I am really embarrassed to ask such a basic question after owning my Mopar for over 50 years, but here it is: my 69 roadrunner has had a brake failure due to a bad master cylinder; now it has been rebuilt, but I need to bleed the whole system. The car has power brakes, and the question is: does the engine have to be on while bleeding each wheel or can I do it with the engine off? Thank you.

You can do it with engine off, I like to take the check valve off the master to make the pedal easier while doing it.
Some may not agree with me but that's how I do it after bench bleeding the master.
Ron

I have never bled power brakes with the engine running nor have I ever seen someone else bleed power brakes with the engine running. That's just me. Don't see why the engine would need to be running just to make vacuum for the power booster when all you are doing is pushing fluid mechanically through the system and not trying to stop a three or four thousand pound vehicle?

BTW I was always taught that no question is dumb and not, I'll also say, be embarrassing. I think this was a good question

As an aside, I used a Motive power bleeder. Oh does it make it so easy to bleed the brakes.

Nothing to be embarrassed about. That's a legitimate question.

I do not bleed with the engine running. The booster makes it hard to feel the brakes get hard or "pump up" when bleeding.

Bleed the master cylinder cylinder first. Some do it before they put it in the car but I use hoses connected to the ports that push the fluid back into the reservoir. Fill the reservoir above the hose ends and slowly press the pedal to the floor 2 or 3 times making sure the hose ends do not get air in them.

I then gravity bleed followed by pump bleeding the system.

Must be something in this Fall air, my master cylinder just failed on my 69 Road Runner a few weeks ago. Mine is a manual brake set up though.

Hope your failure wasn't as interesting as mine, I lost all brakes and took a little trip around the side on my garage, through some gravel, over my man door walkway, through my back yard and got it slowed down enough to slam it in park. Didn't hit or touch anything though. Could have been much worse.

Bench bled the new master last weekend, threw it on the car and bled the brakes, good to go now.

For those of you replacing masters, It's a good time to inspect / replace the wheel cylinders and calipers as well. Had one just this week that I assumed were fine due to us replacing them ~ 10 years back. For some reason after all was done and bled I decided to pull a rea drum and the W/C was just damp with fluid. Peeling back the dust seal revealed rust . So, I got to bleed the system again after replacing the W/C and calipers

i know several good DIY guys that open one bleeder screw at a time amd wait until they get a solid flow of brake fluid out of it and then do the next one,
I was taught when bleeding brakes with the older single piston master cylinders to start bleeding at the right rear and then do the left rear, then move up to the right front and then finish at the L.F. the one closest wheel cylinder to the master cylinder
I do the same way on the new dual piston M.C., bleed the farthest one first and then do the closet one to the MC, front or rear first doesn't matter to me

i would think that using one of those "one man" bleeders like a Mighty Vac would do everything you need.

My one-person method is to put a piece of vac hose over the bleeder screw, stick the other end of the hose in a partially filled jar of brake fluid so the end of the hose is submerged. Then open the bleeder and pump the brakes until there are no bubbles coming out into the jar.

The only trick to it is getting in a position where you can see the jar and pump the pedal at the same time.

I have never heard of anyone starting the car to bleed the brakes.

Before you go any further with the bleeding of the system, seeing that the master has been rebuilt/replaced, best to check the air gap between the booster's rod and the bore of the new master, even if it's the original unit rebuilt, dimensions can change, too large an air gap, the pedal will always be on the floor, too tight or no gap will result in the front calipers dragging....Mopars generally are good with .060 air gap.....and can we assume you have/plan to bench bleed the master before install?


Here's some pics to understand the "air gap"...

i ask "stoopid old guy questions" all the time.
nothing to be ashamed about asking ! [what was the topic again ? ]
all good things added to check as well.
remember : "Speed doesn't Kill. It's the SUDDEN STOP that does you in every time !"..................

My failure occurred while I was on an expressway to see my painter. I was doing around 60 mph and the red “brake” light in my dash came suddenly on and went off after about 30 seconds, so I did not worry much, but when I got to my exit I realized I had no brakes! Luckily it was Sunday morning and the car managed the exit and I made it to the shop, but that was a pucker moment I will not forget.

Let off the throttle all the way and downshift into 2nd gear and get ready to use the emergency brake when needed to complete the stop.
'I'm glad you and the car were not hurt or injured: up:
I went through a 6 ft. tall chain link fence at work when my old 1963 Plymouth M.W. car throttle stuck at WOT while goofing around driving it into our work yard one morning due to the left rear wheel cylinder failing when I jump on the brakes hard to try and stop it.
I'm glad that didn't tear the car up more than it did, it tore the 426 hood emblem off and scratched the front of the hood and roof above the windshield, not good.
That incident scared the keck out of me and made me think a lot more after that before doing stupid things in a car with some power work:

My brake failure story:

Out in our storage yard in Phoenix, AZ., I was tasked with airing-up the tires on a '65 GTO & moving the car. I started it & backed it out of the slot - it was obviously hard to roll because all 4 tires were flat, but it felt like it had brake pedal pressure. I aired the tires, started it & it was on a high idle, I put it in gear (automatic), & forward I went kind of quickly - I went for the brakes & nothing - NO BRAKES at all! I had about 50' to make a decision on what to do - either plow into a beautiful 1975 Roadrunner I had purchased at a used car lot (with 35,000 original miles I might add), or take the GTO out the gate & into a busy road - Broadway. I took the GTO into the Roadrunner to stop it & I let out a helluva yell as I hit it. I didn't even have time to think about hitting the emergency brake or jam it into park - it happened so fast. I tried to pump-up the brakes but the system had to be empty. I was SO pissed! I stove-in the RR quarter panel behind the wheel about 10", but the GTO came to a rest. I feel the sickening feeling every time I think about it!

Any idea where I could find one of those tools?

Never mind, I found them on ebay