.
>
> This is for both single port and dual port master cylinders.
>
> Frank DuVal.
>
>> On Aug 24, 2026, at 7:33 AM, eric--- via VirtualVairs <virtualvairs at corvair.org> wrote:
>>
>> I had stopped in a parking lot with my '64 coupe 95hp PG running errands.
>> When I restarted the car and shifted into reverse the brake pedal went
>> straight to the floor. I was able to shift into forward and not run over the
>> pedestrian behind me. The brake pedal immediately regained pressure and the
>> brakes worked fine on my ride home. I do have brakes in both forward and
>> reverse.
>>
>> I have not seen any fluid leakage on the garage floor and have been too busy
>> to get it on the lift. It's a low mileage car (19K) and the PO had changed
>> the brake lines when he awoke it from a 40 slumber. Still has a single
>> master cylinder and it seems to be in great condition, maybe a little low on
>> fluid.
>>
>> Before I dig into this I'm looking for some clue as to why I had (for now) a
>> one-time loss of pedal pressure. I have not driven it since getting it home
>> that day.
>>
>>
>>
>> Eric
>>
>>
>>
>> --
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