How much *&%^#$^ fluid to bleed rear brakes???

[Stocker]

[Rant] Pardon my frustration.... after replacing the MC (and bench bleeding it), front hoses, & rear shoes, I started bleeding the system, starting with rears first. Though I wonder why that should matter since the front & rear are two independent systems.....

Anyway the parts house had no clear tubing (to run from the bleeders to a catch can), so I used black hose. Pumped (with the brake pedal) fluid to each rear wheel cylinder, then each front caliper. Maybe this also pumped air into the lines? Maybe I should have been more patient and let gravity do its thing. Careful not to let the MC go dry. This took close to a quart of fluid.

Didn't like the black hose b/c I couldn't watch for air bubbles leaving the bleeders, but I found some clear tubing at a hardware store. Good!

My wife then helped me bleed each corner. Never could get the air out of the rear lines, gave up and bled the fronts. Didn't take long and they were good. Went back to the rears (actually left rear) and so far have gone through more than three 12-ounce cans of fluid. Still getting air bubbles. Fluid is coming out clean and I'm about to start pouring it back into the MC rather than buying any more new fluid.

What the heck am I doing wrong? Should I just keep at it and the bubbles will eventually be gone? Right now it seems like they are somehow being introduced into the system. I'm stumped, I'm frustrated, and this just makes no sense to me. We've spent at least a couple hours and are still purging air. [/Rant]

[sjarrett71]

Wow, I changed my master cylinder a couple weeks ago and barely went through any fluid bleeding the brakes. Bled them until new clean fluid came out of the lines with no air bubbles. Peddle is nice and stiff. Can you write a detailed description of how you are bleeding them? Maybe that would help diagnose the problem.

[68gmsee]

Shouldn't take more than a couple of small cans if your system is clean. One large one if you flush it.

If you bled the front with no problems then you should be doing it the correct procedure - "tightening before releasing". More than likely you are sucking in air from somewhere. I'd go through each connection and make sure they're tight and if all looks good, take the master cylinder back and ask for another one. I had a new m.c. crap out on me shortly after I installed it.

There's two pistons and seals inside and the one for the rear may be sucking in air???

[Stocker]

Originally Posted by sjarrett71

Can you write a detailed description of how you are bleeding them? Maybe that would help diagnose the problem.

For starters, I first purged as much of the old fluid out as I possibly could, using light air pressure and cracking each bleeder. Forgot to mention that in my first post, sorry. I did this because there's a possibility some of it was 40 years old.... it came out rather nasty looking. I wanted all new fresh fluid in the system. edit: that explains the first quart -- the rest has been added trying to rid the system of air.

As for bleeding, wife pumps the brake pedal a couple times, then holds it down while I crack the bleeder momentarily (watching fluid & air bubbles through the clear tubing) then I close the bleeder. Wife then releases the brake pedal and pumps it again, repeating the cycle. Same as I have done before.

The only difference is I that am replacing all the fluid in the lines. I just can't seem to get the air purged from the rears.....

[AirSpeed]

You should start at the right rear. Did you open the bleader at the top and close the bleader while your wife held the pedal down after each stroke? I rebuilt my brake system last winter and it only took one quart, that's including what I ran through to flush any old fluid out.
Sometimes air can leak in through the threads even if you have a hose submerged in fluid. I've had that happen while bleading brakes by myself.
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[Stocker]

Originally Posted by 68gmsee

More than likely you are sucking in air from somewhere. I'd go through each connection and make sure they're tight and if all looks good, take the master cylinder back and ask for another one. I had a new m.c. crap out on me shortly after I installed it.

There's two pistons and seals inside and the one for the rear may be sucking in air???

I wondered about it sucking in air but I can't picture where (or how) that might happen. All connections are tight (no leaks) and since the fluid is pressurized (at least when the brake pedal is pressed), fluid should seep out....?

Is there some way air could be getting introduced into the MC? If it were entering from the mounting area where it attaches to the booster, I'm not sure how it could get into the front reservoir (rear brakes) without affecting the rear reservoir (front brakes).

[Stocker]

Originally Posted by AirSpeed

You should start at the right rear. Did you open the bleader at the top and close the bleader while your wife held the pedal down after each stroke? I rebuilt my brake system last winter and it only took one quart, that's including what I ran through to flush any old fluid out.
Sometimes air can leak in through the threads even if you have a hose submerged in fluid. I've had that happen while bleading brakes by myself.

Well, the brake line goes to a tee at the differential and then to each rear wheel cylinder -- in fact, the tee is mounted to the right of center, so the left rear line is longer by a few inches. I wouldn't think that should make any difference, though..... the fluid doesn't know if it's making a right turn or a left turn at the tee fitting.

Yes, my wife holds steady pressure on the pedal while I open, then close the bleeder.

[68gmsee]

My wife hates it when I holler for help with the brakes...

What I usually do is tell her to push the pedal and hold it down. At the same time she's depressing I release the bleed valve and when she lets me know the pedal is down all the way, I tighten the bleed valve. I then tell her to release.

The trick is to not let the pedal go back up before you tighten the bleed valve. Also don't let the master cylinder run out of fluid.

[Stocker]

Originally Posted by 68gmsee

The trick is to not let the pedal go back up before you tighten the bleed valve. Also don't let the master cylinder run out of fluid.

Yes sir, covered on both parts.

[GuyO]

I bet good money your problem is because the hoses are higher than the bleeders. If I am right, pull your hoses down so that the bleeders are at the highest point. Also, be sure your bleeders are on top (not kidding), The driivers side rear is the furthest away by line distance. Start there, then passenger side rear, then passenger side front and drivers side front. I went through the same thing, after many frustrating attempts and even a brake shop couldn't bleed my new front and rear disc conversion. My hoses were arched above my bleeders. The new MC couldn't pump enough fluid to push out the air. When I pulled my first hose down and pumped, the bleeder tube bubbled like a fish tank pump. It took approx 10 "pedal down, open bleeder, close bleeder, pedal up" cycles to get all the air out per brake! Good luck, hope this helps. G.

[midniteblues]

Ive had good luck with tapping on the lines while I had the rear jacked up way high but you gotta watch how high because of spilling the mc