[T3] Brake Bleeding

Jim Adney jadney at VWType3.org
Sun Apr 17 15:57:16 PDT 2016


On 17 Apr 2016 at 20:12, J. Jonik wrote:

> 71 Sqbk:   Brakes got to need several foot pumps to work best.Jjust to
> make sure things were tidy, I made sure rear brake pads were good
> thickness, and adjusted.  Put a bit more brake fluid in the reservoir,
> and began a bleed job with a friend on the pedal. Right rear valve
> produced just a tiny spurt of air, then just drips despite brake pedal
> being pushed down hard. Left rear....just drips, also with no
> squirt.   Front right, same thing.   Front left, however, squirted
> like it's supposed to.

Make sure the reservoir is not actually empty on one (the rear) side.

Make SURE all 4 rear shoes are adjusted. If even ONE of them doesn't 
come up hard against the drum, there is no way for pressure to build 
in the rear circuit.   

It's probably bad hoses, but check to make sure the bleed valves are 
not plugged themselves. Take them all the way out and see if this 
helps. Wiggle a small wire down the hole to make sure there's nothing 
inside blocking anything.

If that doesn't fix it, loosen a connection upstream of the hose and 
see if fluid squirts out there. If so, the hose is the problem. It's 
common for the front hoses to fail. Rear hoses fail less often, but 
it happens.

I carry ALL the brake hoses for Type 3s, including the correct IRS 
right rear that no one else has.  

> So....is this hard evidence of Master Cylinder trouble?     It can't
> be, can it, that three out of four of the rubber brake lines going to
> the wheels all clogged up around the same time.About a year (?) ago I
> had to replace one of the front brake lines that was clogged solid. 
> That was probably the one that worked well today.  Are the others just
> catching up? 

This is probably not an MC problem, since you KNOW that the front 
circuit, at the very least, is working correctly.

> Then, IF it's the Master Cylinder...I have over half a dozen of them
> in my brake box.  All came from cars where they worked at the time the
> parts were taken.   Is it likely that they won't work after being dry
> and idle for years? 

There is 0% chance that an MC stored for a few years with brake fluid 
in it, will be an improvement. There is ~30% chance that such an MC 
is rebuildable. Stored like that, the bores will all be rusty.

Standard DoT 3 or 4 brake fluid absorbs moisture out of the air, even 
just sitting in the car. That's why you should always buy a new can 
of brake fluid when you add fluid. Fluid from an open can will 
already be moisture laden. Moist fluid boils at a lower temp and 
tends to promote corrosion of the metal parts that are exposed to it, 
like your MC and wheel cylinder bores. I recommend DoT-5 Silicone 
brake fluid, because it does not have this problem.  

If you don't want to bother with DoT-5, you should flush fresh fluid 
thru your system every few years. Pump and flush until you see new, 
clean fluid come out of all 4 wheels.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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