I posted this a while ago on the samba. Bench bleeding can be done in the car. You will need to make up solid plugs for each steel line on the master. This can be done using a brake line, cutting it about 2 inches from the nut and folding and brazing the cut end.
Bench bleeding is standard practice in high volume repair shops. It is a term used to describe bleeding the master separate from the rest of the braking system.
Many masters are designed in such a way {Step bore masters are nasty for this.} or positioned on the vehicle so air removal is almost impossible. This saves time and labor should you install one and find it did not fix the problem. Also keep in mind that most master cyl's are not as easy to change as the ACVW master.
Most masters have a resevoir built in. If the res is connected to the master and the cover sealed when installing the master on the car, there is no loss of fluid when the port plugs are removed to install the lines. As stated below masters with remote res should be bench bled on the car.
Also if the only thing being changed is the master on a previously working system then the bleeding is done at the ports on the master. The lines are simply cracked open {just like a bleeder screw} and any air escapes around the loosened line nut.
Although many people use the messy tube method I have used the following method for the last 20 years.
New and improved master cylinder bench bleeding procedure
www.cardone.com/english/club/products/brakes/protech/articles/Bleeder.aspThe most common problem customers face when installing master cylinders is improper bleeding procedures. In the past, CARDONE supplied a bleeder kit that consisted of plugs with holes. Tubes pressed on to the holes in order to bench bleed the master cylinder. Although this kit was successful when used properly, it was not the best process. One of our goals in Technical Services is to improve every process. We found a better way.
The new bleeder kit comes with solid plugs to bench bleed the replacement unit.The advantages of the new process are:
More efficient to bleed the master cylinder.
No mess or fluid dripping when bench bleeding or when installing the unit on the vehicle.
Proving the unit is functional during bench bleeding. If the piston is firm when bench bleeding and not on the vehicle when bleeding, the brake system is at fault, NOT THE MASTER CYLINDER.
The following process is supplied with each CARDONE replacement master cylinder. You can help our customers by stressing the importance of following every process we include with our parts, to prevent warranties and increase sales.
1) Transfer proportioning valves, switches or other components to the replacement master cylinder (as applicable).
2)
Tighten bleeder plugs into ports (bleeder plugs may be in parts kit or master cylinder reservoir).
3) Support the master cylinder in a vise in a level position. Never clamp onto the body of the master cylinder.
NOTE: Units with remote reservoirs should be bled on the vehicle. It is VERY IMPORTANT that the body of the master cylinder be kept level during the bleeding process.
4) Fill reservoirs halfway or until reservoir ports are covered. Always use new brake fluid from a sealed container as specified by the vehicle manufacturer.
5) Install reservoir lid so brake fluid does not spray from reservoir during bleeding process.
6) Using a blunt tool or dowel (brake pedal if mounted in vehicle), SLOWLY press in and release the master cylinder piston using short strokes of 3/4” to 1”. NEVER STROKE PISTON MORE THAN 1”. Repeat this step until resistance to piston movement is firm and less than 1/8”.
IMPORTANT NOTE: On step-bore master cylinders, WAIT 20 SECONDS BETWEEN STROKES. This will allow air trapped in the quick take-up valve to rise into reservoir. MASTER CYLINDER BODY MUST BE LEVEL.
7) Install master cylinder on vehicle. DO NOT remove bleeder plugs until brake lines are ready to be installed. This prevents air from entering the unit and brake fluid leaking out.
Cool Remove one bleeder plug at a time from the master cylinder and connect the proper brake line to that port. Repeat this step for remaining brake line ports. Be sure fluid level is maintained during installation of brake lines and that all fittings are clean before installation. Bleed brake system according to vehicle manufacturer’s procedures and specifications.
9) Verify proper pedal action before moving vehicle. Do not road test vehicle until correct pedal feel and travel are obtained.
NOTE: If firm brake pedal action results using bleeder plugs, but becomes soft after installation in vehicle, the problem is not the replacement master cylinder.
