Yes, that's normal. That is what allows "gravity-bleeding" without a helper. That is the only method I use.
I can share a trick when replacing the master cylinder. Loosen the two soft metal line nuts just a little. Unbolt the master cylinder from the booster, pull it forward off the mounting studs, then use it as a handle to bend the lines up just a little. That will prevent the fluid from running out of the lines. Remove the lines all the way. Watch out for brake fluid on the paint. Wash that off with water right away.
Bench-bleed the new part on the workbench, not on the vehicle. Often on GM trucks the master cylinder sits higher in the front. Air can get trapped in the high spot where it won't come out.
Run the lines into the new master cylinder and tighten the nuts hand tight. Use it to bend the lines back down, then bolt it to the power booster. Tighten one nut, then, with your helper, have him slowly push the brake pedal halfway to the floor. It should take about fifteen seconds to go halfway. Faster than that will push air down the lines and make bleeding more difficult. You'll see bubbles coming out by the loose nut. Tighten that nut, then holler to the helper to release the pedal. Loosen that nut and do that a second time, and a third time if necessary. Tighten that nut before the pedal is released, then do that for the second line. If a few tiny bubbles are left in the lines, they'll float back up while the brake pedal is held down, as in when sitting at a stop light, then when the brakes are released, the fluid rushing back will wash those bubbles into the reservoir.
I've used this procedure for over 40 years, except I skip the part of using a helper. The brake fluid will run out of the ports much slower if you keep the cap on tight on the reservoir.
The reason I specified running the brake pedal no more than halfway to the floor is with any master cylinder more than about a year old, crud and corrosion build up in the lower halves of the bores where the pistons don't normally travel. Pushing the pedal to the floor, as even some service manuals tell you to do, runs the rubber lip seals over that crud and can rip them. That results in a slowly sinking pedal that often doesn't show up until two or three days later. That's not a concern with a newly rebuilt master cylinder, but it's still a good practice to get into. Pretend there's a block of wood under the pedal.
This trick also does away with bleeding at the wheels as a lot of competent do-it-yourselfers mistakenly think you have to do. Pushing any air down the lines presents a new problem on most vehicles with anti-lock brakes. A few systems are self-bleeding, but in most, the air pools in some of the chambers resulting in a low, mushy brake pedal. The only way to get that air out is to use a scanner with the ABS bleeding capability. The procedure just takes a few seconds, but you have to have the scanner first.
One more trick to be aware of; if you have to open or remove a line and the brake fluid is running out of the port(s), place a stick between the front seat and the brake pedal to hold the pedal down about an inch. That moves the lip seals past the fluid return ports into the reservoir. Gravity won't be strong enough to pull the brake fluid past those seals.
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Saturday, July 16th, 2022 AT 7:56 PM
