[dhcarguy]

I am going to replace all my wheel cylinders and the 3 rubber brake lines.
How do I bleed the Master cylinder while still on the car.

Thanks, Dave

[camerjeff]

You should not have to, I would pinch off the old rubber rubber lines, make sure the master cylinder is kept topped off, replace the wheel cylinders, then the rubber lines one by one, making sure to frequently check the fluid level in the Master cylinder. As long as it does not run low there should not be an issue.

In fact when I purchased my 67 Firebird a few years ago, the rear brake cylinders were bad, the fluid level on the rear reservoir of the Master Cylinder was Empty! After I replaced the wheel cylinders and shoes, I filled and bled the rear brakes and they seem to work fine. I didn't bleed the master cylinder.

[78w72]

X2... if the master was already on the car & working, there is no need to bleed it as if it were new/dry.

As mentioned pinch the lines when changing out the wheel cylinders then replace the rubber lines as fast as possible or figure out how to plug the metal line while doing that, in order to keep the master full.

If it needs to be bled on the car you can do the same procedure as if on the bench... run lines from the outlets back into the master, i use some cut off metal lines from a junkyard car bent back into the master, then just pump the pedal a bunch of times until no bubbles come out... can take like 50 pumps when its completely dry/new.

[dhcarguy]

Thanks, I will run a line then back into the MC. It is the original type single MC. (1965 GTO)

I should have mentioned I am going to try and replace the 30 year old metal lines also. Doesn't look like a fun job.

Dave

[Keith Seymore]

This might be a good time to go to a dual port master cylinder.

K

[george kujanski]

X2 on putting in a dual master. Now is the time.

George

[4dblnkldude]

You will have way better brakes! If you don't change the master, I'd just rip everything off and replace it, obviously be careful where brake fluid will drip. When its replaced open the rear wheel cylinder and see if it'll gravity bleed. It may take an hour for the master to go down an inch. Go inside or do something keep looking at the time if it is going down. If not you gotta pump it through. I never had any good luck with any speed bleeder or pumps. I even hooked an HVAC vacuum pump on one time and it did not pull through. Fresh brake fluid is killer, I buy it by the gallon and change it every 2-3 years.

[spartazoo]

X3 on the dual port MC. I just did this on my 66. Took me custom bending a couple brake lines, but worth it.

[Skip Fix]

If changing the rubber lines I just slide the nut back on the hard line and shove a vacuum cap on it until I put the new hose on and the attach to wheel wheel cylinder. Same on the rear wheel cylinders hard lines that go into them. If the MC has a really good residual pressure valve in it you may have to do the 2 person "open, down pedal close, pedal up" method if it will not gravity bleed. Had to do that on the recent Vette project i was working on.