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What Pressure for Pressure Bleeding Brakes?

Posted: Mon Jul 07, 2025 4:39 am
by WarrenD
Finally got the new wheel cylinder installed (I hate that spring on top that pulls the shoes in!) and found an adapter that screws into the top of the master cylinder. I've installed a milton quick connect male fitting that my air hose plugs into so I can supply compressed air to the master. Just wondering what pressure to use (yes, I have moisture protection on the line close to the fitting.)
I seem to recall service pressure in hydraulic brake lines is well into the hundreds (if not thousands) of psi but I'm not wanting to use any more than needed to get the brakes bled.
Thanks!

Re: What Pressure for Pressure Bleeding Brakes?

Posted: Mon Jul 07, 2025 7:24 am
by just me
I never use pressurized air to bleed brakes. If DOT 5,
you can entrain air into the fluid and have difficulty getting a good pedal.
I use vacuum or the tried and true pump and bleed method. (2 man or 1 man with bleed bottle.)
You shouldn't need more than 3lbs or so if you are going to pressure bleed.

Re: What Pressure for Pressure Bleeding Brakes?

Posted: Mon Jul 07, 2025 7:48 am
by WarrenD
Thanks. I'm using DOT 3. If I had someone to help, I'd go that route which is what I did the last 2 times I've done this but there isn't anyone local with time to help.

Re: What Pressure for Pressure Bleeding Brakes?

Posted: Mon Jul 07, 2025 10:42 am
by just me
Then make a 1 man bleeder bottle. Easy peasy.

Re: What Pressure for Pressure Bleeding Brakes?

Posted: Mon Jul 07, 2025 1:43 pm
by WarrenD
Ok, I found a video showing how to make the bottle so maybe I'll give that a try first. I guess I'm skeptical that it won't suck air back in when I release the brake pedal.

Re: What Pressure for Pressure Bleeding Brakes?

Posted: Mon Jul 07, 2025 2:10 pm
by just me
If the tube is submerged, it can't. Thanks, physics.

Re: What Pressure for Pressure Bleeding Brakes?

Posted: Mon Jul 07, 2025 3:37 pm
by W_A_Watson_II
I use ~20 PSI.

Re: What Pressure for Pressure Bleeding Brakes?

Posted: Tue Jul 08, 2025 1:31 am
by WarrenD
Thanks!

Re: What Pressure for Pressure Bleeding Brakes?

Posted: Thu Jul 10, 2025 6:30 am
by Cal_Gary
My Motive Power Bleeder suggests 30PSI.
Gary

Re: What Pressure for Pressure Bleeding Brakes?

Posted: Thu Jul 10, 2025 6:34 am
by WarrenD
I used 15-20 psi and the flow was leisurely but got the job done.