Bench Bleed?

Is it really necessary to bench-bleed a new master cylinder (dual
piston)?

"John Stafford" > wrote in message
...
>
> Is it really necessary to bench-bleed a new master cylinder (dual
> piston)?

nope...not at all... "bench bleeding" a remote reservoir mastercylinder is
a waste of time if you don't keep fluid lines hooked to it when you are done
"bench bleeding"(and plug the outlets)....by the time you get it from the
"bench" to the car and installed, the fluid has already begun running out of
the outlets and air makes it's way into the inlets.... I've never "bench"
bled a vw master cylinder, and never will..... wasted time and
unnecessary... My opinion, of course...<G>

John Stafford wrote:
> Is it really necessary to bench-bleed a new master cylinder (dual
> piston)?

If you're like me and don't trust the manufacturer to put together a
clean mc then you will want to take it apart and clean it. You don't
know how long that mc has sat on the shelf; it could have rust in it.
Secondly, and I haven't done any research on this, but do they put a
preservative paste on the rubber seals? If so, you would want to remove
the preservative before installing the mc. The mc has some small
orifices, so it's a good idea to find out at least once if those
orifices are clear. You don't want anything but clean brake fluid
flowing in and out of all five cylinders. Bottom line: the brakes are
the most important system in the car because you have to rely on them to
stop the car, so peace of mind is more important than saving the time
and hassle of giving the mc (and the wheel cylinders if they're new) a
cleaning.

A word of caution before you start. A master cylinder is under a lot of
spring pressure. When you pop off the clip that holds it all together
make sure you have a rag around the opening so that the contents don't
launch into space and bounce off the ceiling, wall, your face, etc.

You should change the brake fluid every two years. I think that's also a
good time to go through the entire system and take apart and clean all
of the cylinders. A quote from the Bentley manual: "change the brake
fluid in your VW every two years. Brake fluid tends to absorb moisture
from the air and after two years of service its water content may be
enough to make replacing of the brake fluid necessary. Water can
initiate corrosion in the system and may also cause the fluid to boil
when the brakes are used very hard." If there's corrosion in the system
it can eat holes in cylinder walls and possibly result in loss of brake
pressure, meaning the car won't stop like it's supposed to.

Like Joey said about himself, it's my opinion but it's an opinion I
formed pert near 30 years ago.

-- Randall

In article >,
Randall > wrote:

> John Stafford wrote:
> > Is it really necessary to bench-bleed a new master cylinder (dual
> > piston)?
>
> If you're like me and don't trust the manufacturer to put together a
> clean mc then you will want to take it apart and clean it. You don't
> know how long that mc has sat on the shelf; it could have rust in it.

It is blister-packed, coated with some kind of oils and has has no rust
on the exterior.

> A word of caution before you start. A master cylinder is under a lot of
> spring pressure. When you pop off the clip that holds it all together
> make sure you have a rag around the opening so that the contents don't
> launch into space and bounce off the ceiling, wall, your face, etc.

I am not about to take this thing apart.

> You should change the brake fluid every two years.

Duh. No way.

In article >,
"Joey Tribiani" > wrote:

> "John Stafford" > wrote in message
> ...
> >
> > Is it really necessary to bench-bleed a new master cylinder (dual
> > piston)?
>
> nope...not at all... "bench bleeding" a remote reservoir mastercylinder is
> a waste of time if you don't keep fluid lines hooked to it when you are done
> "bench bleeding"(and plug the outlets)....by the time you get it from the
> "bench" to the car and installed, the fluid has already begun running out of
> the outlets and air makes it's way into the inlets.... I've never "bench"
> bled a vw master cylinder, and never will..... wasted time and
> unnecessary... My opinion, of course...<G>

I thought as much. One of the more expensive solutions to bench-bleeding
is to fill a bucket with fresh brake fluid and just drop the friggin
master cylinder in there and exercise it a bit. Way too spendy for me to
even try. I do have a power bleeder and I'm not afraid to use it - at
least now after the good advice. Thanks.

I also have dipped some fluid into the brake switch orifices using a
toothpick. It seems to work.

Thanks for that, Chris!

John

"John Stafford" > wrote in message
...
> Thanks for that, Chris!
>
> John

John, Randall has some good advice if our parts were a bit crappier than
they are at this point.... if it is a cheapie chainstore rebuild, I could
see needing some extra attention, but I've even had decent luck with
those....

BTW, I prefer gravity bleeding to pressure bleeding... easy and effective...

In article >,
"Joey Tribiani" > wrote:

> "John Stafford" > wrote in message
> ...
> >
> > Is it really necessary to bench-bleed a new master cylinder (dual
> > piston)?
>
> nope...not at all... "bench bleeding" a remote reservoir mastercylinder is
> a waste of time if you don't keep fluid lines hooked to it when you are done
> "bench bleeding"(and plug the outlets)....by the time you get it from the
> "bench" to the car and installed, the fluid has already begun running out of
> the outlets and air makes it's way into the inlets.... I've never "bench"
> bled a vw master cylinder, and never will..... wasted time and
> unnecessary... My opinion, of course...<G>

I always wondered about replacing a m.c. brake light switch. won't it
like to be filled with fluid so the fluid does it's job of pushing on
the contacts w/o air getting in the way? being a closed end , how would
that pocket of air every release?
I have an inquiring mind, I guess.
--
Money! What a concept.

In article >,
VFW > wrote:

> In article >,
> "Joey Tribiani" > wrote:
>
> > "John Stafford" > wrote in message
> > ...
> > >
> > > Is it really necessary to bench-bleed a new master cylinder (dual
> > > piston)?
> >
> > nope...not at all... "bench bleeding" a remote reservoir mastercylinder
> > is
> > a waste of time if you don't keep fluid lines hooked to it when you are
> > done
> > "bench bleeding"(and plug the outlets)....by the time you get it from the
> > "bench" to the car and installed, the fluid has already begun running out
> > of
> > the outlets and air makes it's way into the inlets.... I've never "bench"
> > bled a vw master cylinder, and never will..... wasted time and
> > unnecessary... My opinion, of course...<G>
>
> I always wondered about replacing a m.c. brake light switch.

Ah, glad you asked. The old trick is to dip a slim toothpick in brake
fluid and insert it into the orifice. Another is to use a syringe and
needle to push a drop or two of fluid in there. I got lots of them as a
'side benefit' to home health care.

"VFW" > wrote in message
...
> In article >,
> "Joey Tribiani" > wrote:
>
>> "John Stafford" > wrote in message
>> ...
>> >
>> > Is it really necessary to bench-bleed a new master cylinder (dual
>> > piston)?
>>
>> nope...not at all... "bench bleeding" a remote reservoir mastercylinder
>> is
>> a waste of time if you don't keep fluid lines hooked to it when you are
>> done
>> "bench bleeding"(and plug the outlets)....by the time you get it from the
>> "bench" to the car and installed, the fluid has already begun running out
>> of
>> the outlets and air makes it's way into the inlets.... I've never "bench"
>> bled a vw master cylinder, and never will..... wasted time and
>> unnecessary... My opinion, of course...<G>
>
> I always wondered about replacing a m.c. brake light switch. won't it
> like to be filled with fluid so the fluid does it's job of pushing on
> the contacts w/o air getting in the way? being a closed end , how would
> that pocket of air every release?
> I have an inquiring mind, I guess.

although air is compressible, the switches need very little "pressure" to
make contact, and the pressure of the braking system is pretty substantial,
even with light braking... making sure that tiny orifice is full of fluid is
moot in my opinion...