Brake bleeding question: Master cylinder bench vs on car

[mmklaxer]

I'm about to bleed the brakes using the Motive pressure bleeder. I have a little more research to do to make sure I don't damage any seals. I read I shouldn't go over 5 PSI to avoid disrupting the seals in the master cylinders. Otherwise the bleeding process is just like any other.
- Watch the reservoir to avoid going dry
- start farthest from the master and work back
- might take 2 trips around the 4 brakes to get a nice solid pedal

My question involves the master cylinder. Lots of folks talk about bench bleeding it, but the manual doesn't state that as a requirement. Is that just a time saver, or is it necessary to get ALL air out of the system? I've also read about bench bleeding on the car by using a scrap piece of brake line routed back into the reservoir. Is all of the necessary, or can I just pressure bleed the entire system at once? The manual is a bit vague regarding this piece.

Thanks all!

[KDubU]

I did mine installed into the car but I have read bench bleeding the master makes it an easier go. My bleeding took a while.

[edwardb]

Bench bleeding is a generic term for getting air out of the master cylinder(s) before bleeding the whole system. Can be physically done on the bench before installing into the car. But it's potentially messy and no one likes working with brake fluid any more than necessary than me. Doing it after the MC's are on the car is very common and what I've done on my builds. Exactly as you described. Remove the actual feed line, put a short piece of brake line from the feed port back to the reservoir and pump the pedal until you get a solid fluid flow. Is it necessary when power bleeding as you've described? I'm not sure to be honest because I've always done it that way and never had any issues. It's recommended and not that hard, so haven't tried without. I haven't used the Motive pressure bleeder. But use the same process with a pressure cap. Has always worked well for me. For a brand new build I typically go around the bleeders several times just to make sure all the air is out.

[GoDadGo]

I did not bench bleed my MC's prior to installation.

I put the system together and then gravity bled it.
I started with the passenger side rear first, then the driver side rear.
After that I did the front passenger side, then the front driver's side last.
I repeated that process when I did a pedal pressure style bleed and it was complete.
You'll know if you are successful by the firmness of the pedal and the position of the balance bar.

NOTE:..If you have air in the system the pedal won't be firm.
..._.......The balance bar may favor one side or the other, but should NOT collapse.
..._.......If you have air in the system the balance bar will likely collapse to the MC that has air in that side of the system.

Good Luck, Happy Brake Bleeding & Watch Your Pinkies!