Listers,
Here is the text of the procedure which I used to bench bleed my master
cylinder after a recent rebuild. Excuse the intro prose but I thought it
would make more sense to include it for the eventual VTR archive. In
case anyone has concerns about the recirculation of the fluid, if you
don't do this, you will find that the fluid just keeps "falling through"
the MC as you do this. I suppose one could try to hold the "waste"
container into which the hoses will be inserted at a level where this
wouldn't happen but I didn't try that. Anyway, here is what I did:
Bench Bleeding a New or Rebuilt Brake Master Cylinder
After successfully rebuilding a master cylinder (or when fitting a new
one) it is a good idea to bench bleed the MC before installing it in the
car. This will fill the MC with fresh air-free fluid and in effect
"prime" it for integration with your car's hydraulic brake system.
The basic idea is to create mini hydraulic system on your bench. You
can use old brake line fittings if you have them but I didn't so I
purchased a master cylinder bleed kit from my local auto parts store. A
new MC may include the necessary parts already. The kit should consist
of a number of plastic fittings which are designed to fit in the outlets
(usually two, front and rear) of your MC. One end of the fittings will
be threaded and the other will have a round smooth hose adapter. Thread
the appropriate fittings into the outlets on your MC. The kit will also
contain a length of plastic hose. My kit had black hose but I found some
spare clear hose and used it instead - this will allow viewing of the
air bubbles passing through the hose. My kit also had a plastic clip
used to hold the two pieces of hose together and clamping to the edge of
the fluid reservoir.
Clamp the cylinder firmly in a bench vise so that the top is level.
Slide the hoses onto the fittings. Cut the hoses just long enough to
reach into the reservoirs and remain submerged - the shorter the length
of hose the better. Place the other ends of the hoses into the fluid
reservoirs (you'll probably have hold them in place somehow because once
you start pumping they'll want to flail around in the air and spray
brake fluid everywhere). If you can get a helper that is ideal.
Fill the reservoirs with new brake fluid, and pump the piston slowly and
evenly, full strokes. I used a big Phillips screwdriver because its tip
doesn't damage the piston
and the handle gives you something to lean against. I would not worry
about the fluid getting recirculated because it is brand new and you are
creating a temporary hydraulic circuit with the hoses which will not
become contaminated with dirt. The air which is still in the system at
this point will be bled out.
Pump the cylinder until the tubing contains no more air bubbles and no
new ones emerge from the MC on the down stroke. On my MC this took about
15 strokes some may require more, some less. Keep going until the air
stops as this will make the task of bleeding the brakes in the car much
simpler.
When all the air is out, mount the cylinder in the car. Here you have to
be careful to prevent the fluid still in the hoses from spaying your car
and any other painted objects nearby - brake fluid is a great paint
remover! If you decide to remove the hoses before installing on the car,
make sure to plug up the fittings - I just held the hoses up while
transferring from bench to car. Once the MC is mounted in the car,
remove the fittings and connect the brake lines. You'll lose a little
fluid but the check valves in the cylinder should stop any major
leakage.
Now you are ready to bleed the brakes in your car and it should be a lot
easier than if this step was avoided.
Peter Zaborski
76 TR6 (CF58310 UO)
Calgary AB Canada
-----Original Message-----
From: Ken Streeter [SMTP:streeter@sanders.com]
Sent: Monday, May 05, 1997 5:22 AM
To: Peter Zaborski
Subject: Re: Problems bleeding Spitfire brakes
Peter Zaborski wrote:
> Hello Ken Streeter:
> Is there any chance we can add a bit about bench bleeding then
MC to the
> brake bleeding article
(http://www.vtr.org/maintain/brake-bleeding.html)
> at the VTR site? I was using this article to assist me and
until I asked
> a mechanic here in Calgary I had no idea I was supposed to
bench bleed
> the MC, much less what bench bleeding is. I found a good
description at
Peter,
If you can write what you did on your TR6, it would make a
good addition to the article. Does everything in the note you
referred us to in dejanews apply to the TR6 master cylinder?
(It seems to me that one wouldn't want to "recycle" the brake
fluid through the M/C, unless it was brand new, and maybe not
even then, due to the likelihood of aeration.)
--ken
--
Kenneth B. Streeter | EMAIL: streeter@sanders.com
Sanders, PTP2-A001 |
PO Box 868 | Voice: (603) 885-9604
Nashua, NH 03061 | Fax: (603) 885-0631
|