You, my friend, have a lot to learn (IMHO). You might be amazed at the
residues of junk that remain in your hydraulic system after a fluid
replacement. Ever hear of surface tension, and viscosity? Want an illustration
of how the stuff can cling? Fill a metal cup with any flavor brake fluid; DOT
3, 4, or 5; Empty the cup, and return a while later to see how much has
adhered to the sides. Well, it is many times worse with small diameter tubing.
Drain all your hydraulics. Blow the lines out with low pressure air. Refill
the system and bleed it. Think you got it cleaned out??? Do it again in a few
months and see what you get.
If this method is standard operating procedure on American cars, it explains a
number of things. Do yourself and those with whom you share the road a
life-saving favor. Call any or all manufacturers of brake fluid, tell them
your suggestion and ask how they feel about reuse of brake fluid. You'll hear
an emphatic " DON'T ! "
Don't count on seeing dirt in a "clear" plastic tube as someone pumps the
pedal. The fluid velocity is too high for anyone but Superman to see anything
less than the size of a golf ball sail by. Another purpose of changing the
fluid (DOT 3 & 4 only) is to deal with a well known drawback of those brake
fluids: they are hydrophilic; they attract water. Water in your brake lines
will corrode metal parts. The old fluid is contaminated with moisture and
particulates; get rid of it.
So, you've rebuilt many master cylinders but haven't noticed any tiny
orifices. That is truly frightening. They are there; if you haven't seen them,
you are not doing a very thorough job of rebuilding. What you are doing is
potentially dangerous. Because you have been doing something wrong for a long
time does not make it right; it makes it a bad habit that you should break. I
can provide photos of the interior of an MGA master cylinder, clearly showing
the orifices you doubt the existence of. If any MGA 1500 or 1600 listers want
to see it, along with instructions for a complete rebuild, you'll have to
e-mail me direct. Unfortunately, I do not have a comparable package for the
MGB.
The frequency with which you claim to do hydraulic fluid changes is
commendable. I guess your cars must certainly have among the cleanest
hydraulic systems in the world, and moisture in your brake lines is probably
held to a minimum. After all, how much moisture can collect in six months.
But. . . you are still wrong to use a fluid recirculation method, and even
worse to recommend it to others; only one itty bitty speck of dirt, or rust is
necessary to disable the brakes. Have pity on those with whom you share the
road.
Jim
Rocky Frisco wrote:
> James H. Nazarian wrote:
> >
> > Hi List,
> >
> > I received a general message today that relayed an idea for bleeding the
> > clutch slave cylinder. It seems the recipient was advised to run a tube
> > between the clutch slave cylinder nipple and the Master Cylinder lid,
> > and pump the hell out of the clutch. The idea sounds clever until you
> > realize that besides removing air, you will very likely pump a piece of
> > dirt into your MC that could result in you losing your brakes or clutch
> > at a most inopportune moment. I can assure everyone, it does not take
> > much of a speck of rust to block the replenishment orifice in the MC of
> > an MGA 1500/1600.
> >
> > NEVER REUSE BRAKE FLUID. Even if it is for the clutch. There are some
> > very small orifices in the hydraulic cylinders that can be obstructed by
> > some surprisingly tiny bits of dirt or rust. One of the listers told you
> > the correct procedure and proper sequence of tighten nipple, press
> > clutch, loosen nipple, tighten nipple, release clutch, etc. Follow his
> > instructions, and DON'T PUMP ANY FLUID BACK INTO THE MASTER CYLINDER:
> > DON'T!!!!!!!!!!!!!!!
> >
> > For safety reasons I feel obliged to alert the list. It is not done to
> > embarrass anyone. We are all here to learn from each other's
> > experiences, and to share our own knowledge. So it is with the best
> > intentions that I say, DO NOT PUMP FLUID BACK INTO YOUR MC. PLEASE!!!
>
> Let's name names. I, Rocky Frisco, said that's how I bleed my brakes and
> clutch, and have been doing it that way without problems. First I drain
> the lines entirely and then refill with new fluid. Where's this piece of
> dirt going to come from? If it's already in the brake lines, after
> draining completely and refilling (deosn't everybody do this?) I will
> see it coming through the clear plastic line. That's why I specified
> clear plastic line and watching what's coming through it, bubbles, etc.
>
> This procedure is standard operation to bleed and prepare American
> vehicle master cylinders and I've found it also works well when an
> English or German MC will sometimes not set up on its own. My method
> just adds the rest of the system. I've rebuilt lots of master cylinders,
> admittedly not every model used on LBC's, but many of them. I've not
> noted any tiny orifices that might cause the brakes or clutch to fail if
> blocked by a speck of dirt.
>
> I have *never* yet seen a British car get fully bled by using the pump,
> loosen, tighten, pump, loosen, tighten, pump, fill etc. etc. method
> loved so well by American mechanics. It always leaves some air in the
> system. The difference between this and a really air-free system is
> unmistakable. Besides the recirculating bleed, I also put pressure on
> the brake pedal overnight after renewing the fluid. Not completely sure
> why, but this hardens the pedal even more.
>
> My alternative bleeding method is tube-in-bottle, open bleeder, pump
> slowly until no more air is visible (somebody else keeping the MC full).
> This gets better results than the pump-up method, but still not as good
> as the recirculating method.
>
> I understand it's common for people to leave the brakes and clutch
> hydraulics alone until something breaks. Most owners won't pay any
> attention to the brakes until the pedal sinks toward the floor or they
> find a bad leak and fluid all over the driveway or they hear
> metal-to-metal when they stop. I renew the whole system, metal lines,
> flex lines, cylinders and all, at least once every five years and I
> drain and refill with fresh fluid when I do the prep for the season
> change in the fall and spring.
>
> Tapping on the cylinders and lines will almost always dislodge more air.
>
> Perhaps I erred in taking for granted nobody would pump old, dark,
> crappy fluid through a system. I don't recommend that inexperienced
> people service their brakes or steering anyway, too dangerous. This is
> something that should be left to or learned from a good mechanic.
>
> -Rock
> --
> Rocky, JJ Cale Band & Pratchett Books: http://www.rocky-frisco.com
> Rocky's Mini Cooper Page: http://www.geocities.com/MotorCity/6437/
> Mini Books: http://www.geocities.com/MotorCity/6437/rockboox.html
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