master cylinder

We're going to take a master cylinder off a wrecked 94 safari and put it on a 92 GMC full size van. Since this master cylinder is used, does it have to be bench bled, or can we just bleed all 4 bleeder valves? How
do you bench bleed it anyway?
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As long as the wrecked vehicle was not on its top (the reservoir full of fluid) it should not need to be bench bled. You will probably need to bleed all four bleeder valves, but sometimes as long as the system did not have air in it from the old master cylinder it may just work. I've had a little air work out on its own after a couple of days.

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Years ago when I actually took courses in this sort of thing, you just chocked it up in a vise, filled the cannister with fluid and actuated the plunger manually until fluid had fully circulated out of the master cylinder. You could use small lengths of curved brake tubing attached to the outlets of the master cylinder and bent so that the brake fluid was returned to the cannister.
I would do this if I were not sure that the fluid in the master cylinder were clean. You dont want any water or particulates going into your brake system.
But even then, we would fully bleed and purge the system after the cylinder is installed.
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