Rebuilt Master Cylinder/Booster question

[Corey Bowcutt]

I am having my master cylinder and booster rebuilt and should be getting it back very soon.  My question is about bleeding the master cylinder.  I have heard of bench bleeding them before installation.  Not sure what exactly this means or how to do it so any help would be appreciated.  Also, I bleed my brakes by drawing a vacuum at the 4 wheel cylinders essentially sucking the brake fluid from the master cylinder through the brake lines.  With this approach is bench bleeding still necessary?

Thank you,  Corey

[shelbydoug]

What you do to bench bleed, is connect a hose to each fluid output, returning it to the reservoir. Fill the reservoir. Pump the cylinder until the air bubble stop.

It's been a while since I bled the brakes. I did use a vacuum pump. I seem to recall still needing to bleed the master on the bench though.

If you don't bench bleed the master, you will not build enough pressure to suck the fluid through.

It does seem to vary from car to car. I'm not sure why. If everything is out then it isn't a big deal to bench bleed the master. Hold it in a vice. Push the plunger with a 1/4" ratchet extension.

[TA Coupe]

The instructions I've received with Master cylinders concerning bench bleeding is that they said don't bottom the Piston when you push it in. Not sure exactly why but something to keep in mind when you do it.

   Roy

[gt350shelb]

+1 dont bottom the master  if bench bleeding /  I have had mixed results with  vacuum bleeding brakes (your results may vary) / Im old school and want to  bleed them manually / do not pump pedal 10 time and open bleeder/.....(this breaks up air in system to smaller  bubbles make s it harder to get out )  I hold pedal down 1 maybe 2 pumps  and  open and close bleeders

[The Going Thing]

Be sure to get a centering tool. If you bleed it without it you likely won't be able to get the dash light out.

[Steve McDonald Formally known as Mcdonas]

+1 dont bottom the master  if bench bleeding /  I have had mixed results with  vacuum bleeding brakes (your results may vary) / Im old school and want to  bleed them manually / do not pump pedal 10 time and open bleeder/.....(this breaks up air in system to smaller  bubbles make s it harder to get out )  I hold pedal down 1 maybe 2 pumps  and  open and close bleeders

+1

[Bob Gaines]

Be sure to get a centering tool. If you bleed it without it you likely won't be able to get the dash light out.

To clarify the tool is a pin that screws in place of the brake warning switch located at the distribution block. The pin tool keeps the internal piston in place while bleeding the brakes otherwise the the warning light piston will go from one side to the other inside the block and maybe not return to center where it needs to be for the brake light to turn off. NPD sells them.

[Corey Bowcutt]

Thank you all.  I do have this tool and in fact put it in place last night to make sure I understand how it works. 

Corey