[T3] Brake failure ‘67 Fastback

[Jesse Hernandez]

Jim, I agree I need a better mechanic.  The first time it happened was during a heat wave and it was 106 degrees.  I will have it checked out and let you know.  Thanks 
Jesse 

Sent from my iPhone

> On Feb 11, 2018, at 11:06 PM, Jim Adney <jadney at vwtype3.org> wrote:
> 
>> On 11 Feb 2018 at 22:08, Jesse Hernandez wrote:
>> 
>> I lost brakes and brake fluid was coming out of the reservoir.  Pedal went all
>> the way to the floor.  After a short time I was able to get some brake pressure.
>> My mechanic was unable to duplicate the brake failure and was unable to
>> identify the cause of the problem.  He replaced the master cylinder and the
>> brakes worked fine.  This past weekend the brakes failed again while I was on
>> the freeway.  Fortunately I was able to reach the shoulder and use the handbrake
>> to stop.  The brake fluid was again coming out of the reservoir.  After a short
>> time I was able to get some brake pressure.  What should I be looking for as the
>> cause of the brake failure?
> 
> That's about as typical (and extreme) a brake failure as anyone ever 
> sees. At least one wheel brake is dragging all the time. This 
> overheated enough to boil the brake fluid in it. When the fluid 
> boiled, that left part of the system filled with vapor that was 
> easily compressed (so it was impossible to develop any pressure in 
> the system) making the pedal ineffective. When the fluid boiled, it 
> pushed the fluid above it out of the top of the reservoir.
> 
> Once things had time to cool down, the vapor condensed and you got 
> your brakes back.
> 
> The solution is to figure out which wheel (or wheels) is/are over 
> heating. It's not the fault of the master cylinder. You should be 
> able to drive the car a short distance with minimal intensional use 
> of the brakes and then check all 4 wheels to see which one is extra 
> hot; reach thru the slots in the wheels and touch the disk or drum. 
> Be careful, don't burn your finger; the bad disk/drum will be 
> extremely hot.
> 
> It IS possible that someone has misadjusted your brake pedal (or rust 
> is preventing it from returning all the way.) There should be a bit 
> of free play in the brake pedal when you move it by hand: It's 
> usually about 1/2" at the pedal, but the important thing is that 
> there needs to be SOME free play there.
> 
> If it's a front wheel, you either have a sticky piston in a caliper 
> that needs to be rebuilt or a hose that's collapsed inside and needs 
> to be replaced. If it's a rear, it could be a hose, or it could just 
> be that the shoes have been adjusted too tight, or the wheel cylinder 
> is sticking, and should be rebuilt.
> 
> This is a simple problem which you have described very clearly. Your 
> mechanic should have figured this out. You need a better mechanic.  
> 
> I rebuild calipers. If the problem is in the rear cylinder, the 
> easiest thing to do is to rebuild it right on the car. It's easy.  
> 
> -- 
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
> 
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