Brakes hard after bleed, but loosen immediately after car startup

2000 HONDA CIVIC
193,000 MILES • 4 CYL • FWD • AUTOMATIC
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MATT COALE
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I have been trying to get to the bottom of a problem I've been having with my civic over the past few days. I replaced both rear drum brakes and wheel cylinders last week. Since I replaced the cylinders, I bled the brakes. I did this alone using this method: https://www.youtube.com/watch?v=n1NvtUwfRJc (Just bled the rear brakes).

Let me back up. After replacing the first brake (left rear), I took the car for a test drive and the brakes seemed just fine. They were nice and hard and felt how they should.

Then when I replaced the rear right, I did the same exact method (except for the wheel cylinder, because it had a rounded bolt), bleeding that cylinder after replacing the brake components . This time, I somehow got air in my system, and bled all four brakes until I had no bubbles in this sequence: rr, rl, fr, fl. They seemed to be nice and tight, so I was going to take the car on a test drive, and as soon as I started the car, the pedal had so much play, I could hit the floor with it, although the stopping and holding seemed to work fine--and still does.

After taking the right brake apart again and checking for possible errors (this was my first drum brake job), I went ahead and bled that wheel cylinder again because I replaced it this time, after hours of getting the dumb rounded bolt off. My brake pedal became tight again. I thought I had it, but I got the same result when I got ready for another test drive.

I'm wondering what the cause of this might be? Would you recommend going to each bleeder valve again and bleeding that way?

Additionally: The reason I decided to replace the drum brakes in the first place is because I kept hearing a tapping noise while pressing down on the brakes at lower speeds (30-5mph). It sounded like once per revolution. I took the car to work this morning and it is still making that noise. Not sure what to do about it, and help would be appreciated. I'm a little hard of hearing, but it sounds to me like it's coming from the back right side of the car.
Mar 20, 2017 at 1:14 PM
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CARADIODOC
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Did you reuse the old brake drums? If so, were they machined when you installed the new shoes? For the noise, the typical cause is the drum is out-of-round, and grooves have worn into the backing plate where the shoe frames rest on it.

Does the car have anti-lock brakes? Did the brake fluid reservoir run empty while you had the wheel cylinders off? How did you bleed the system? Did you let the fluid gravity-bleed, or did you use a helper to push the brake pedal?
Mar 16, 2021 at 11:44 AM
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MATT COALE
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The drums are actually brand new from Napa. I made sure to clean them with brake clean before installing. I figured I'd just replace everything I could to help eliminate that nasty tapping noise.

I am honestly unsure if my car has ABS. I cannot see an ABS light on the dash at all, but I am really unsure. I read that 96-00 Honda Civics didn't come with ABS by default. Mine is a 2000.

As far as bleeding, I did it by myself using this method: https://www.youtube.com/watch?v=1wwq1Vlk4Wg
Mar 16, 2021 at 11:44 AM
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CARADIODOC
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I watched the video, but my laptop will not play internet sound. You will never find a mechanic doing that. It is fine if you have plenty of time to spare, but wasting that much customers' time would get him fired. I have used a few vacuum bleeders on some tough cars, but air is going to get sucked in around the threads of the bleeder screw. You'll always see a steady stream of tiny bubbles that make it look like you're still getting air out of the system.

In this case, it is not a home-made vacuum bleeder. It's just a means of collecting the old fluid. We normally just let the brake fluid run down the back side of the backing plate, then wash it off with Brake Parts Cleaner when we're done. A few of us use a hose to run the fluid into the drain pan, but it's still a messy job.

What I would do next is bleed a little fluid from each wheel and verify you're getting new, clear fluid. If it's dark yet, meaning it was hot, (normal), there is likely still air in that line. If the fluid flows slowly at one wheel, it is possible for air bubbles to keep floating back up to a high spot and never come out. Pedal-bleeding with a helper will solve that, but it is is important to never ever push the pedal over half way to the floor. Crud and corrosion build up in the lower halves of the bores in the master cylinder where the pistons don't normally travel. Running the pedal all the way to the floor runs the rubber lip seals over that crud and can rip them. That typically causes a slowly-sinking pedal, and that might not show up for two or three days.

As a last resort, when you suspect air is in a line feeding a caliper, you can loosen the cap on the reservoir, then use a flat-blade screwdriver to pry the piston into the caliper housing. That will rapidly push a lot of fluid up into the reservoir, along with the air bubbles in it.
Mar 16, 2021 at 11:44 AM