Date: Mon, 15 Aug 2011 20:28:00 -0500
Reply-To: Tom Hargrave <thargrav@HIWAAY.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tom Hargrave <thargrav@HIWAAY.NET>
Subject: Re: is this MC rebuild kit for real?
In-Reply-To: <CAJDR84aKE1vMo=k7bXnCHt7ni4i7+p2JaQLASwREmq8B-+KigA@mail.gmail.com>
Content-Type: text/plain; charset="us-ascii"
If you hone the cylinder until it's too over sized then the seals won't seal
properly. Just remember, as you hone the cylinder you are removing metal and
the ID is slowly getting larger.
My "rule of thumb" was if I could feel the corrosion depression with my
finger it was trash because by the time I honed the cylinder enough to
remove the corrosion the cylinder was too large. But a lot of corrosion will
look like a light surface stain & when you run your finger over it you will
feel the roughness but no depth. These are easily honed out.
Also, sometimes you will disassemble a cylinder and see no corrosion at all
and these can be the toughest ones to decide to rebuild. And the reason why?
Remember all of that very dark brake fluid you drained? The dark color came
from iron & that iron was removed from the inside surface of your master
cylinder and wheel cylinders. In other words, everything may looks smooth &
perfect but it's not. Just because your master cylinder looks perfect does
not mean it has not been eroded to over size. The water dissolved in your
brake fluid & the oxygen it carried along has been eroding away at the
inside of your master cylinder.
The real enemy is your brake fluid. DOT3 brake fluid is hygroscopic which
means it loves to absorb moisture from the air & this is also why experts
tell you to only fill from a sealed container. A sealed container has not
started absorbing water yet while a open container that's been sitting on
your shelf for 2 years may be 100% saturated with water. You may be creating
a problem by filling from a open container!
There is a very simple & cheap solution to all of this. Use DOT4 brake fluid
and change it often to keep the water out. But how often? I can tell you
because a lot depends on local climate. But I can say that if your brake
fluid is turning dark you aren't changing it often enough. I pull out the
contents of the master cylinder of any car I'm working on and top off with
DOT4 and except for master cylinders on recent purchases, I have not
replaced one of my master cylinders in over 20 years.
The only one that has dark fluid is my 1977 Vette and no matter how often I
change what's in the reservoir the fluid turns dark. But GM cars of that era
have huge surface area compared to the fluid volume & I suspect the fluid is
absorbing water very fast. I also believe that changing the Vette master
cylinder is unavoidable.
Thanks, Tom Hargrave
www.stir-plate.com
www.towercooler.com
www.kegkits.com
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Robert Downes
Sent: Monday, August 15, 2011 7:13 PM
To: vanagon@gerry.vanagon.com
Subject: Re: is this MC rebuild kit for real?
Thanks for the reply, Tom. Am i correct that your implication is that if i
am not equipped to accurately hone my cylinder and order new seals
accordingly, then attempting a rebuild is likely folly?
And Ed, i do indeed have a proportioning valve. funny that it is not
mentioned by Bentley. had to do some research just to find where it's
mounted. I am , however, not sure that it failure would explain all of my
symptoms. also, the internet seems to generally go by rust on the valve body
to indicate condition, and mine is quite clean.
-bob
'83 transporter diesel L 1.6TD 5sp--"Kid Cassidy"
On Mon, Aug 15, 2011 at 1:05 PM, Tom Hargrave <thargrav@hiwaay.net> wrote:
> For most master cylinders you only need to know the bore size and the
shaft
> size. What gets replaced are the cup seals & the rear seal and they are a
> common design.
>
> The same is true for wheel cylinders - you only need the bore size.
>
> Whether or not a cylinder can be rebuilt depends on the extent of any
> corrosion & the final size the bore is honed to after removing the
> corrosion. Some are just not rebuildable.
>
> Your problem is probably going to be some corrosion letting fluid bypass
> one
> of the seals until the seal wipes past that spot.
>
> You'll also discover that even in metric cars, most bore sizes are in inch
> dimensions.
>
> Thanks, Tom Hargrave
> www.stir-plate.com
> www.towercooler.com
> www.kegkits.com
>
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
> Robert Downes
> Sent: Monday, August 15, 2011 9:27 AM
> To: vanagon@gerry.vanagon.com
> Subject: is this MC rebuild kit for real?
>
> first the question, then the story.
>
> i'm searching around for a master cylinder rebuild kit because i know they
> exist, and i've never been inside a MC before, and found
> this <https://www.rockauto.com/catalog/x,carcode,1286333,parttype,1840>.
> i am always skeptical of these all-parts-for-all-cars websites that list
> inventory from warehouse indexes, so i invoke the wisdom of the list: if
> these are appropriate, why cant i find them anywhere else? if not, does a
> kit exist?
>
> AND, why am i planning to get all up in dat MC you ask? well, i rebuilt
all
> my brakes mechanical-wise about 18 mos/20k miles back and they have never
> been perfect. when i hit the brakes fresh, the pedal sinks a bit deeper
> than
> it should, if i push hard it will bottom out(but i can still push harder
> for
> more braking force). if, however, i pump once, release, and then brake,
> they
> feel normal. ...and then after about 5 seconds the pedal falls into the
> usual routine.
> it has never felt close to dangerous, i have never lost a drop of fluid,
> the
> condition has never worsened.
>
> well, i was recently rotating tires and poking around a bit in prep for an
> upcoming round of shop time, and noticed this: my shoes are about gone,
and
> my pads look like they have not worn at all. is that normal? i remember
> buying the higher-end pads, and the rotors tell me that they're doing *
> something*, but they've a solid 1/2" of meat left. is this normal? i admit
> i
> only *assume* that it is not. the master cylinder is the last thing more
> complicated than a tube that i haven't replaced/renewed, so it's next.
>
> prove me wrong, friends!
>
> -bob
> '83 transporter diesel L 1.6TD 5sp--"Kid Cassidy"
> -----
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