Afternoon Gents,
I finally got around to changing out the MC on the 1990 240. Thanks Art, I adopted your suggested methodology of bench bleeding. It was a Cardone reman unit and it actually came with 2 lengths of clear plastic hose and two temporary plastic bleeders. I have bench bled until I felt no "squishing" of air bubbles in the cylinder nor seen any in the tubes. My question is primarily just one of curiosity, why could I not "bench bleed" again now while the bleeders are attached but the MC is attached to the booster? Or could I? Just now use the pedal and the actuator of the booster as is? Could that be done in general "on the vehicle"(in situ)? There should be no corrosion on inside of MC as its rebuilt, so no spots that typically dont get used to F up the seal...right?
Thoughts before I proceed?

I put her back together last night and did a quick bleed. Started her up and the pedal seems firm and high. I ran out of gas(mine) and didn't get her off blocks and wheels back on for test drive. Will do this afternoon.
That being said, next time I have to change a MC, the bench bleed will be done in the car. No reason not too.
Have a Happy!

I use a method similar to trev29--bleeding with the master mounted. I leave the lines disconnected and use rags to absorb the waste fluid. I use my fingers to cover the open ports and a helper to gently depress the the pedal. You can feel when the fluid has filled the master--there will be distinct pressure at first the port closest to mounting end and then the one farthest away. As the pedal is depressed you roll your finger off at the bottom to let fluid escape onto the rags--when air is bled out you will feel the pressure. It may take three or four or five pumps to get to that point for each port. When satisfied that air is out I quickly attach the lines. I've never had to re-bleed -- having done many, many masters. Flush the area with water when done. -- Dave

Yes.

The reason for the bench bleed seems to be to avoid spilled brake fluid which could cause paint damage. Brake fluid is pretty cheap so it is not likely because of cost.

After a bench bleed, if the pedal drops to the floor then there likely is still air in the MC. Rather than pull the MC and bench bleed again...
-crack open the ports at the MC
-depress brake pedal so fluid (and air) is expelled past the "cracks"
-keep pedal depressed with something
-tighten fittings at ports
-let pedal up so that fluid is replaced from the reservoir
-Check if pedal is firm, if not repeat.

Use rags to catch fluid and wash down area after.

--
1980 245 Canadian B21A with SU carb, M46 trans, 3:31 dif, in Brampton, Ont.

Hi,

My thoughts are that you need to push the rod to push the air and fluid through the spaces in the master cylinder.
The only difference is where you have it held in place.
Past that if you spill fluid on something, whether on a bench that's not painted, it's just a wipe up when you get around to it.
In the car you will want to jump on it right away. Not so good, if the fluid hits paint or rubber on the way down to the ground.
If you use a catch pan or a nice fluffy pillow, from someone else side of the bed, that could be detrimental to your health, if you know what I mean! (:-(

You really don't want to wait on an answer from a slow responding Brickboard. The brake fluid absorbs moisture, so you want to get the system closed up as soon as possible.

I answered from the way I do it on the car! That way you are not juggling a filled reservoir about.

You best believe, I have never spilt a drop of any brake fluid, in my life.
100% as Trump would say!
Besides, I bet, the First Lady travels keeping her own pillow with her now.
Just like my wife, (:-) she knows who she's sleeping with!

Phil