Here's another question I hope someone can help with. I searched the site for info on bench bleeding a MC. The instructions appear contradictory.

Some people say to push the MC push rod all the way in until it bottoms (with a screwdriver or something else). Others say not to push it all the way in as that will damage the MC.

I'm confused and don't want to wreck the new master cylinder that I plan to buy. How far does one push in the push rod?

Thanks!!

If you're going to buy a new master cylinder,
refer to the written instructions that come with the new unit. You should also receive a "bleeder kit" with the new unit.

Didn't get instructions or bleeder kit with my new master cylinder, so it would be interesting if someone would let us know the do's and don'ts. I usually find out about the don'ts the hard way, so it would be good to know in advance this time. smile.gif

It should come with 2 plastic plugs ,bolt them into the line holes. Fill the master cylinder half way with brake fluid. Use a blunt tool, push in the piston no more than 3/4" of an inch. Do this slowly until all air bubbles disappear.When you are finished you probably won't be able to push in the tool anymore than an 1/8" of an inch.Don't bottom it out, as said you'll ruin the master cylinder.If all this fails, refer to your instructions

The instructions on my MC said to NOT bottom up the piston and go 3/4" (Raybold/Raybestos brand)

That might be the case if you're using the plugs, but what if you use brake lines (return lines to the bowls)?

OK, I just did this yesterday and the instructions that came with my cylinder stated
"Fill the reservoir with clean brake fluid. Check and make sure the bleeding tubes are fully submerged. Use a dowel or phillips screwdriver then slowly depress the plunger to the bottom of it's bore. Let the plunger return very slowly under it's own pressure. Fully depress and release the master cylinder plunger, in slow, even stokes, 10 to 20 times. "Top off" the brake fluid as needed to keep it full. Depress and release the plunger in a series of short strokes (about 1/4 of the full stroke length).
While doing this, tap the bottom of the master cylinder casting with a small wrench or bar to free any trapped air bubbles. Bleeding is done when plunger strokes no longer cause air bubbles in the clear tubes." Hope this helps. Dave

That sure helps! Thanks!

After having a piston stick in its bore, or a seal curl, you will never want to bottom out a master cylinder again. For one, it is not necessary, and for 2, it can damage it.
Been there.
For every instruction manual saying to bottom the bore while bleeding, there are 3 that say not to.

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