Larry Hoy wrote:
>
> I am redoing the brakes on my 1967 MGB vintage race car. I have been
> advised that it would be a good idea to flush my brake fluid.
>
> I will be changing the type of fluid I am using, the old fluid is an
> "unknown" and probably a mixture of many fluids. The new fluid is AP 550.
> While it is not necessary to flush the system it has been recommended to me
> that I do.
>
> Since the cost of the new replacement fluid is so great, is there a way to
> flush the system without wasting the new fluid? Or do I just keep moving
> fluid through the system until I believe most of the old fluid has been
> replaced by the new fluid?
Larry, here's my method of accomplishing this, for what it's worth:
1) Open all bleeder valves and gravity-drain brake fluid. (if you are
concerned about spilled fluid, use clear plastic flex tubing to catch
the fluid in a pan). If you are catching the fluid, after most has been
drained, open all bleeders at once. If you are concerned about residue,
pump some new fluid through the lines, opening each bleeder in turn,
starting from the furthest, to clear them of any residue, *then*
gravity-drain.
2) Close all bleeders.
3) Fill master cylinder with new fluid. Refill as necessary during the
next steps. Do not let the fluid get low in the master cylinder.
4) Affix clear plastic flex tubing onto bleeder that is furthest from
the master cylinder. The tube must be long enough to place the other end
in the master cylinder reservoir so that fluid is pumped from the master
cylinder, through the brake lines, through the bleeder, through the
tubing, back into the master cylinder reservoir.
5) Open the bleeder just enough to pass fluid without much pedal
pressure. If opened too much, air may be sucked into the system past the
bleeder threads on the pedal upstroke.
6) Carefully keeping the master cylinder reservoir filled, pump fluid
through the system until no air bubbles are coming through the clear
tube. This may take a surprisingly long time to complete, but it's worth
it.
7) Plug the bleeder end of the tube with a small tapered punch or lead
pencil. affix that end to the next bleeder. Repeat until no air is left
in system and all bleeders have been tapped.
8) When complete, drain the remaining fluid in the clear tubing into a
container and save it.
9) This last step may or may not be necessary. If the pedal is still not
hard, tap on all lines, slave cylinders, calipers, etc. with a small
hammer to unstick any remaining bubbles from lines and rebleed. If
*still* not hard, arrange pressure to be brought to bear on pedal
overnight. It takes more than just putting weight on the pedal; I prop
mine with a stick cut to just the right length. Not sure how this works,
but it almost always improves pedal hardness.
That's it: *Very* little wasted fluid; no air.
-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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